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/*
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* Copyright 2000-2007 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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*
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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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*
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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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*
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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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*
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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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package java.beans;
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import java.util.Collections;
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import java.util.HashMap;
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import java.util.IdentityHashMap;
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import java.util.Map;
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/**
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* An <code>Encoder</code> is a class which can be used to create
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* files or streams that encode the state of a collection of
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* JavaBeans in terms of their public APIs. The <code>Encoder</code>,
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* in conjunction with its persistence delegates, is responsible for
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* breaking the object graph down into a series of <code>Statements</code>s
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* and <code>Expression</code>s which can be used to create it.
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* A subclass typically provides a syntax for these expressions
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* using some human readable form - like Java source code or XML.
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*
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* @since 1.4
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*
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* @author Philip Milne
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*/
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public class Encoder {
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private final Map<Class<?>, PersistenceDelegate> delegates
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= Collections.synchronizedMap(new HashMap<Class<?>, PersistenceDelegate>());
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private Map bindings = new IdentityHashMap();
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private ExceptionListener exceptionListener;
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boolean executeStatements = true;
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private Map attributes;
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/**
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* Write the specified object to the output stream.
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* The serialized form will denote a series of
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* expressions, the combined effect of which will create
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* an equivalent object when the input stream is read.
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* By default, the object is assumed to be a <em>JavaBean</em>
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* with a nullary constructor, whose state is defined by
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* the matching pairs of "setter" and "getter" methods
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* returned by the Introspector.
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*
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* @param o The object to be written to the stream.
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*
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* @see XMLDecoder#readObject
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*/
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protected void writeObject(Object o) {
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if (o == this) {
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return;
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}
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PersistenceDelegate info = getPersistenceDelegate(o == null ? null : o.getClass());
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info.writeObject(o, this);
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}
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/**
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* Sets the exception handler for this stream to <code>exceptionListener</code>.
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* The exception handler is notified when this stream catches recoverable
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* exceptions.
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*
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* @param exceptionListener The exception handler for this stream;
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* if <code>null</code> the default exception listener will be used.
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*
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* @see #getExceptionListener
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*/
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public void setExceptionListener(ExceptionListener exceptionListener) {
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this.exceptionListener = exceptionListener;
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}
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/**
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* Gets the exception handler for this stream.
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*
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* @return The exception handler for this stream;
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* Will return the default exception listener if this has not explicitly been set.
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*
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* @see #setExceptionListener
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*/
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public ExceptionListener getExceptionListener() {
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return (exceptionListener != null) ? exceptionListener : Statement.defaultExceptionListener;
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}
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Object getValue(Expression exp) {
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try {
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return (exp == null) ? null : exp.getValue();
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}
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catch (Exception e) {
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getExceptionListener().exceptionThrown(e);
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throw new RuntimeException("failed to evaluate: " + exp.toString());
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}
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}
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/**
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* Returns the persistence delegate for the given type.
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* The persistence delegate is calculated
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* by applying the following of rules in order:
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* <ul>
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* <li>
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* If the type is an array, an internal persistence
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* delegate is returned which will instantiate an
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* array of the appropriate type and length, initializing
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* each of its elements as if they are properties.
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* <li>
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* If the type is a proxy, an internal persistence
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* delegate is returned which will instantiate a
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* new proxy instance using the static
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* "newProxyInstance" method defined in the
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* Proxy class.
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* <li>
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* If the BeanInfo for this type has a <code>BeanDescriptor</code>
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* which defined a "persistenceDelegate" property, this
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* value is returned.
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* <li>
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* In all other cases the default persistence delegate
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* is returned. The default persistence delegate assumes
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* the type is a <em>JavaBean</em>, implying that it has a default constructor
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* and that its state may be characterized by the matching pairs
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* of "setter" and "getter" methods returned by the Introspector.
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* The default constructor is the constructor with the greatest number
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* of parameters that has the {@link ConstructorProperties} annotation.
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* If none of the constructors have the {@code ConstructorProperties} annotation,
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* then the nullary constructor (constructor with no parameters) will be used.
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* For example, in the following the nullary constructor
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* for {@code Foo} will be used, while the two parameter constructor
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* for {@code Bar} will be used.
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* <code>
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* public class Foo {
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* public Foo() { ... }
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* public Foo(int x) { ... }
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* }
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* public class Bar {
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* public Bar() { ... }
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* @ConstructorProperties({"x"})
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* public Bar(int x) { ... }
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* @ConstructorProperties({"x", "y"})
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* public Bar(int x, int y) { ... }
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* }
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* </code>
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* </ul>
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*
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* @param type The type of the object.
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* @return The persistence delegate for this type of object.
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*
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* @see #setPersistenceDelegate
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* @see java.beans.Introspector#getBeanInfo
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* @see java.beans.BeanInfo#getBeanDescriptor
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*/
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public PersistenceDelegate getPersistenceDelegate(Class<?> type) {
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PersistenceDelegate pd = this.delegates.get(type);
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return (pd != null) ? pd : MetaData.getPersistenceDelegate(type);
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}
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/**
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* Sets the persistence delegate associated with this <code>type</code> to
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* <code>persistenceDelegate</code>.
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*
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* @param type The class of objects that <code>persistenceDelegate</code> applies to.
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* @param persistenceDelegate The persistence delegate for instances of <code>type</code>.
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*
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* @see #getPersistenceDelegate
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* @see java.beans.Introspector#getBeanInfo
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* @see java.beans.BeanInfo#getBeanDescriptor
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*/
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public void setPersistenceDelegate(Class<?> type,
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PersistenceDelegate persistenceDelegate)
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{
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if (persistenceDelegate != null) {
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this.delegates.put(type, persistenceDelegate);
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} else {
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this.delegates.remove(type);
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}
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}
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/**
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* Removes the entry for this instance, returning the old entry.
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*
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* @param oldInstance The entry that should be removed.
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* @return The entry that was removed.
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*
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* @see #get
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*/
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public Object remove(Object oldInstance) {
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Expression exp = (Expression)bindings.remove(oldInstance);
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return getValue(exp);
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}
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/**
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* Returns a tentative value for <code>oldInstance</code> in
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* the environment created by this stream. A persistence
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* delegate can use its <code>mutatesTo</code> method to
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* determine whether this value may be initialized to
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* form the equivalent object at the output or whether
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* a new object must be instantiated afresh. If the
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* stream has not yet seen this value, null is returned.
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*
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* @param oldInstance The instance to be looked up.
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* @return The object, null if the object has not been seen before.
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*/
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public Object get(Object oldInstance) {
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if (oldInstance == null || oldInstance == this ||
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oldInstance.getClass() == String.class) {
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return oldInstance;
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}
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Expression exp = (Expression)bindings.get(oldInstance);
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return getValue(exp);
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}
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private Object writeObject1(Object oldInstance) {
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Object o = get(oldInstance);
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if (o == null) {
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writeObject(oldInstance);
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o = get(oldInstance);
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}
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return o;
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}
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private Statement cloneStatement(Statement oldExp) {
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Object oldTarget = oldExp.getTarget();
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Object newTarget = writeObject1(oldTarget);
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Object[] oldArgs = oldExp.getArguments();
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Object[] newArgs = new Object[oldArgs.length];
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for (int i = 0; i < oldArgs.length; i++) {
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newArgs[i] = writeObject1(oldArgs[i]);
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}
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if (oldExp.getClass() == Statement.class) {
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return new Statement(newTarget, oldExp.getMethodName(), newArgs);
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}
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else {
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return new Expression(newTarget, oldExp.getMethodName(), newArgs);
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}
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}
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/**
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* Writes statement <code>oldStm</code> to the stream.
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* The <code>oldStm</code> should be written entirely
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* in terms of the callers environment, i.e. the
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* target and all arguments should be part of the
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* object graph being written. These expressions
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* represent a series of "what happened" expressions
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* which tell the output stream how to produce an
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* object graph like the original.
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* <p>
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* The implementation of this method will produce
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* a second expression to represent the same expression in
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* an environment that will exist when the stream is read.
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* This is achieved simply by calling <code>writeObject</code>
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* on the target and all the arguments and building a new
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* expression with the results.
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*
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* @param oldStm The expression to be written to the stream.
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*/
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public void writeStatement(Statement oldStm) {
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// System.out.println("writeStatement: " + oldExp);
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Statement newStm = cloneStatement(oldStm);
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if (oldStm.getTarget() != this && executeStatements) {
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try {
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newStm.execute();
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} catch (Exception e) {
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getExceptionListener().exceptionThrown(new Exception("Encoder: discarding statement "
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+ newStm, e));
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}
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}
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}
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/**
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* The implementation first checks to see if an
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* expression with this value has already been written.
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* If not, the expression is cloned, using
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* the same procedure as <code>writeStatement</code>,
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* and the value of this expression is reconciled
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* with the value of the cloned expression
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* by calling <code>writeObject</code>.
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*
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* @param oldExp The expression to be written to the stream.
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*/
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public void writeExpression(Expression oldExp) {
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// System.out.println("Encoder::writeExpression: " + oldExp);
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Object oldValue = getValue(oldExp);
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if (get(oldValue) != null) {
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return;
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}
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bindings.put(oldValue, (Expression)cloneStatement(oldExp));
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writeObject(oldValue);
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}
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void clear() {
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bindings.clear();
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}
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// Package private method for setting an attributes table for the encoder
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void setAttribute(Object key, Object value) {
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if (attributes == null) {
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attributes = new HashMap();
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}
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attributes.put(key, value);
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}
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Object getAttribute(Object key) {
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if (attributes == null) {
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return null;
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}
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return attributes.get(key);
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}
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}
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