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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN">
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<HTML>
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<HEAD>
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<!--
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Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
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DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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This code is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License version 2 only, as
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published by the Free Software Foundation. Sun designates this
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particular file as subject to the "Classpath" exception as provided
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by Sun in the LICENSE file that accompanied this code.
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This code is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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version 2 for more details (a copy is included in the LICENSE file that
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accompanied this code).
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You should have received a copy of the GNU General Public License version
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2 along with this work; if not, write to the Free Software Foundation,
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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CA 95054 USA or visit www.sun.com if you need additional information or
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have any questions.
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-->
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</HEAD>
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<BODY BGCOLOR="white">
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<P>
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<B> Licensee impact of JDK 1.4 reflection changes </B>
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</P>
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<P>
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Sun's JDK 1.4 contains a new implementation of java.lang.reflect which
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offers substantially higher performance than previous JDKs' native
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code. Licensees can at their discretion port these changes. There are
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no public API or documentation changes associated with the new
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reflection implementation aside from a few minor clarifications in the
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specifications of Method.invoke(), Constructor.newInstance(), and a
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few methods in java.lang.reflect.Field.
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</P>
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<P>
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The bulk of the new implementation is Java programming language code
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which generates bytecodes, and is therefore portable. If licensees
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desire to port it, the following JVM changes are required:
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<OL>
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<LI> The following four new JVM entry points must be added:
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<UL>
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<LI> JVM_GetClassDeclaredConstructors
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<LI> JVM_GetClassDeclaredFields
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<LI> JVM_GetClassDeclaredMethods
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<LI> JVM_GetClassAccessFlags
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</UL>
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The first three return the declared constructors, fields, and methods
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for a given class, with an option to return only the public ones. They
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are similar in functionality to the earlier GetClassConstructors,
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GetClassFields, and GetClassMethods. JVM_GetClassDeclaredFields and
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JVM_GetClassDeclaredMethods must intern the Strings for the names of
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the Field and Method objects returned. The fouth returns the access
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flags for a given class as marked in the class file, as opposed to in
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the InnerClasses attribute if the class is an inner class, and
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therefore differs from JVM_GetClassModifiers for inner classes (most
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importantly, protected inner classes; see 4471811.)
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<LI> The JVM's link resolver must be modified to allow all field and
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method references from subclasses of sun.reflect.MagicAccessorImpl to
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any other class (even to private members of other classes) to
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succeed. This allows setAccessible() and its associated checks to be
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implemented in Java.
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<LI> The code which calls the verifier must skip verification for all
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subclasses of sun.reflect.MagicAccessorImpl. (It was originally
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intended that only a subset of the stub classes used for serialization
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would not pass the verifier, specifically, those subclassing
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SerializationConstructorAccessorImpl; see 4486457 for a case where
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this does not work.)
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<LI> The stack walker for security checks must be modified to skip not
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only all Method.invoke() frames, but also any frames for which the
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class is a subclass of sun.reflect.MethodAccessorImpl.
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<LI> The JVM entry points JVM_InvokeMethod and
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JVM_NewInstanceFromConstructor are currently still used because the
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first invocation of the bytecode-based reflection is currently slower
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than the original native code. The security checks they perform can,
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however, be disabled, as they are now performed by Java programming
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language code.
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</OL>
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</P>
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<P>
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The following changes were discovered to be necessary for backward
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compatibility with certain applications (see bug 4474172):
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<OL>
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<LI> The existing JVM entry point JVM_LatestUserDefinedLoader
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(typically used in applications which rely on the 1.1 security
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framework) must skip reflection-related frames in its stack walk:
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specifically all frames associated with subclasses of
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sun.reflect.MethodAccessorImpl and
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sun.reflect.ConstructorAccessorImpl.
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<LI> The new reflection implementation can cause class loading to
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occur in previously-unexpected places (namely during reflective
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calls). This can cause class loaders which contain subtle bugs to
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break. In general it is not possible to guarantee complete backward
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bug compatibility, but one kind of bug has been observed more than
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once: the inability of a user-defined loader to handle delegation to
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it for a class it has already loaded. The new reflection
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implementation is predicated on delegation working properly, as it
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loads stub classes into newly-fabricated class loaders of type
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sun.reflect.DelegatingClassLoader, one stub class per loader, to allow
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unloading of the stub classes to occur more quickly. To handle this
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kind of bug, the JVM's internal class lookup mechanism must be
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slightly modified to check for instances of
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sun.reflect.DelegatingClassLoader as the incoming class loader and
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silently traverse the "parent" field once for such loaders before
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entering the bulk of the resolution code. This avoids an upcall to
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Java programming language code which certain loaders can not handle.
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</OL>
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</P>
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<P>
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The following JVM entry points may be deleted:
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<UL>
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<LI> JVM_GetClassFields
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<LI> JVM_GetClassMethods
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<LI> JVM_GetClassConstructors
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<LI> JVM_GetClassField
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<LI> JVM_GetClassMethod
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<LI> JVM_GetClassConstructor
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<LI> JVM_NewInstance
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<LI> JVM_GetField
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<LI> JVM_GetPrimitiveField
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<LI> JVM_SetField
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<LI> JVM_SetPrimitiveField
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</UL>
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</P>
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<P>
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To keep using the previous reflection implementation, licensees should
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not take changes from Sun's JDK 1.4 relating specifically to the
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implementation of reflection in the following classes/methods and
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any associated native code:
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<UL>
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<LI> java.lang.Class.newInstance0
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<LI> java.lang.Class.getClassLoader0
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<LI> java.lang.Class.getFields
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<LI> java.lang.Class.getMethods
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<LI> java.lang.Class.getDeclaredFields
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<LI> java.lang.Class.getDeclaredMethods
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<LI> java.lang.Class.getFields0
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<LI> java.lang.Class.getMethods0
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<LI> java.lang.Class.getConstructors0
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<LI> java.lang.Class.getField0
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<LI> java.lang.Class.getMethod0
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<LI> java.lang.Class.getConstructor0
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<LI> java.lang.ClassLoader.getCallerClassLoader
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<LI> java.lang.System.getCallerClass
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<LI> java.lang.reflect.AccessibleObject
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<LI> java.lang.reflect.Constructor
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<LI> java.lang.reflect.Field
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<LI> java.lang.reflect.Method
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<LI> java.lang.reflect.Modifier
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<LI> sun.misc.ClassReflector
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</UL>
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</P>
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</HTML>
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