--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/lang/invoke/MethodHandles.java Wed Mar 23 23:02:31 2011 -0700
@@ -0,0 +1,2357 @@
+/*
+ * Copyright (c) 2008, 2011, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.invoke;
+
+import java.lang.reflect.*;
+import sun.invoke.WrapperInstance;
+import sun.invoke.util.ValueConversions;
+import sun.invoke.util.VerifyAccess;
+import sun.invoke.util.Wrapper;
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Arrays;
+import sun.reflect.Reflection;
+import static java.lang.invoke.MethodHandleStatics.*;
+
+/**
+ * This class consists exclusively of static methods that operate on or return
+ * method handles. They fall into several categories:
+ * <ul>
+ * <li>Lookup methods which help create method handles for methods and fields.
+ * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
+ * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
+ * <li>Wrapper methods which can convert between method handles and interface types.
+ * </ul>
+ * <p>
+ * @author John Rose, JSR 292 EG
+ */
+public class MethodHandles {
+
+ private MethodHandles() { } // do not instantiate
+
+ private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
+ static { MethodHandleImpl.initStatics(); }
+ // See IMPL_LOOKUP below.
+
+ //// Method handle creation from ordinary methods.
+
+ /**
+ * Returns a {@link Lookup lookup object} on the caller,
+ * which has the capability to access any method handle that the caller has access to,
+ * including direct method handles to private fields and methods.
+ * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
+ * Do not store it in place where untrusted code can access it.
+ */
+ public static Lookup lookup() {
+ return new Lookup();
+ }
+
+ /**
+ * Returns a {@link Lookup lookup object} which is trusted minimally.
+ * It can only be used to create method handles to
+ * publicly accessible fields and methods.
+ * <p>
+ * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
+ * of this lookup object will be {@link java.lang.Object}.
+ * <p>
+ * The lookup class can be changed to any other class {@code C} using an expression of the form
+ * {@linkplain Lookup#in <code>publicLookup().in(C.class)</code>}.
+ * Since all classes have equal access to public names,
+ * such a change would confer no new access rights.
+ */
+ public static Lookup publicLookup() {
+ return Lookup.PUBLIC_LOOKUP;
+ }
+
+ /**
+ * A <em>lookup object</em> is a factory for creating method handles,
+ * when the creation requires access checking.
+ * Method handles do not perform
+ * access checks when they are called, but rather when they are created.
+ * Therefore, method handle access
+ * restrictions must be enforced when a method handle is created.
+ * The caller class against which those restrictions are enforced
+ * is known as the {@linkplain #lookupClass lookup class}.
+ * <p>
+ * A lookup class which needs to create method handles will call
+ * {@link MethodHandles#lookup MethodHandles.lookup} to create a factory for itself.
+ * When the {@code Lookup} factory object is created, the identity of the lookup class is
+ * determined, and securely stored in the {@code Lookup} object.
+ * The lookup class (or its delegates) may then use factory methods
+ * on the {@code Lookup} object to create method handles for access-checked members.
+ * This includes all methods, constructors, and fields which are allowed to the lookup class,
+ * even private ones.
+ * <p>
+ * The factory methods on a {@code Lookup} object correspond to all major
+ * use cases for methods, constructors, and fields.
+ * Here is a summary of the correspondence between these factory methods and
+ * the behavior the resulting method handles:
+ * <code>
+ * <table border=1 cellpadding=5 summary="lookup method behaviors">
+ * <tr><th>lookup expression</th><th>member</th><th>behavior</th></tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
+ * <td>FT f;</td><td>(T) this.f;</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
+ * <td>static<br>FT f;</td><td>(T) C.f;</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
+ * <td>FT f;</td><td>this.f = x;</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
+ * <td>static<br>FT f;</td><td>C.f = arg;</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
+ * <td>T m(A*);</td><td>(T) this.m(arg*);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
+ * <td>static<br>T m(A*);</td><td>(T) C.m(arg*);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
+ * <td>T m(A*);</td><td>(T) super.m(arg*);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
+ * <td>C(A*);</td><td>(T) new C(arg*);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
+ * <td>(static)?<br>FT f;</td><td>(FT) aField.get(thisOrNull);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
+ * <td>(static)?<br>FT f;</td><td>aField.set(thisOrNull, arg);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
+ * <td>(static)?<br>T m(A*);</td><td>(T) aMethod.invoke(thisOrNull, arg*);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
+ * <td>C(A*);</td><td>(C) aConstructor.newInstance(arg*);</td>
+ * </tr>
+ * <tr>
+ * <td>{@linkplain java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
+ * <td>(static)?<br>T m(A*);</td><td>(T) aMethod.invoke(thisOrNull, arg*);</td>
+ * </tr>
+ * </table>
+ * </code>
+ * Here, the type {@code C} is the class or interface being searched for a member,
+ * documented as a parameter named {@code refc} in the lookup methods.
+ * The method or constructor type {@code MT} is composed from the return type {@code T}
+ * and the sequence of argument types {@code A*}.
+ * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
+ * The formal parameter {@code this} stands for the self-reference of type {@code C};
+ * if it is present, it is always the leading argument to the method handle invocation.
+ * The name {@code arg} stands for all the other method handle arguments.
+ * In the code examples for the Core Reflection API, the name {@code thisOrNull}
+ * stands for a null reference if the accessed method or field is static,
+ * and {@code this} otherwise.
+ * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
+ * for reflective objects corresponding to the given members.
+ * <p>
+ * The equivalence between looked-up method handles and underlying
+ * class members can break down in a few ways:
+ * <ul>
+ * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
+ * the lookup can still succeed, even when there is no equivalent
+ * Java expression or bytecoded constant.
+ * <li>Likewise, if {@code T} or {@code MT}
+ * is not symbolically accessible from the lookup class's loader,
+ * the lookup can still succeed.
+ * For example, lookups for {@code MethodHandle.invokeExact} and
+ * {@code MethodHandle.invokeGeneric} will always succeed, regardless of requested type.
+ * <li>If there is a security manager installed, it can forbid the lookup
+ * on various grounds (<a href="#secmgr">see below</a>).
+ * By contrast, the {@code ldc} instruction is not subject to
+ * security manager checks.
+ * </ul>
+ *
+ * <h3><a name="access"></a>Access checking</h3>
+ * Access checks are applied in the factory methods of {@code Lookup},
+ * when a method handle is created.
+ * This is a key difference from the Core Reflection API, since
+ * {@link java.lang.reflect.Method#invoke Method.invoke}
+ * performs access checking against every caller, on every call.
+ * <p>
+ * All access checks start from a {@code Lookup} object, which
+ * compares its recorded lookup class against all requests to
+ * create method handles.
+ * A single {@code Lookup} object can be used to create any number
+ * of access-checked method handles, all checked against a single
+ * lookup class.
+ * <p>
+ * A {@code Lookup} object can be shared with other trusted code,
+ * such as a metaobject protocol.
+ * A shared {@code Lookup} object delegates the capability
+ * to create method handles on private members of the lookup class.
+ * Even if privileged code uses the {@code Lookup} object,
+ * the access checking is confined to the privileges of the
+ * original lookup class.
+ * <p>
+ * A lookup can fail, because
+ * the containing class is not accessible to the lookup class, or
+ * because the desired class member is missing, or because the
+ * desired class member is not accessible to the lookup class.
+ * In any of these cases, a {@code ReflectiveOperationException} will be
+ * thrown from the attempted lookup. The exact class will be one of
+ * the following:
+ * <ul>
+ * <li>NoSuchMethodException — if a method is requested but does not exist
+ * <li>NoSuchFieldException — if a field is requested but does not exist
+ * <li>IllegalAccessException — if the member exists but an access check fails
+ * </ul>
+ * <p>
+ * In general, the conditions under which a method handle may be
+ * looked up for a method {@code M} are exactly equivalent to the conditions
+ * under which the lookup class could have compiled and resolved a call to {@code M}.
+ * And the effect of invoking the method handle resulting from the lookup
+ * is exactly equivalent to executing the compiled and resolved call to {@code M}.
+ * The same point is true of fields and constructors.
+ * <p>
+ * In some cases, access between nested classes is obtained by the Java compiler by creating
+ * an wrapper method to access a private method of another class
+ * in the same top-level declaration.
+ * For example, a nested class {@code C.D}
+ * can access private members within other related classes such as
+ * {@code C}, {@code C.D.E}, or {@code C.B},
+ * but the Java compiler may need to generate wrapper methods in
+ * those related classes. In such cases, a {@code Lookup} object on
+ * {@code C.E} would be unable to those private members.
+ * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
+ * which can transform a lookup on {@code C.E} into one on any of those other
+ * classes, without special elevation of privilege.
+ * <p>
+ * Although bytecode instructions can only refer to classes in
+ * a related class loader, this API can search for methods in any
+ * class, as long as a reference to its {@code Class} object is
+ * available. Such cross-loader references are also possible with the
+ * Core Reflection API, and are impossible to bytecode instructions
+ * such as {@code invokestatic} or {@code getfield}.
+ * There is a {@linkplain java.lang.SecurityManager security manager API}
+ * to allow applications to check such cross-loader references.
+ * These checks apply to both the {@code MethodHandles.Lookup} API
+ * and the Core Reflection API
+ * (as found on {@link java.lang.Class Class}).
+ * <p>
+ * Access checks only apply to named and reflected methods,
+ * constructors, and fields.
+ * Other method handle creation methods, such as
+ * {@link #convertArguments MethodHandles.convertArguments},
+ * do not require any access checks, and are done
+ * with static methods of {@link MethodHandles},
+ * independently of any {@code Lookup} object.
+ *
+ * <h3>Security manager interactions</h3>
+ * <a name="secmgr"></a>
+ * If a security manager is present, member lookups are subject to
+ * additional checks.
+ * From one to four calls are made to the security manager.
+ * Any of these calls can refuse access by throwing a
+ * {@link java.lang.SecurityException SecurityException}.
+ * Define {@code smgr} as the security manager,
+ * {@code refc} as the containing class in which the member
+ * is being sought, and {@code defc} as the class in which the
+ * member is actually defined.
+ * The calls are made according to the following rules:
+ * <ul>
+ * <li>In all cases, {@link SecurityManager#checkMemberAccess
+ * smgr.checkMemberAccess(refc, Member.PUBLIC)} is called.
+ * <li>If the class loader of the lookup class is not
+ * the same as or an ancestor of the class loader of {@code refc},
+ * then {@link SecurityManager#checkPackageAccess
+ * smgr.checkPackageAccess(refcPkg)} is called,
+ * where {@code refcPkg} is the package of {@code refc}.
+ * <li>If the retrieved member is not public,
+ * {@link SecurityManager#checkMemberAccess
+ * smgr.checkMemberAccess(defc, Member.DECLARED)} is called.
+ * (Note that {@code defc} might be the same as {@code refc}.)
+ * <li>If the retrieved member is not public,
+ * and if {@code defc} and {@code refc} are in different class loaders,
+ * and if the class loader of the lookup class is not
+ * the same as or an ancestor of the class loader of {@code defc},
+ * then {@link SecurityManager#checkPackageAccess
+ * smgr.checkPackageAccess(defcPkg)} is called,
+ * where {@code defcPkg} is the package of {@code defc}.
+ * </ul>
+ * In all cases, the requesting class presented to the security
+ * manager will be the lookup class from the current {@code Lookup} object.
+ */
+ public static final
+ class Lookup {
+ /** The class on behalf of whom the lookup is being performed. */
+ private final Class<?> lookupClass;
+
+ /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
+ private final int allowedModes;
+
+ /** A single-bit mask representing {@code public} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x01}, happens to be the same as the value of the
+ * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
+ */
+ public static final int PUBLIC = Modifier.PUBLIC;
+
+ /** A single-bit mask representing {@code private} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x02}, happens to be the same as the value of the
+ * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
+ */
+ public static final int PRIVATE = Modifier.PRIVATE;
+
+ /** A single-bit mask representing {@code protected} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x04}, happens to be the same as the value of the
+ * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
+ */
+ public static final int PROTECTED = Modifier.PROTECTED;
+
+ /** A single-bit mask representing {@code package} access (default access),
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value is {@code 0x08}, which does not correspond meaningfully to
+ * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
+ */
+ public static final int PACKAGE = Modifier.STATIC;
+
+ private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
+ private static final int TRUSTED = -1;
+
+ private static int fixmods(int mods) {
+ mods &= (ALL_MODES - PACKAGE);
+ return (mods != 0) ? mods : PACKAGE;
+ }
+
+ /** Tells which class is performing the lookup. It is this class against
+ * which checks are performed for visibility and access permissions.
+ * <p>
+ * The class implies a maximum level of access permission,
+ * but the permissions may be additionally limited by the bitmask
+ * {@link #lookupModes lookupModes}, which controls whether non-public members
+ * can be accessed.
+ */
+ public Class<?> lookupClass() {
+ return lookupClass;
+ }
+
+ // This is just for calling out to MethodHandleImpl.
+ private Class<?> lookupClassOrNull() {
+ return (allowedModes == TRUSTED) ? null : lookupClass;
+ }
+
+ /** Tells which access-protection classes of members this lookup object can produce.
+ * The result is a bit-mask of the bits
+ * {@linkplain #PUBLIC PUBLIC (0x01)},
+ * {@linkplain #PRIVATE PRIVATE (0x02)},
+ * {@linkplain #PROTECTED PROTECTED (0x04)},
+ * and {@linkplain #PACKAGE PACKAGE (0x08)}.
+ * <p>
+ * A freshly-created lookup object
+ * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
+ * has all possible bits set, since the caller class can access all its own members.
+ * A lookup object on a new lookup class
+ * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
+ * may have some mode bits set to zero.
+ * The purpose of this is to restrict access via the new lookup object,
+ * so that it can access only names which can be reached by the original
+ * lookup object, and also by the new lookup class.
+ */
+ public int lookupModes() {
+ return allowedModes & ALL_MODES;
+ }
+
+ /** Embody the current class (the lookupClass) as a lookup class
+ * for method handle creation.
+ * Must be called by from a method in this package,
+ * which in turn is called by a method not in this package.
+ * <p>
+ * Also, don't make it private, lest javac interpose
+ * an access$N method.
+ */
+ Lookup() {
+ this(getCallerClassAtEntryPoint(), ALL_MODES);
+ // make sure we haven't accidentally picked up a privileged class:
+ checkUnprivilegedlookupClass(lookupClass);
+ }
+
+ Lookup(Class<?> lookupClass) {
+ this(lookupClass, ALL_MODES);
+ }
+
+ private Lookup(Class<?> lookupClass, int allowedModes) {
+ this.lookupClass = lookupClass;
+ this.allowedModes = allowedModes;
+ }
+
+ /**
+ * Creates a lookup on the specified new lookup class.
+ * The resulting object will report the specified
+ * class as its own {@link #lookupClass lookupClass}.
+ * <p>
+ * However, the resulting {@code Lookup} object is guaranteed
+ * to have no more access capabilities than the original.
+ * In particular, access capabilities can be lost as follows:<ul>
+ * <li>If the new lookup class differs from the old one,
+ * protected members will not be accessible by virtue of inheritance.
+ * (Protected members may continue to be accessible because of package sharing.)
+ * <li>If the new lookup class is in a different package
+ * than the old one, protected and default (package) members will not be accessible.
+ * <li>If the new lookup class is not within the same package member
+ * as the old one, private members will not be accessible.
+ * <li>If the new lookup class is not accessible to the old lookup class,
+ * then no members, not even public members, will be accessible.
+ * (In all other cases, public members will continue to be accessible.)
+ * </ul>
+ *
+ * @param requestedLookupClass the desired lookup class for the new lookup object
+ * @return a lookup object which reports the desired lookup class
+ * @throws NullPointerException if the argument is null
+ */
+ public Lookup in(Class<?> requestedLookupClass) {
+ requestedLookupClass.getClass(); // null check
+ if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
+ return new Lookup(requestedLookupClass, ALL_MODES);
+ if (requestedLookupClass == this.lookupClass)
+ return this; // keep same capabilities
+ int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
+ if ((newModes & PACKAGE) != 0
+ && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~(PACKAGE|PRIVATE);
+ }
+ // Allow nestmate lookups to be created without special privilege:
+ if ((newModes & PRIVATE) != 0
+ && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~PRIVATE;
+ }
+ if (newModes == PUBLIC
+ && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass)) {
+ // The requested class it not accessible from the lookup class.
+ // No permissions.
+ newModes = 0;
+ }
+ checkUnprivilegedlookupClass(requestedLookupClass);
+ return new Lookup(requestedLookupClass, newModes);
+ }
+
+ // Make sure outer class is initialized first.
+ static { IMPL_NAMES.getClass(); }
+
+ /** Version of lookup which is trusted minimally.
+ * It can only be used to create method handles to
+ * publicly accessible members.
+ */
+ static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
+
+ /** Package-private version of lookup which is trusted. */
+ static final Lookup IMPL_LOOKUP = new Lookup(Object.class, TRUSTED);
+
+ private static void checkUnprivilegedlookupClass(Class<?> lookupClass) {
+ String name = lookupClass.getName();
+ if (name.startsWith("java.lang.invoke."))
+ throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
+ }
+
+ /**
+ * Displays the name of the class from which lookups are to be made.
+ * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
+ * If there are restrictions on the access permitted to this lookup,
+ * this is indicated by adding a suffix to the class name, consisting
+ * of a slash and a keyword. The keyword represents the strongest
+ * allowed access, and is chosen as follows:
+ * <ul>
+ * <li>If no access is allowed, the suffix is "/noaccess".
+ * <li>If only public access is allowed, the suffix is "/public".
+ * <li>If only public and package access are allowed, the suffix is "/package".
+ * <li>If only public, package, and private access are allowed, the suffix is "/private".
+ * </ul>
+ * If none of the above cases apply, it is the case that full
+ * access (public, package, private, and protected) is allowed.
+ * In this case, no suffix is added.
+ * This is true only of an object obtained originally from
+ * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
+ * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
+ * always have restricted access, and will display a suffix.
+ * <p>
+ * (It may seem strange that protected access should be
+ * stronger than private access. Viewed independently from
+ * package access, protected access is the first to be lost,
+ * because it requires a direct subclass relationship between
+ * caller and callee.)
+ * @see #in
+ */
+ @Override
+ public String toString() {
+ String cname = lookupClass.getName();
+ switch (allowedModes) {
+ case 0: // no privileges
+ return cname + "/noaccess";
+ case PUBLIC:
+ return cname + "/public";
+ case PUBLIC|PACKAGE:
+ return cname + "/package";
+ case ALL_MODES & ~PROTECTED:
+ return cname + "/private";
+ case ALL_MODES:
+ return cname;
+ case TRUSTED:
+ return "/trusted"; // internal only; not exported
+ default: // Should not happen, but it's a bitfield...
+ cname = cname + "/" + Integer.toHexString(allowedModes);
+ assert(false) : cname;
+ return cname;
+ }
+ }
+
+ // call this from an entry point method in Lookup with extraFrames=0.
+ private static Class<?> getCallerClassAtEntryPoint() {
+ final int CALLER_DEPTH = 4;
+ // 0: Reflection.getCC, 1: getCallerClassAtEntryPoint,
+ // 2: Lookup.<init>, 3: MethodHandles.*, 4: caller
+ // Note: This should be the only use of getCallerClass in this file.
+ assert(Reflection.getCallerClass(CALLER_DEPTH-1) == MethodHandles.class);
+ return Reflection.getCallerClass(CALLER_DEPTH);
+ }
+
+ /**
+ * Produces a method handle for a static method.
+ * The type of the method handle will be that of the method.
+ * (Since static methods do not take receivers, there is no
+ * additional receiver argument inserted into the method handle type,
+ * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
+ * The method and all its argument types must be accessible to the lookup class.
+ * If the method's class has not yet been initialized, that is done
+ * immediately, before the method handle is returned.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param refc the class from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails, or if the method is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public
+ MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ MemberName method = resolveOrFail(refc, name, type, true);
+ checkMethod(refc, method, true);
+ return MethodHandleImpl.findMethod(method, false, lookupClassOrNull());
+ }
+
+ /**
+ * Produces a method handle for a virtual method.
+ * The type of the method handle will be that of the method,
+ * with the receiver type (usually {@code refc}) prepended.
+ * The method and all its argument types must be accessible to the lookup class.
+ * <p>
+ * When called, the handle will treat the first argument as a receiver
+ * and dispatch on the receiver's type to determine which method
+ * implementation to enter.
+ * (The dispatching action is identical with that performed by an
+ * {@code invokevirtual} or {@code invokeinterface} instruction.)
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * <p>
+ * Because of the general equivalence between {@code invokevirtual}
+ * instructions and method handles produced by {@code findVirtual},
+ * if the class is {@code MethodHandle} and the name string is
+ * {@code invokeExact} or {@code invokeGeneric}, the resulting
+ * method handle is equivalent to one produced by
+ * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
+ * {@link java.lang.invoke.MethodHandles#genericInvoker MethodHandles.genericInvoker}
+ * with the same {@code type} argument.
+ *
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails, or if the method is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ MemberName method = resolveOrFail(refc, name, type, false);
+ checkMethod(refc, method, false);
+ MethodHandle mh = MethodHandleImpl.findMethod(method, true, lookupClassOrNull());
+ return restrictProtectedReceiver(method, mh);
+ }
+
+ /**
+ * Produces a method handle which creates an object and initializes it, using
+ * the constructor of the specified type.
+ * The parameter types of the method handle will be those of the constructor,
+ * while the return type will be a reference to the constructor's class.
+ * The constructor and all its argument types must be accessible to the lookup class.
+ * If the constructor's class has not yet been initialized, that is done
+ * immediately, before the method handle is returned.
+ * <p>
+ * Note: The requested type must have a return type of {@code void}.
+ * This is consistent with the JVM's treatment of constructor type descriptors.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param refc the class or interface from which the method is accessed
+ * @param type the type of the method, with the receiver argument omitted, and a void return type
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the constructor does not exist
+ * @throws IllegalAccessException if access checking fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ String name = "<init>";
+ MemberName ctor = resolveOrFail(refc, name, type, false, false, lookupClassOrNull());
+ assert(ctor.isConstructor());
+ checkAccess(refc, ctor);
+ MethodHandle rawMH = MethodHandleImpl.findMethod(ctor, false, lookupClassOrNull());
+ MethodHandle allocMH = MethodHandleImpl.makeAllocator(rawMH);
+ return fixVarargs(allocMH, rawMH);
+ }
+
+ /** Return a version of MH which matches matchMH w.r.t. isVarargsCollector. */
+ private static MethodHandle fixVarargs(MethodHandle mh, MethodHandle matchMH) {
+ boolean va1 = mh.isVarargsCollector();
+ boolean va2 = matchMH.isVarargsCollector();
+ if (va1 == va2) {
+ return mh;
+ } else if (va2) {
+ MethodType type = mh.type();
+ int arity = type.parameterCount();
+ return mh.asVarargsCollector(type.parameterType(arity-1));
+ } else {
+ throw new InternalError("already varargs, but template is not: "+mh);
+ }
+ }
+
+ /**
+ * Produces an early-bound method handle for a virtual method,
+ * as if called from an {@code invokespecial}
+ * instruction from {@code caller}.
+ * The type of the method handle will be that of the method,
+ * with a suitably restricted receiver type (such as {@code caller}) prepended.
+ * The method and all its argument types must be accessible
+ * to the caller.
+ * <p>
+ * When called, the handle will treat the first argument as a receiver,
+ * but will not dispatch on the receiver's type.
+ * (This direct invocation action is identical with that performed by an
+ * {@code invokespecial} instruction.)
+ * <p>
+ * If the explicitly specified caller class is not identical with the
+ * lookup class, or if this lookup object does not have private access
+ * privileges, the access fails.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method (which must not be "<init>")
+ * @param type the type of the method, with the receiver argument omitted
+ * @param specialCaller the proposed calling class to perform the {@code invokespecial}
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
+ Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
+ checkSpecialCaller(specialCaller);
+ MemberName method = resolveOrFail(refc, name, type, false, false, specialCaller);
+ checkMethod(refc, method, false);
+ MethodHandle mh = MethodHandleImpl.findMethod(method, false, specialCaller);
+ return restrictReceiver(method, mh, specialCaller);
+ }
+
+ /**
+ * Produces a method handle giving read access to a non-static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle's single argument will be the instance containing
+ * the field.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return makeAccessor(refc, name, type, false, false);
+ }
+
+ /**
+ * Produces a method handle giving write access to a non-static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take two arguments, the instance containing
+ * the field, and the value to be stored.
+ * The second argument will be of the field's value type.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return makeAccessor(refc, name, type, false, true);
+ }
+
+ /**
+ * Produces a method handle giving read access to a static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle will take no arguments.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return makeAccessor(refc, name, type, true, false);
+ }
+
+ /**
+ * Produces a method handle giving write access to a static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return makeAccessor(refc, name, type, true, true);
+ }
+
+ /**
+ * Produces an early-bound method handle for a non-static method.
+ * The receiver must have a supertype {@code defc} in which a method
+ * of the given name and type is accessible to the lookup class.
+ * The method and all its argument types must be accessible to the lookup class.
+ * The type of the method handle will be that of the method,
+ * without any insertion of an additional receiver parameter.
+ * The given receiver will be bound into the method handle,
+ * so that every call to the method handle will invoke the
+ * requested method on the given receiver.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set
+ * <em>and</em> the trailing array argument is not the only argument.
+ * (If the trailing array argument is the only argument,
+ * the given receiver value will be bound to it.)
+ * <p>
+ * This is equivalent to the following code:
+ * <blockquote><pre>
+MethodHandle mh0 = {@link #findVirtual findVirtual}(defc, name, type);
+MethodHandle mh1 = mh0.{@link MethodHandle#bindTo bindTo}(receiver);
+MethodType mt1 = mh1.type();
+if (mh0.isVarargsCollector() && mt1.parameterCount() > 0) {
+ mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
+return mh1;
+ * </pre></blockquote>
+ * where {@code defc} is either {@code receiver.getClass()} or a super
+ * type of that class, in which the requested method is accessible
+ * to the lookup class.
+ * (Note that {@code bindTo} does not preserve variable arity.)
+ * @param receiver the object from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ Class<? extends Object> refc = receiver.getClass(); // may get NPE
+ MemberName method = resolveOrFail(refc, name, type, false);
+ checkMethod(refc, method, false);
+ MethodHandle dmh = MethodHandleImpl.findMethod(method, true, lookupClassOrNull());
+ MethodHandle bmh = MethodHandleImpl.bindReceiver(dmh, receiver);
+ if (bmh == null)
+ throw method.makeAccessException("no access", this);
+ if (dmh.type().parameterCount() == 0)
+ return dmh; // bound the trailing parameter; no varargs possible
+ return fixVarargs(bmh, dmh);
+ }
+
+ /**
+ * Makes a direct method handle to <i>m</i>, if the lookup class has permission.
+ * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
+ * If <i>m</i> is virtual, overriding is respected on every call.
+ * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
+ * The type of the method handle will be that of the method,
+ * with the receiver type prepended (but only if it is non-static).
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param m the reflected method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflect(Method m) throws IllegalAccessException {
+ MemberName method = new MemberName(m);
+ assert(method.isMethod());
+ if (!m.isAccessible()) checkMethod(method.getDeclaringClass(), method, method.isStatic());
+ MethodHandle mh = MethodHandleImpl.findMethod(method, true, lookupClassOrNull());
+ if (!m.isAccessible()) mh = restrictProtectedReceiver(method, mh);
+ return mh;
+ }
+
+ /**
+ * Produces a method handle for a reflected method.
+ * It will bypass checks for overriding methods on the receiver,
+ * as if by a {@code invokespecial} instruction from within the {@code specialCaller}.
+ * The type of the method handle will be that of the method,
+ * with the special caller type prepended (and <em>not</em> the receiver of the method).
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class,
+ * as if {@code invokespecial} instruction were being linked.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param m the reflected method
+ * @param specialCaller the class nominally calling the method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
+ checkSpecialCaller(specialCaller);
+ MemberName method = new MemberName(m);
+ assert(method.isMethod());
+ // ignore m.isAccessible: this is a new kind of access
+ checkMethod(m.getDeclaringClass(), method, false);
+ MethodHandle mh = MethodHandleImpl.findMethod(method, false, lookupClassOrNull());
+ return restrictReceiver(method, mh, specialCaller);
+ }
+
+ /**
+ * Produces a method handle for a reflected constructor.
+ * The type of the method handle will be that of the constructor,
+ * with the return type changed to the declaring class.
+ * The method handle will perform a {@code newInstance} operation,
+ * creating a new instance of the constructor's class on the
+ * arguments passed to the method handle.
+ * <p>
+ * If the constructor's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param c the reflected constructor
+ * @return a method handle which can invoke the reflected constructor
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectConstructor(Constructor c) throws IllegalAccessException {
+ MemberName ctor = new MemberName(c);
+ assert(ctor.isConstructor());
+ if (!c.isAccessible()) checkAccess(c.getDeclaringClass(), ctor);
+ MethodHandle rawCtor = MethodHandleImpl.findMethod(ctor, false, lookupClassOrNull());
+ MethodHandle allocator = MethodHandleImpl.makeAllocator(rawCtor);
+ return fixVarargs(allocator, rawCtor);
+ }
+
+ /**
+ * Produces a method handle giving read access to a reflected field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * If the field is static, the method handle will take no arguments.
+ * Otherwise, its single argument will be the instance containing
+ * the field.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * @param f the reflected field
+ * @return a method handle which can load values from the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
+ return makeAccessor(f.getDeclaringClass(), new MemberName(f), f.isAccessible(), false);
+ }
+
+ /**
+ * Produces a method handle giving write access to a reflected field.
+ * The type of the method handle will have a void return type.
+ * If the field is static, the method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Otherwise, the two arguments will be the instance containing
+ * the field, and the value to be stored.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * @param f the reflected field
+ * @return a method handle which can store values into the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
+ return makeAccessor(f.getDeclaringClass(), new MemberName(f), f.isAccessible(), true);
+ }
+
+ /// Helper methods, all package-private.
+
+ MemberName resolveOrFail(Class<?> refc, String name, Class<?> type, boolean isStatic) throws NoSuchFieldException, IllegalAccessException {
+ checkSymbolicClass(refc); // do this before attempting to resolve
+ name.getClass(); type.getClass(); // NPE
+ int mods = (isStatic ? Modifier.STATIC : 0);
+ return IMPL_NAMES.resolveOrFail(new MemberName(refc, name, type, mods), true, lookupClassOrNull(),
+ NoSuchFieldException.class);
+ }
+
+ MemberName resolveOrFail(Class<?> refc, String name, MethodType type, boolean isStatic) throws NoSuchMethodException, IllegalAccessException {
+ checkSymbolicClass(refc); // do this before attempting to resolve
+ name.getClass(); type.getClass(); // NPE
+ int mods = (isStatic ? Modifier.STATIC : 0);
+ return IMPL_NAMES.resolveOrFail(new MemberName(refc, name, type, mods), true, lookupClassOrNull(),
+ NoSuchMethodException.class);
+ }
+
+ MemberName resolveOrFail(Class<?> refc, String name, MethodType type, boolean isStatic,
+ boolean searchSupers, Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
+ checkSymbolicClass(refc); // do this before attempting to resolve
+ name.getClass(); type.getClass(); // NPE
+ int mods = (isStatic ? Modifier.STATIC : 0);
+ return IMPL_NAMES.resolveOrFail(new MemberName(refc, name, type, mods), searchSupers, specialCaller,
+ NoSuchMethodException.class);
+ }
+
+ void checkSymbolicClass(Class<?> refc) throws IllegalAccessException {
+ Class<?> caller = lookupClassOrNull();
+ if (caller != null && !VerifyAccess.isClassAccessible(refc, caller))
+ throw new MemberName(refc).makeAccessException("symbolic reference class is not public", this);
+ }
+
+ void checkMethod(Class<?> refc, MemberName m, boolean wantStatic) throws IllegalAccessException {
+ String message;
+ if (m.isConstructor())
+ message = "expected a method, not a constructor";
+ else if (!m.isMethod())
+ message = "expected a method";
+ else if (wantStatic != m.isStatic())
+ message = wantStatic ? "expected a static method" : "expected a non-static method";
+ else
+ { checkAccess(refc, m); return; }
+ throw m.makeAccessException(message, this);
+ }
+
+ void checkAccess(Class<?> refc, MemberName m) throws IllegalAccessException {
+ int allowedModes = this.allowedModes;
+ if (allowedModes == TRUSTED) return;
+ int mods = m.getModifiers();
+ if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
+ return; // common case
+ int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
+ if ((requestedModes & allowedModes) != 0
+ && VerifyAccess.isMemberAccessible(refc, m.getDeclaringClass(),
+ mods, lookupClass()))
+ return;
+ if (((requestedModes & ~allowedModes) & PROTECTED) != 0
+ && VerifyAccess.isSamePackage(m.getDeclaringClass(), lookupClass()))
+ // Protected members can also be checked as if they were package-private.
+ return;
+ throw m.makeAccessException(accessFailedMessage(refc, m), this);
+ }
+
+ String accessFailedMessage(Class<?> refc, MemberName m) {
+ Class<?> defc = m.getDeclaringClass();
+ int mods = m.getModifiers();
+ // check the class first:
+ boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
+ (defc == refc ||
+ Modifier.isPublic(refc.getModifiers())));
+ if (!classOK && (allowedModes & PACKAGE) != 0) {
+ classOK = (VerifyAccess.isClassAccessible(defc, lookupClass()) &&
+ (defc == refc ||
+ VerifyAccess.isClassAccessible(refc, lookupClass())));
+ }
+ if (!classOK)
+ return "class is not public";
+ if (Modifier.isPublic(mods))
+ return "access to public member failed"; // (how?)
+ if (Modifier.isPrivate(mods))
+ return "member is private";
+ if (Modifier.isProtected(mods))
+ return "member is protected";
+ return "member is private to package";
+ }
+
+ private static final boolean ALLOW_NESTMATE_ACCESS = false;
+
+ void checkSpecialCaller(Class<?> specialCaller) throws IllegalAccessException {
+ if (allowedModes == TRUSTED) return;
+ if ((allowedModes & PRIVATE) == 0
+ || (specialCaller != lookupClass()
+ && !(ALLOW_NESTMATE_ACCESS &&
+ VerifyAccess.isSamePackageMember(specialCaller, lookupClass()))))
+ throw new MemberName(specialCaller).
+ makeAccessException("no private access for invokespecial", this);
+ }
+
+ MethodHandle restrictProtectedReceiver(MemberName method, MethodHandle mh) throws IllegalAccessException {
+ // The accessing class only has the right to use a protected member
+ // on itself or a subclass. Enforce that restriction, from JVMS 5.4.4, etc.
+ if (!method.isProtected() || method.isStatic()
+ || allowedModes == TRUSTED
+ || method.getDeclaringClass() == lookupClass()
+ || (ALLOW_NESTMATE_ACCESS &&
+ VerifyAccess.isSamePackageMember(method.getDeclaringClass(), lookupClass())))
+ return mh;
+ else
+ return restrictReceiver(method, mh, lookupClass());
+ }
+ MethodHandle restrictReceiver(MemberName method, MethodHandle mh, Class<?> caller) throws IllegalAccessException {
+ assert(!method.isStatic());
+ Class<?> defc = method.getDeclaringClass(); // receiver type of mh is too wide
+ if (defc.isInterface() || !defc.isAssignableFrom(caller)) {
+ throw method.makeAccessException("caller class must be a subclass below the method", caller);
+ }
+ MethodType rawType = mh.type();
+ if (rawType.parameterType(0) == caller) return mh;
+ MethodType narrowType = rawType.changeParameterType(0, caller);
+ MethodHandle narrowMH = MethodHandleImpl.convertArguments(mh, narrowType, rawType, null);
+ return fixVarargs(narrowMH, mh);
+ }
+
+ MethodHandle makeAccessor(Class<?> refc, String name, Class<?> type,
+ boolean isStatic, boolean isSetter) throws NoSuchFieldException, IllegalAccessException {
+ MemberName field = resolveOrFail(refc, name, type, isStatic);
+ if (isStatic != field.isStatic())
+ throw field.makeAccessException(isStatic
+ ? "expected a static field"
+ : "expected a non-static field", this);
+ return makeAccessor(refc, field, false, isSetter);
+ }
+
+ MethodHandle makeAccessor(Class<?> refc, MemberName field,
+ boolean trusted, boolean isSetter) throws IllegalAccessException {
+ assert(field.isField());
+ if (trusted)
+ return MethodHandleImpl.accessField(field, isSetter, lookupClassOrNull());
+ checkAccess(refc, field);
+ MethodHandle mh = MethodHandleImpl.accessField(field, isSetter, lookupClassOrNull());
+ return restrictProtectedReceiver(field, mh);
+ }
+ }
+
+ /**
+ * Produces a method handle giving read access to elements of an array.
+ * The type of the method handle will have a return type of the array's
+ * element type. Its first argument will be the array type,
+ * and the second will be {@code int}.
+ * @param arrayClass an array type
+ * @return a method handle which can load values from the given array type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if arrayClass is not an array type
+ */
+ public static
+ MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
+ return MethodHandleImpl.accessArrayElement(arrayClass, false);
+ }
+
+ /**
+ * Produces a method handle giving write access to elements of an array.
+ * The type of the method handle will have a void return type.
+ * Its last argument will be the array's element type.
+ * The first and second arguments will be the array type and int.
+ * @return a method handle which can store values into the array type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if arrayClass is not an array type
+ */
+ public static
+ MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
+ return MethodHandleImpl.accessArrayElement(arrayClass, true);
+ }
+
+ /// method handle invocation (reflective style)
+
+ /**
+ * Produces a method handle which will invoke any method handle of the
+ * given {@code type} on a standard set of {@code Object} type arguments
+ * and a single trailing {@code Object[]} array.
+ * The resulting invoker will be a method handle with the following
+ * arguments:
+ * <ul>
+ * <li>a single {@code MethodHandle} target
+ * <li>zero or more {@code Object} values (counted by {@code objectArgCount})
+ * <li>an {@code Object[]} array containing more arguments
+ * </ul>
+ * <p>
+ * The invoker will behave like a call to {@link MethodHandle#invokeGeneric invokeGeneric} with
+ * the indicated {@code type}.
+ * That is, if the target is exactly of the given {@code type}, it will behave
+ * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
+ * is used to convert the target to the required {@code type}.
+ * <p>
+ * The type of the returned invoker will not be the given {@code type}, but rather
+ * will have all parameter and return types replaced by {@code Object}, except for
+ * the last parameter type, which will be the array type {@code Object[]}.
+ * <p>
+ * Before invoking its target, the invoker will spread the varargs array, apply
+ * reference casts as necessary, and unbox and widen primitive arguments.
+ * The return value of the invoker will be an {@code Object} reference,
+ * boxing a primitive value if the original type returns a primitive,
+ * and always null if the original type returns void.
+ * <p>
+ * This method is equivalent to the following code (though it may be more efficient):
+ * <p><blockquote><pre>
+MethodHandle invoker = MethodHandles.genericInvoker(type);
+int spreadArgCount = type.parameterCount - objectArgCount;
+invoker = invoker.asSpreader(Object[].class, spreadArgCount);
+return invoker;
+ * </pre></blockquote>
+ * <p>
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @param objectArgCount number of fixed (non-varargs) {@code Object} arguments
+ * @return a method handle suitable for invoking any method handle of the given type
+ */
+ static public
+ MethodHandle spreadInvoker(MethodType type, int objectArgCount) {
+ if (objectArgCount < 0 || objectArgCount > type.parameterCount())
+ throw new IllegalArgumentException("bad argument count "+objectArgCount);
+ return type.invokers().spreadInvoker(objectArgCount);
+ }
+
+ /**
+ * Produces a special <em>invoker method handle</em> which can be used to
+ * invoke any method handle of the given type, as if by {@code invokeExact}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ * <p>
+ * This method is equivalent to the following code (though it may be more efficient):
+ * <p><blockquote><pre>
+publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)
+ * </pre></blockquote>
+ *
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * Invoker method handles can be useful when working with variable method handles
+ * of unknown types.
+ * For example, to emulate an {@code invokeExact} call to a variable method
+ * handle {@code M}, extract its type {@code T},
+ * look up the invoker method {@code X} for {@code T},
+ * and call the invoker method, as {@code X.invokeGeneric(T, A...)}.
+ * (It would not work to call {@code X.invokeExact}, since the type {@code T}
+ * is unknown.)
+ * If spreading, collecting, or other argument transformations are required,
+ * they can be applied once to the invoker {@code X} and reused on many {@code M}
+ * method handle values, as long as they are compatible with the type of {@code X}.
+ * <p>
+ * <em>(Note: The invoker method is not available via the Core Reflection API.
+ * An attempt to call {@linkplain java.lang.reflect.Method#invoke Method.invoke}
+ * on the declared {@code invokeExact} or {@code invokeGeneric} method will raise an
+ * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
+ * <p>
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle of the given type
+ */
+ static public
+ MethodHandle exactInvoker(MethodType type) {
+ return type.invokers().exactInvoker();
+ }
+
+ /**
+ * Produces a special <em>invoker method handle</em> which can be used to
+ * invoke any method handle of the given type, as if by {@code invokeGeneric}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ * <p>
+ * Before invoking its target, the invoker will apply reference casts as
+ * necessary and unbox and widen primitive arguments, as if by {@link #convertArguments convertArguments}.
+ * The return value of the invoker will be an {@code Object} reference,
+ * boxing a primitive value if the original type returns a primitive,
+ * and always null if the original type returns void.
+ * <p>
+ * This method is equivalent to the following code (though it may be more efficient):
+ * <p><blockquote><pre>
+publicLookup().findVirtual(MethodHandle.class, "invokeGeneric", type)
+ * </pre></blockquote>
+ * <p>
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle convertible to the given type
+ */
+ static public
+ MethodHandle genericInvoker(MethodType type) {
+ return type.invokers().genericInvoker();
+ }
+
+ /**
+ * Perform value checking, exactly as if for an adapted method handle.
+ * It is assumed that the given value is either null, of type T0,
+ * or (if T0 is primitive) of the wrapper type corresponding to T0.
+ * The following checks and conversions are made:
+ * <ul>
+ * <li>If T0 and T1 are references, then a cast to T1 is applied.
+ * (The types do not need to be related in any particular way.)
+ * <li>If T0 and T1 are primitives, then a widening or narrowing
+ * conversion is applied, if one exists.
+ * <li>If T0 is a primitive and T1 a reference, and
+ * T0 has a wrapper type TW, a boxing conversion to TW is applied,
+ * possibly followed by a reference conversion.
+ * T1 must be TW or a supertype.
+ * <li>If T0 is a reference and T1 a primitive, and
+ * T1 has a wrapper type TW, an unboxing conversion is applied,
+ * possibly preceded by a reference conversion.
+ * T0 must be TW or a supertype.
+ * <li>If T1 is void, the return value is discarded
+ * <li>If T0 is void and T1 a reference, a null value is introduced.
+ * <li>If T0 is void and T1 a primitive, a zero value is introduced.
+ * </ul>
+ * If the value is discarded, null will be returned.
+ * @param valueType
+ * @param value
+ * @return the value, converted if necessary
+ * @throws java.lang.ClassCastException if a cast fails
+ */
+ static
+ <T0, T1> T1 checkValue(Class<T0> t0, Class<T1> t1, Object value)
+ throws ClassCastException
+ {
+ if (t0 == t1) {
+ // no conversion needed; just reassert the same type
+ if (t0.isPrimitive())
+ return Wrapper.asPrimitiveType(t1).cast(value);
+ else
+ return Wrapper.OBJECT.convert(value, t1);
+ }
+ boolean prim0 = t0.isPrimitive(), prim1 = t1.isPrimitive();
+ if (!prim0) {
+ // check contract with caller
+ Wrapper.OBJECT.convert(value, t0);
+ if (!prim1) {
+ return Wrapper.OBJECT.convert(value, t1);
+ }
+ // convert reference to primitive by unboxing
+ Wrapper w1 = Wrapper.forPrimitiveType(t1);
+ return w1.convert(value, t1);
+ }
+ // check contract with caller:
+ Wrapper.asWrapperType(t0).cast(value);
+ Wrapper w1 = Wrapper.forPrimitiveType(t1);
+ return w1.convert(value, t1);
+ }
+
+ static
+ Object checkValue(Class<?> T1, Object value)
+ throws ClassCastException
+ {
+ Class<?> T0;
+ if (value == null)
+ T0 = Object.class;
+ else
+ T0 = value.getClass();
+ return checkValue(T0, T1, value);
+ }
+
+ /// method handle modification (creation from other method handles)
+
+ /**
+ * Produces a method handle which adapts the type of the
+ * given method handle to a new type by pairwise argument conversion.
+ * The original type and new type must have the same number of arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ * <p>
+ * If the original type and new type are equal, returns target.
+ * <p>
+ * The following conversions are applied as needed both to
+ * arguments and return types. Let T0 and T1 be the differing
+ * new and old parameter types (or old and new return types)
+ * for corresponding values passed by the new and old method types.
+ * Given those types T0, T1, one of the following conversions is applied
+ * if possible:
+ * <ul>
+ * <li>If T0 and T1 are references, then a cast to T1 is applied.
+ * (The types do not need to be related in any particular way.)
+ * <li>If T0 and T1 are primitives, then a Java method invocation
+ * conversion (JLS 5.3) is applied, if one exists.
+ * <li>If T0 is a primitive and T1 a reference, a boxing
+ * conversion is applied if one exists, possibly followed by
+ * a reference conversion to a superclass.
+ * T1 must be a wrapper class or a supertype of one.
+ * <li>If T0 is a reference and T1 a primitive, an unboxing
+ * conversion will be applied at runtime, possibly followed
+ * by a Java method invocation conversion (JLS 5.3)
+ * on the primitive value. (These are the widening conversions.)
+ * T0 must be a wrapper class or a supertype of one.
+ * (In the case where T0 is Object, these are the conversions
+ * allowed by java.lang.reflect.Method.invoke.)
+ * <li>If the return type T1 is void, any returned value is discarded
+ * <li>If the return type T0 is void and T1 a reference, a null value is introduced.
+ * <li>If the return type T0 is void and T1 a primitive, a zero value is introduced.
+ * </ul>
+ * @param target the method handle to invoke after arguments are retyped
+ * @param newType the expected type of the new method handle
+ * @return a method handle which delegates to {@code target} after performing
+ * any necessary argument conversions, and arranges for any
+ * necessary return value conversions
+ * @throws NullPointerException if either argument is null
+ * @throws WrongMethodTypeException if the conversion cannot be made
+ * @see MethodHandle#asType
+ * @see MethodHandles#explicitCastArguments
+ */
+ public static
+ MethodHandle convertArguments(MethodHandle target, MethodType newType) {
+ MethodType oldType = target.type();
+ if (oldType.equals(newType))
+ return target;
+ MethodHandle res = null;
+ try {
+ res = MethodHandleImpl.convertArguments(target,
+ newType, oldType, null);
+ } catch (IllegalArgumentException ex) {
+ }
+ if (res == null)
+ throw new WrongMethodTypeException("cannot convert to "+newType+": "+target);
+ return res;
+ }
+
+ /**
+ * Produces a method handle which adapts the type of the
+ * given method handle to a new type by pairwise argument conversion.
+ * The original type and new type must have the same number of arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ * <p>
+ * If the original type and new type are equal, returns target.
+ * <p>
+ * The same conversions are allowed as for {@link #convertArguments convertArguments},
+ * and some additional conversions are also applied if those conversions fail.
+ * Given types T0, T1, one of the following conversions is applied
+ * in addition, if the conversions specified for {@code convertArguments}
+ * would be insufficient:
+ * <ul>
+ * <li>If T0 and T1 are references, and T1 is an interface type,
+ * then the value of type T0 is passed as a T1 without a cast.
+ * (This treatment of interfaces follows the usage of the bytecode verifier.)
+ * <li>If T0 and T1 are primitives and one is boolean,
+ * the boolean is treated as a one-bit unsigned integer.
+ * (This treatment follows the usage of the bytecode verifier.)
+ * A conversion from another primitive type behaves as if
+ * it first converts to byte, and then masks all but the low bit.
+ * <li>If a primitive value would be converted by {@code convertArguments}
+ * using Java method invocation conversion (JLS 5.3),
+ * Java casting conversion (JLS 5.5) may be used also.
+ * This allows primitives to be narrowed as well as widened.
+ * </ul>
+ * @param target the method handle to invoke after arguments are retyped
+ * @param newType the expected type of the new method handle
+ * @return a method handle which delegates to {@code target} after performing
+ * any necessary argument conversions, and arranges for any
+ * necessary return value conversions
+ * @throws NullPointerException if either argument is null
+ * @throws WrongMethodTypeException if the conversion cannot be made
+ * @see MethodHandle#asType
+ * @see MethodHandles#convertArguments
+ */
+ public static
+ MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
+ return convertArguments(target, newType); // FIXME!
+ }
+
+ /*
+ FIXME: Reconcile javadoc with 10/22/2010 EG notes on conversion:
+
+ Both converters arrange for their method handles to convert arguments
+ and return values. The conversion rules are the same for arguments
+ and return values, and depend only on source and target types, S and
+ T. The conversions allowed by castConvertArguments are a strict
+ superset of those performed by convertArguments.
+
+ In all cases, if S and T are references, a simple checkcast is done.
+ If neither S nor T is a primitive, no attempt is made to unbox and
+ box. A failed conversion throws ClassCastException.
+
+ If T is void, the value is dropped.
+
+ For compatibility with reflection, if S is void and T is a reference,
+ a null value is produced.
+
+ For compatibility with reflection, if S is a reference and T is a
+ primitive, S is first unboxed and then undergoes primitive conversion.
+ In the case of 'convertArguments', only assignment conversion is
+ performed (no narrowing primitive conversion).
+
+ If S is a primitive, S is boxed, and then the above rules are applied.
+ If S and T are both primitives, the boxing will be undetectable; only
+ the primitive conversions will be apparent to the user. The key point
+ is that if S is a primitive type, the implementation may box it and
+ treat is as Object, without loss of information, or it may use a "fast
+ path" which does not use boxing.
+
+ Notwithstanding the rules above, for compatibility with the verifier,
+ if T is an interface, it is treated as if it were Object. [KEEP THIS?]
+
+ Also, for compatibility with the verifier, a boolean may be undergo
+ widening or narrowing conversion to any other primitive type. [KEEP THIS?]
+ */
+
+ /**
+ * Produces a method handle which adapts the calling sequence of the
+ * given method handle to a new type, by reordering the arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ * <p>
+ * The given array controls the reordering.
+ * Call {@code #I} the number of incoming parameters (the value
+ * {@code newType.parameterCount()}, and call {@code #O} the number
+ * of outgoing parameters (the value {@code target.type().parameterCount()}).
+ * Then the length of the reordering array must be {@code #O},
+ * and each element must be a non-negative number less than {@code #I}.
+ * For every {@code N} less than {@code #O}, the {@code N}-th
+ * outgoing argument will be taken from the {@code I}-th incoming
+ * argument, where {@code I} is {@code reorder[N]}.
+ * <p>
+ * No argument or return value conversions are applied.
+ * The type of each incoming argument, as determined by {@code newType},
+ * must be identical to the type of the corresponding outgoing argument
+ * or arguments in the target method handle.
+ * The return type of {@code newType} must be identical to the return
+ * type of the original target.
+ * <p>
+ * The reordering array need not specify an actual permutation.
+ * An incoming argument will be duplicated if its index appears
+ * more than once in the array, and an incoming argument will be dropped
+ * if its index does not appear in the array.
+ * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
+ * incoming arguments which are not mentioned in the reordering array
+ * are may be any type, as determined only by {@code newType}.
+ * <blockquote><pre>
+MethodType intfn1 = MethodType.methodType(int.class, int.class);
+MethodType intfn2 = MethodType.methodType(int.class, int.class, int.class);
+MethodHandle sub = ... {int x, int y => x-y} ...;
+assert(sub.type().equals(intfn2));
+MethodHandle sub1 = MethodHandles.permuteArguments(sub, intfn2, 0, 1);
+MethodHandle rsub = MethodHandles.permuteArguments(sub, intfn2, 1, 0);
+assert((int)rsub.invokeExact(1, 100) == 99);
+MethodHandle add = ... {int x, int y => x+y} ...;
+assert(add.type().equals(intfn2));
+MethodHandle twice = MethodHandles.permuteArguments(add, intfn1, 0, 0);
+assert(twice.type().equals(intfn1));
+assert((int)twice.invokeExact(21) == 42);
+ * </pre></blockquote>
+ * @param target the method handle to invoke after arguments are reordered
+ * @param newType the expected type of the new method handle
+ * @param reorder a string which controls the reordering
+ * @return a method handle which delegates to {@code target} after it
+ * drops unused arguments and moves and/or duplicates the other arguments
+ * @throws NullPointerException if any argument is null
+ */
+ public static
+ MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
+ MethodType oldType = target.type();
+ checkReorder(reorder, newType, oldType);
+ return MethodHandleImpl.convertArguments(target,
+ newType, oldType,
+ reorder);
+ }
+
+ private static void checkReorder(int[] reorder, MethodType newType, MethodType oldType) {
+ if (reorder.length == oldType.parameterCount()) {
+ int limit = newType.parameterCount();
+ boolean bad = false;
+ for (int i : reorder) {
+ if (i < 0 || i >= limit) {
+ bad = true; break;
+ }
+ }
+ if (!bad) return;
+ }
+ throw newIllegalArgumentException("bad reorder array");
+ }
+
+ /**
+ * Equivalent to the following code:
+ * <p><blockquote><pre>
+ * int spreadPos = newType.parameterCount() - 1;
+ * Class<?> spreadType = newType.parameterType(spreadPos);
+ * int spreadCount = target.type().parameterCount() - spreadPos;
+ * MethodHandle adapter = target.asSpreader(spreadType, spreadCount);
+ * adapter = adapter.asType(newType);
+ * return adapter;
+ * </pre></blockquote>
+ * @param target the method handle to invoke after argument spreading
+ * @param newType the expected type of the new method handle
+ * @return a method handle which spreads its final argument,
+ * before calling the original method handle
+ */
+ /*non-public*/ static
+ MethodHandle spreadArguments(MethodHandle target, MethodType newType) {
+ MethodType oldType = target.type();
+ int inargs = newType.parameterCount();
+ int outargs = oldType.parameterCount();
+ int spreadPos = inargs - 1;
+ int numSpread = (outargs - spreadPos);
+ MethodHandle res = null;
+ if (spreadPos >= 0 && numSpread >= 0) {
+ res = MethodHandleImpl.spreadArguments(target, newType, spreadPos);
+ }
+ if (res == null) {
+ throw newIllegalArgumentException("cannot spread "+newType+" to " +oldType);
+ }
+ return res;
+ }
+
+ /**
+ * Equivalent to the following code:
+ * <p><blockquote><pre>
+ * int collectPos = target.type().parameterCount() - 1;
+ * Class<?> collectType = target.type().parameterType(collectPos);
+ * if (!collectType.isArray()) collectType = Object[].class;
+ * int collectCount = newType.parameterCount() - collectPos;
+ * MethodHandle adapter = target.asCollector(collectType, collectCount);
+ * adapter = adapter.asType(newType);
+ * return adapter;
+ * </pre></blockquote>
+ * @param target the method handle to invoke after argument collection
+ * @param newType the expected type of the new method handle
+ * @return a method handle which collects some trailing argument
+ * into an array, before calling the original method handle
+ */
+ /*non-public*/ static
+ MethodHandle collectArguments(MethodHandle target, MethodType newType) {
+ MethodType oldType = target.type();
+ int inargs = newType.parameterCount();
+ int outargs = oldType.parameterCount();
+ int collectPos = outargs - 1;
+ int numCollect = (inargs - collectPos);
+ if (collectPos < 0 || numCollect < 0)
+ throw newIllegalArgumentException("wrong number of arguments");
+ MethodHandle res = MethodHandleImpl.collectArguments(target, newType, collectPos, null);
+ if (res == null) {
+ throw newIllegalArgumentException("cannot collect from "+newType+" to " +oldType);
+ }
+ return res;
+ }
+
+ /**
+ * Produces a method handle of the requested return type which returns the given
+ * constant value every time it is invoked.
+ * <p>
+ * Before the method handle is returned, the passed-in value is converted to the requested type.
+ * If the requested type is primitive, widening primitive conversions are attempted,
+ * else reference conversions are attempted.
+ * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)},
+ * unless the type is {@code void}, in which case it is {@code identity(type)}.
+ * @param type the return type of the desired method handle
+ * @param value the value to return
+ * @return a method handle of the given return type and no arguments, which always returns the given value
+ * @throws NullPointerException if the {@code type} argument is null
+ * @throws ClassCastException if the value cannot be converted to the required return type
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle constant(Class<?> type, Object value) {
+ if (type.isPrimitive()) {
+ if (type == void.class)
+ throw newIllegalArgumentException("void type");
+ Wrapper w = Wrapper.forPrimitiveType(type);
+ return identity(type).bindTo(w.convert(value, type));
+ } else {
+ return identity(type).bindTo(type.cast(value));
+ }
+ }
+
+ /**
+ * Produces a method handle which returns its sole argument when invoked.
+ * <p>The identity function for {@code void} takes no arguments and returns no values.
+ * @param type the type of the sole parameter and return value of the desired method handle
+ * @return a unary method handle which accepts and returns the given type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle identity(Class<?> type) {
+ if (type == void.class)
+ throw newIllegalArgumentException("void type");
+ else if (type == Object.class)
+ return ValueConversions.identity();
+ else if (type.isPrimitive())
+ return ValueConversions.identity(Wrapper.forPrimitiveType(type));
+ else
+ return AdapterMethodHandle.makeRetypeRaw(
+ MethodType.methodType(type, type), ValueConversions.identity());
+ }
+
+ /**
+ * Produces a method handle which calls the original method handle {@code target},
+ * after inserting the given argument(s) at the given position.
+ * The formal parameters to {@code target} which will be supplied by those
+ * arguments are called <em>bound parameters</em>, because the new method
+ * will contain bindings for those parameters take from {@code values}.
+ * The type of the new method handle will drop the types for the bound
+ * parameters from the original target type, since the new method handle
+ * will no longer require those arguments to be supplied by its callers.
+ * <p>
+ * Each given argument object must match the corresponding bound parameter type.
+ * If a bound parameter type is a primitive, the argument object
+ * must be a wrapper, and will be unboxed to produce the primitive value.
+ * <p>
+ * The <i>pos</i> may range between zero and <i>N</i> (inclusively),
+ * where <i>N</i> is the number of argument types in resulting method handle
+ * (after bound parameter types are dropped).
+ * @param target the method handle to invoke after the argument is inserted
+ * @param pos where to insert the argument (zero for the first)
+ * @param values the series of arguments to insert
+ * @return a method handle which inserts an additional argument,
+ * before calling the original method handle
+ * @throws NullPointerException if the {@code target} argument or the {@code values} array is null
+ * @see MethodHandle#bindTo
+ */
+ public static
+ MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
+ int insCount = values.length;
+ MethodType oldType = target.type();
+ int outargs = oldType.parameterCount();
+ int inargs = outargs - insCount;
+ if (inargs < 0)
+ throw newIllegalArgumentException("too many values to insert");
+ if (pos < 0 || pos > inargs)
+ throw newIllegalArgumentException("no argument type to append");
+ MethodHandle result = target;
+ for (int i = 0; i < insCount; i++) {
+ Object value = values[i];
+ Class<?> valueType = oldType.parameterType(pos+i);
+ value = checkValue(valueType, value);
+ if (pos == 0 && !valueType.isPrimitive()) {
+ // At least for now, make bound method handles a special case.
+ MethodHandle bmh = MethodHandleImpl.bindReceiver(result, value);
+ if (bmh != null) {
+ result = bmh;
+ continue;
+ }
+ // else fall through to general adapter machinery
+ }
+ result = MethodHandleImpl.bindArgument(result, pos, value);
+ }
+ return result;
+ }
+
+ /**
+ * Produces a method handle which calls the original method handle,
+ * after dropping the given argument(s) at the given position.
+ * The type of the new method handle will insert the given argument
+ * type(s), at that position, into the original handle's type.
+ * <p>
+ * The <i>pos</i> may range between zero and <i>N</i>,
+ * where <i>N</i> is the number of argument types in <i>target</i>,
+ * meaning to drop the first or last argument (respectively),
+ * or an argument somewhere in between.
+ * <p>
+ * <b>Example:</b>
+ * <p><blockquote><pre>
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
+MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
+assertEquals(bigType, d0.type());
+assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
+ * </pre></blockquote>
+ * <p>
+ * This method is also equivalent to the following code:
+ * <p><blockquote><pre>
+ * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}(target, pos, valueTypes.toArray(new Class[0]))
+ * </pre></blockquote>
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the {@code target} argument is null,
+ * or if the {@code valueTypes} list or any of its elements is null
+ * @throws IllegalArgumentException if any of the {@code valueTypes} is {@code void.class}
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
+ if (valueTypes.size() == 0) return target;
+ MethodType oldType = target.type();
+ int outargs = oldType.parameterCount();
+ int inargs = outargs + valueTypes.size();
+ if (pos < 0 || pos >= inargs)
+ throw newIllegalArgumentException("no argument type to remove");
+ ArrayList<Class<?>> ptypes =
+ new ArrayList<Class<?>>(oldType.parameterList());
+ ptypes.addAll(pos, valueTypes);
+ MethodType newType = MethodType.methodType(oldType.returnType(), ptypes);
+ return MethodHandleImpl.dropArguments(target, newType, pos);
+ }
+
+ /**
+ * Produces a method handle which calls the original method handle,
+ * after dropping the given argument(s) at the given position.
+ * The type of the new method handle will insert the given argument
+ * type(s), at that position, into the original handle's type.
+ * <p>
+ * The <i>pos</i> may range between zero and <i>N</i>,
+ * where <i>N</i> is the number of argument types in <i>target</i>,
+ * meaning to drop the first or last argument (respectively),
+ * or an argument somewhere in between.
+ * <p>
+ * <b>Example:</b>
+ * <p><blockquote><pre>
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle d0 = dropArguments(cat, 0, String.class);
+assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
+MethodHandle d1 = dropArguments(cat, 1, String.class);
+assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
+MethodHandle d2 = dropArguments(cat, 2, String.class);
+assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
+MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
+assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
+ * </pre></blockquote>
+ * <p>
+ * This method is also equivalent to the following code:
+ * <p><blockquote><pre>
+ * {@link #dropArguments(MethodHandle,int,List) dropArguments}(target, pos, Arrays.asList(valueTypes))
+ * </pre></blockquote>
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the {@code target} argument is null,
+ * or if the {@code valueTypes} array or any of its elements is null
+ * @throws IllegalArgumentException if any of the {@code valueTypes} is {@code void.class}
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
+ return dropArguments(target, pos, Arrays.asList(valueTypes));
+ }
+
+ /**
+ * Adapts a target method handle {@code target} by pre-processing
+ * one or more of its arguments, each with its own unary filter function,
+ * and then calling the target with each pre-processed argument
+ * replaced by the result of its corresponding filter function.
+ * <p>
+ * The pre-processing is performed by one or more method handles,
+ * specified in the elements of the {@code filters} array.
+ * Null arguments in the array are ignored, and the corresponding arguments left unchanged.
+ * (If there are no non-null elements in the array, the original target is returned.)
+ * Each filter is applied to the corresponding argument of the adapter.
+ * <p>
+ * If a filter {@code F} applies to the {@code N}th argument of
+ * the method handle, then {@code F} must be a method handle which
+ * takes exactly one argument. The type of {@code F}'s sole argument
+ * replaces the corresponding argument type of the target
+ * in the resulting adapted method handle.
+ * The return type of {@code F} must be identical to the corresponding
+ * parameter type of the target.
+ * <p>
+ * It is an error if there are elements of {@code filters}
+ * which do not correspond to argument positions in the target.
+ * <b>Example:</b>
+ * <p><blockquote><pre>
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle upcase = lookup().findVirtual(String.class,
+ "toUpperCase", methodType(String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle f0 = filterArguments(cat, 0, upcase);
+assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
+MethodHandle f1 = filterArguments(cat, 1, upcase);
+assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
+MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
+assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
+ * </pre></blockquote>
+ *
+ * @param target the method handle to invoke after arguments are filtered
+ * @param pos the position of the first argument to filter
+ * @param filters method handles to call initially on filtered arguments
+ * @return method handle which incorporates the specified argument filtering logic
+ * @throws NullPointerException if the {@code target} argument is null
+ * or if the {@code filters} array is null
+ * @throws IllegalArgumentException if a non-null element of {@code filters}
+ * does not match a corresponding argument type of {@code target} as described above,
+ * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()}
+ */
+ public static
+ MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
+ MethodType targetType = target.type();
+ MethodHandle adapter = target;
+ MethodType adapterType = targetType;
+ int maxPos = targetType.parameterCount();
+ if (pos + filters.length > maxPos)
+ throw newIllegalArgumentException("too many filters");
+ int curPos = pos-1; // pre-incremented
+ for (MethodHandle filter : filters) {
+ curPos += 1;
+ if (filter == null) continue; // ignore null elements of filters
+ MethodType filterType = filter.type();
+ if (filterType.parameterCount() != 1
+ || filterType.returnType() != targetType.parameterType(curPos))
+ throw newIllegalArgumentException("target and filter types do not match");
+ adapterType = adapterType.changeParameterType(curPos, filterType.parameterType(0));
+ adapter = MethodHandleImpl.filterArgument(adapter, curPos, filter);
+ }
+ MethodType midType = adapter.type();
+ if (midType != adapterType)
+ adapter = MethodHandleImpl.convertArguments(adapter, adapterType, midType, null);
+ return adapter;
+ }
+
+ /**
+ * Adapts a target method handle {@code target} by post-processing
+ * its return value with a unary filter function.
+ * <p>
+ * If a filter {@code F} applies to the return value of
+ * the target method handle, then {@code F} must be a method handle which
+ * takes exactly one argument. The return type of {@code F}
+ * replaces the return type of the target
+ * in the resulting adapted method handle.
+ * The argument type of {@code F} must be identical to the
+ * return type of the target.
+ * <b>Example:</b>
+ * <p><blockquote><pre>
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle length = lookup().findVirtual(String.class,
+ "length", methodType(int.class));
+System.out.println((String) cat.invokeExact("x", "y")); // xy
+MethodHandle f0 = filterReturnValue(cat, length);
+System.out.println((int) f0.invokeExact("x", "y")); // 2
+ * </pre></blockquote>
+ * @param target the method handle to invoke before filtering the return value
+ * @param filter method handle to call on the return value
+ * @return method handle which incorporates the specified return value filtering logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if {@code filter}
+ * does not match the return type of {@code target} as described above
+ */
+ public static
+ MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ if (filterType.parameterCount() != 1
+ || filterType.parameterType(0) != targetType.returnType())
+ throw newIllegalArgumentException("target and filter types do not match");
+ // result = fold( lambda(retval, arg...) { filter(retval) },
+ // lambda( arg...) { target(arg...) } )
+ // FIXME: Too many nodes here.
+ MethodHandle returner = dropArguments(filter, 1, targetType.parameterList());
+ return foldArguments(returner, target);
+ }
+
+ /**
+ * Adapts a target method handle {@code target} by pre-processing
+ * some of its arguments, and then calling the target with
+ * the result of the pre-processing, plus all original arguments.
+ * <p>
+ * The pre-processing is performed by a second method handle, the {@code combiner}.
+ * The first {@code N} arguments passed to the adapter,
+ * are copied to the combiner, which then produces a result.
+ * (Here, {@code N} is defined as the parameter count of the adapter.)
+ * After this, control passes to the {@code target}, with both the result
+ * of the combiner, and all the original incoming arguments.
+ * <p>
+ * The first argument type of the target must be identical with the
+ * return type of the combiner.
+ * The resulting adapter is the same type as the target, except that the
+ * initial argument type of the target is dropped.
+ * <p>
+ * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
+ * that either the {@code combiner} or {@code target} does not wish to receive.
+ * If some of the incoming arguments are destined only for the combiner,
+ * consider using {@link MethodHandle#asCollector asCollector} instead, since those
+ * arguments will not need to be live on the stack on entry to the
+ * target.)
+ * <p>
+ * The first argument of the target must be identical with the
+ * return value of the combiner.
+ * <p> Here is pseudocode for the resulting adapter:
+ * <blockquote><pre>
+ * // there are N arguments in the A sequence
+ * T target(V, A[N]..., B...);
+ * V combiner(A...);
+ * T adapter(A... a, B... b) {
+ * V v = combiner(a...);
+ * return target(v, a..., b...);
+ * }
+ * </pre></blockquote>
+ * @param target the method handle to invoke after arguments are combined
+ * @param combiner method handle to call initially on the incoming arguments
+ * @return method handle which incorporates the specified argument folding logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the first argument type of
+ * {@code target} is not the same as {@code combiner}'s return type,
+ * or if the following argument types of {@code target}
+ * are not identical with the argument types of {@code combiner}
+ */
+ public static
+ MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
+ MethodType targetType = target.type();
+ MethodType combinerType = combiner.type();
+ int foldArgs = combinerType.parameterCount();
+ boolean ok = (targetType.parameterCount() >= 1 + foldArgs);
+ if (ok && !combinerType.parameterList().equals(targetType.parameterList().subList(1, foldArgs+1)))
+ ok = false;
+ if (ok && !combinerType.returnType().equals(targetType.parameterType(0)))
+ ok = false;
+ if (!ok)
+ throw misMatchedTypes("target and combiner types", targetType, combinerType);
+ MethodType newType = targetType.dropParameterTypes(0, 1);
+ return MethodHandleImpl.foldArguments(target, newType, combiner);
+ }
+
+ /**
+ * Makes a method handle which adapts a target method handle,
+ * by guarding it with a test, a boolean-valued method handle.
+ * If the guard fails, a fallback handle is called instead.
+ * All three method handles must have the same corresponding
+ * argument and return types, except that the return type
+ * of the test must be boolean, and the test is allowed
+ * to have fewer arguments than the other two method handles.
+ * <p> Here is pseudocode for the resulting adapter:
+ * <blockquote><pre>
+ * boolean test(A...);
+ * T target(A...,B...);
+ * T fallback(A...,B...);
+ * T adapter(A... a,B... b) {
+ * if (test(a...))
+ * return target(a..., b...);
+ * else
+ * return fallback(a..., b...);
+ * }
+ * </pre></blockquote>
+ * Note that the test arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the test, and so are passed unchanged
+ * from the caller to the target or fallback as appropriate.
+ * @param test method handle used for test, must return boolean
+ * @param target method handle to call if test passes
+ * @param fallback method handle to call if test fails
+ * @return method handle which incorporates the specified if/then/else logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code test} does not return boolean,
+ * or if all three method types do not match (with the return
+ * type of {@code test} changed to match that of {@code target}).
+ */
+ public static
+ MethodHandle guardWithTest(MethodHandle test,
+ MethodHandle target,
+ MethodHandle fallback) {
+ MethodType gtype = test.type();
+ MethodType ttype = target.type();
+ MethodType ftype = fallback.type();
+ if (!ttype.equals(ftype))
+ throw misMatchedTypes("target and fallback types", ttype, ftype);
+ if (gtype.returnType() != boolean.class)
+ throw newIllegalArgumentException("guard type is not a predicate "+gtype);
+ List<Class<?>> targs = ttype.parameterList();
+ List<Class<?>> gargs = gtype.parameterList();
+ if (!targs.equals(gargs)) {
+ int gpc = gargs.size(), tpc = targs.size();
+ if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
+ throw misMatchedTypes("target and test types", ttype, gtype);
+ test = dropArguments(test, gpc, targs.subList(gpc, tpc));
+ gtype = test.type();
+ }
+ return MethodHandleImpl.makeGuardWithTest(test, target, fallback);
+ }
+
+ static RuntimeException misMatchedTypes(String what, MethodType t1, MethodType t2) {
+ return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
+ }
+
+ /**
+ * Makes a method handle which adapts a target method handle,
+ * by running it inside an exception handler.
+ * If the target returns normally, the adapter returns that value.
+ * If an exception matching the specified type is thrown, the fallback
+ * handle is called instead on the exception, plus the original arguments.
+ * <p>
+ * The target and handler must have the same corresponding
+ * argument and return types, except that handler may omit trailing arguments
+ * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
+ * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
+ * <p> Here is pseudocode for the resulting adapter:
+ * <blockquote><pre>
+ * T target(A..., B...);
+ * T handler(ExType, A...);
+ * T adapter(A... a, B... b) {
+ * try {
+ * return target(a..., b...);
+ * } catch (ExType ex) {
+ * return handler(ex, a...);
+ * }
+ * }
+ * </pre></blockquote>
+ * Note that the saved arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the target, and so are passed unchanged
+ * from the caller to the handler, if the handler is invoked.
+ * <p>
+ * The target and handler must return the same type, even if the handler
+ * always throws. (This might happen, for instance, because the handler
+ * is simulating a {@code finally} clause).
+ * To create such a throwing handler, compose the handler creation logic
+ * with {@link #throwException throwException},
+ * in order to create a method handle of the correct return type.
+ * @param target method handle to call
+ * @param exType the type of exception which the handler will catch
+ * @param handler method handle to call if a matching exception is thrown
+ * @return method handle which incorporates the specified try/catch logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code handler} does not accept
+ * the given exception type, or if the method handle types do
+ * not match in their return types and their
+ * corresponding parameters
+ */
+ public static
+ MethodHandle catchException(MethodHandle target,
+ Class<? extends Throwable> exType,
+ MethodHandle handler) {
+ MethodType ttype = target.type();
+ MethodType htype = handler.type();
+ if (htype.parameterCount() < 1 ||
+ !htype.parameterType(0).isAssignableFrom(exType))
+ throw newIllegalArgumentException("handler does not accept exception type "+exType);
+ if (htype.returnType() != ttype.returnType())
+ throw misMatchedTypes("target and handler return types", ttype, htype);
+ List<Class<?>> targs = ttype.parameterList();
+ List<Class<?>> hargs = htype.parameterList();
+ hargs = hargs.subList(1, hargs.size()); // omit leading parameter from handler
+ if (!targs.equals(hargs)) {
+ int hpc = hargs.size(), tpc = targs.size();
+ if (hpc >= tpc || !targs.subList(0, hpc).equals(hargs))
+ throw misMatchedTypes("target and handler types", ttype, htype);
+ handler = dropArguments(handler, hpc, hargs.subList(hpc, tpc));
+ htype = handler.type();
+ }
+ return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
+ }
+
+ /**
+ * Produces a method handle which will throw exceptions of the given {@code exType}.
+ * The method handle will accept a single argument of {@code exType},
+ * and immediately throw it as an exception.
+ * The method type will nominally specify a return of {@code returnType}.
+ * The return type may be anything convenient: It doesn't matter to the
+ * method handle's behavior, since it will never return normally.
+ * @return method handle which can throw the given exceptions
+ * @throws NullPointerException if either argument is null
+ */
+ public static
+ MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
+ return MethodHandleImpl.throwException(MethodType.methodType(returnType, exType));
+ }
+
+ /**
+ * Produces an instance of the given single-method interface which redirects
+ * its calls to the given method handle.
+ * <p>
+ * A single-method interface is an interface which declares a unique method.
+ * When determining the unique method of a single-method interface,
+ * the public {@code Object} methods ({@code toString}, {@code equals}, {@code hashCode})
+ * are disregarded. For example, {@link java.util.Comparator} is a single-method interface,
+ * even though it re-declares the {@code Object.equals} method.
+ * <p>
+ * The type must be public. No additional access checks are performed.
+ * <p>
+ * The resulting instance of the required type will respond to
+ * invocation of the type's single abstract method by calling
+ * the given {@code target} on the incoming arguments,
+ * and returning or throwing whatever the {@code target}
+ * returns or throws. The invocation will be as if by
+ * {@code target.invokeGeneric}.
+ * The target's type will be checked before the
+ * instance is created, as if by a call to {@code asType},
+ * which may result in a {@code WrongMethodTypeException}.
+ * <p>
+ * The wrapper instance will implement the requested interface
+ * and its super-types, but no other single-method interfaces.
+ * This means that the instance will not unexpectedly
+ * pass an {@code instanceof} test for any unrequested type.
+ * <p style="font-size:smaller;">
+ * <em>Implementation Note:</em>
+ * Therefore, each instance must implement a unique single-method interface.
+ * Implementations may not bundle together
+ * multiple single-method interfaces onto single implementation classes
+ * in the style of {@link java.awt.AWTEventMulticaster}.
+ * <p>
+ * The method handle may throw an <em>undeclared exception</em>,
+ * which means any checked exception (or other checked throwable)
+ * not declared by the requested type's single abstract method.
+ * If this happens, the throwable will be wrapped in an instance of
+ * {@link java.lang.reflect.UndeclaredThrowableException UndeclaredThrowableException}
+ * and thrown in that wrapped form.
+ * <p>
+ * Like {@link java.lang.Integer#valueOf Integer.valueOf},
+ * {@code asInstance} is a factory method whose results are defined
+ * by their behavior.
+ * It is not guaranteed to return a new instance for every call.
+ * <p>
+ * Because of the possibility of {@linkplain java.lang.reflect.Method#isBridge bridge methods}
+ * and other corner cases, the interface may also have several abstract methods
+ * with the same name but having distinct descriptors (types of returns and parameters).
+ * In this case, all the methods are bound in common to the one given {@code target}.
+ * The type check and effective {@code asType} conversion is applied to each
+ * method type descriptor, and all abstract methods are bound to the {@code target} in common.
+ * Beyond this type check, no further checks are made to determine that the
+ * abstract methods are related in any way.
+ * <p>
+ * Future versions of this API may accept additional types,
+ * such as abstract classes with single abstract methods.
+ * Future versions of this API may also equip wrapper instances
+ * with one or more additional public "marker" interfaces.
+ *
+ * @param target the method handle to invoke from the wrapper
+ * @param smType the desired type of the wrapper, a single-method interface
+ * @return a correctly-typed wrapper for the given {@code target}
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the {@code smType} is not a
+ * valid argument to this method
+ * @throws WrongMethodTypeException if the {@code target} cannot
+ * be converted to the type required by the requested interface
+ */
+ // Other notes to implementors:
+ // <p>
+ // No stable mapping is promised between the single-method interface and
+ // the implementation class C. Over time, several implementation
+ // classes might be used for the same type.
+ // <p>
+ // If the implementation is able
+ // to prove that a wrapper of the required type
+ // has already been created for a given
+ // method handle, or for another method handle with the
+ // same behavior, the implementation may return that wrapper in place of
+ // a new wrapper.
+ // <p>
+ // This method is designed to apply to common use cases
+ // where a single method handle must interoperate with
+ // an interface that implements a function-like
+ // API. Additional variations, such as single-abstract-method classes with
+ // private constructors, or interfaces with multiple but related
+ // entry points, must be covered by hand-written or automatically
+ // generated adapter classes.
+ //
+ public static
+ <T> T asInstance(final MethodHandle target, final Class<T> smType) {
+ // POC implementation only; violates the above contract several ways
+ final Method sm = getSingleMethod(smType);
+ if (sm == null)
+ throw new IllegalArgumentException("not a single-method interface: "+smType.getName());
+ MethodType smMT = MethodType.methodType(sm.getReturnType(), sm.getParameterTypes());
+ MethodHandle checkTarget = target.asType(smMT); // make throw WMT
+ checkTarget = checkTarget.asType(checkTarget.type().changeReturnType(Object.class));
+ final MethodHandle vaTarget = checkTarget.asSpreader(Object[].class, smMT.parameterCount());
+ return smType.cast(Proxy.newProxyInstance(
+ smType.getClassLoader(),
+ new Class[]{ smType, WrapperInstance.class },
+ new InvocationHandler() {
+ private Object getArg(String name) {
+ if ((Object)name == "getWrapperInstanceTarget") return target;
+ if ((Object)name == "getWrapperInstanceType") return smType;
+ throw new AssertionError();
+ }
+ public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
+ if (method.getDeclaringClass() == WrapperInstance.class)
+ return getArg(method.getName());
+ if (method.equals(sm))
+ return vaTarget.invokeExact(args);
+ if (isObjectMethod(method))
+ return callObjectMethod(this, method, args);
+ throw new InternalError();
+ }
+ }));
+ }
+
+ /**
+ * Determines if the given object was produced by a call to {@link #asInstance asInstance}.
+ * @param x any reference
+ * @return true if the reference is not null and points to an object produced by {@code asInstance}
+ */
+ public static
+ boolean isWrapperInstance(Object x) {
+ return x instanceof WrapperInstance;
+ }
+
+ private static WrapperInstance asWrapperInstance(Object x) {
+ try {
+ if (x != null)
+ return (WrapperInstance) x;
+ } catch (ClassCastException ex) {
+ }
+ throw new IllegalArgumentException("not a wrapper instance");
+ }
+
+ /**
+ * Produces or recovers a target method handle which is behaviorally
+ * equivalent to the unique method of this wrapper instance.
+ * The object {@code x} must have been produced by a call to {@link #asInstance asInstance}.
+ * This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.
+ * @param x any reference
+ * @return a method handle implementing the unique method
+ * @throws IllegalArgumentException if the reference x is not to a wrapper instance
+ */
+ public static
+ MethodHandle wrapperInstanceTarget(Object x) {
+ return asWrapperInstance(x).getWrapperInstanceTarget();
+ }
+
+ /**
+ * Recovers the unique single-method interface type for which this wrapper instance was created.
+ * The object {@code x} must have been produced by a call to {@link #asInstance asInstance}.
+ * This requirement may be tested via {@link #isWrapperInstance isWrapperInstance}.
+ * @param x any reference
+ * @return the single-method interface type for which the wrapper was created
+ * @throws IllegalArgumentException if the reference x is not to a wrapper instance
+ */
+ public static
+ Class<?> wrapperInstanceType(Object x) {
+ return asWrapperInstance(x).getWrapperInstanceType();
+ }
+
+ private static
+ boolean isObjectMethod(Method m) {
+ switch (m.getName()) {
+ case "toString":
+ return (m.getReturnType() == String.class
+ && m.getParameterTypes().length == 0);
+ case "hashCode":
+ return (m.getReturnType() == int.class
+ && m.getParameterTypes().length == 0);
+ case "equals":
+ return (m.getReturnType() == boolean.class
+ && m.getParameterTypes().length == 1
+ && m.getParameterTypes()[0] == Object.class);
+ }
+ return false;
+ }
+
+ private static
+ Object callObjectMethod(Object self, Method m, Object[] args) {
+ assert(isObjectMethod(m)) : m;
+ switch (m.getName()) {
+ case "toString":
+ return self.getClass().getName() + "@" + Integer.toHexString(self.hashCode());
+ case "hashCode":
+ return System.identityHashCode(self);
+ case "equals":
+ return (self == args[0]);
+ }
+ return null;
+ }
+
+ private static
+ Method getSingleMethod(Class<?> smType) {
+ Method sm = null;
+ for (Method m : smType.getMethods()) {
+ int mod = m.getModifiers();
+ if (Modifier.isAbstract(mod)) {
+ if (sm != null && !isObjectMethod(sm))
+ return null; // too many abstract methods
+ sm = m;
+ }
+ }
+ if (!smType.isInterface() && getSingleConstructor(smType) == null)
+ return null; // wrong kind of constructor
+ return sm;
+ }
+
+ private static
+ Constructor getSingleConstructor(Class<?> smType) {
+ for (Constructor c : smType.getDeclaredConstructors()) {
+ if (c.getParameterTypes().length == 0) {
+ int mod = c.getModifiers();
+ if (Modifier.isPublic(mod) || Modifier.isProtected(mod))
+ return c;
+ }
+ }
+ return null;
+ }
+
+ /*non-public*/
+ static MethodHandle asVarargsCollector(MethodHandle target, Class<?> arrayType) {
+ return MethodHandleImpl.asVarargsCollector(target, arrayType);
+ }
+}