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My first initial commit with all of mine experimental changes.

Dmitry Kabak (userdima committed 13 years ago

Commit d37b88d1 parent 3f5b46618352 files · +2598093 −-8690Browse files

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1+/*
2+ * Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
3+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4+ *
5+ * This code is free software; you can redistribute it and/or modify it
6+ * under the terms of the GNU General Public License version 2 only, as
7+ * published by the Free Software Foundation. Oracle designates this
8+ * particular file as subject to the "Classpath" exception as provided
9+ * by Oracle in the LICENSE file that accompanied this code.
10+ *
11+ * This code is distributed in the hope that it will be useful, but WITHOUT
12+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14+ * version 2 for more details (a copy is included in the LICENSE file that
15+ * accompanied this code).
16+ *
17+ * You should have received a copy of the GNU General Public License version
18+ * 2 along with this work; if not, write to the Free Software Foundation,
19+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20+ *
21+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22+ * or visit www.oracle.com if you need additional information or have any
23+ * questions.
24+ */
25+package java.beans;
26+
27+/**
28+ * The PersistenceDelegate class takes the responsibility
29+ * for expressing the state of an instance of a given class
30+ * in terms of the methods in the class's public API. Instead
31+ * of associating the responsibility of persistence with
32+ * the class itself as is done, for example, by the
33+ * <code>readObject</code> and <code>writeObject</code>
34+ * methods used by the <code>ObjectOutputStream</code>, streams like
35+ * the <code>XMLEncoder</code> which
36+ * use this delegation model can have their behavior controlled
37+ * independently of the classes themselves. Normally, the class
38+ * is the best place to put such information and conventions
39+ * can easily be expressed in this delegation scheme to do just that.
40+ * Sometimes however, it is the case that a minor problem
41+ * in a single class prevents an entire object graph from
42+ * being written and this can leave the application
43+ * developer with no recourse but to attempt to shadow
44+ * the problematic classes locally or use alternative
45+ * persistence techniques. In situations like these, the
46+ * delegation model gives a relatively clean mechanism for
47+ * the application developer to intervene in all parts of the
48+ * serialization process without requiring that modifications
49+ * be made to the implementation of classes which are not part
50+ * of the application itself.
51+ * <p>
52+ * In addition to using a delegation model, this persistence
53+ * scheme differs from traditional serialization schemes
54+ * in requiring an analog of the <code>writeObject</code>
55+ * method without a corresponding <code>readObject</code>
56+ * method. The <code>writeObject</code> analog encodes each
57+ * instance in terms of its public API and there is no need to
58+ * define a <code>readObject</code> analog
59+ * since the procedure for reading the serialized form
60+ * is defined by the semantics of method invocation as laid
61+ * out in the Java Language Specification.
62+ * Breaking the dependency between <code>writeObject</code>
63+ * and <code>readObject</code> implementations, which may
64+ * change from version to version, is the key factor
65+ * in making the archives produced by this technique immune
66+ * to changes in the private implementations of the classes
67+ * to which they refer.
68+ * <p>
69+ * A persistence delegate, may take control of all
70+ * aspects of the persistence of an object including:
71+ * <ul>
72+ * <li>
73+ * Deciding whether or not an instance can be mutated
74+ * into another instance of the same class.
75+ * <li>
76+ * Instantiating the object, either by calling a
77+ * public constructor or a public factory method.
78+ * <li>
79+ * Performing the initialization of the object.
80+ * </ul>
81+ * @see XMLEncoder
82+ *
83+ * @since 1.4
84+ *
85+ * @author Philip Milne
86+ */
87+
88+public abstract class PersistenceDelegate {
89+
90+ /**
91+ * The <code>writeObject</code> is a single entry point to the persistence
92+ * and is used by a <code>Encoder</code> in the traditional
93+ * mode of delegation. Although this method is not final,
94+ * it should not need to be subclassed under normal circumstances.
95+ * <p>
96+ * This implementation first checks to see if the stream
97+ * has already encountered this object. Next the
98+ * <code>mutatesTo</code> method is called to see if
99+ * that candidate returned from the stream can
100+ * be mutated into an accurate copy of <code>oldInstance</code>.
101+ * If it can, the <code>initialize</code> method is called to
102+ * perform the initialization. If not, the candidate is removed
103+ * from the stream, and the <code>instantiate</code> method
104+ * is called to create a new candidate for this object.
105+ *
106+ * @param oldInstance The instance that will be created by this expression.
107+ * @param out The stream to which this expression will be written.
108+ *
109+ * @throws NullPointerException if {@code out} is {@code null}
110+ */
111+ public void writeObject(Object oldInstance, Encoder out) {
112+ Object newInstance = out.get(oldInstance);
113+ if (!mutatesTo(oldInstance, newInstance)) {
114+ out.remove(oldInstance);
115+ out.writeExpression(instantiate(oldInstance, out));
116+ }
117+ else {
118+ initialize(oldInstance.getClass(), oldInstance, newInstance, out);
119+ }
120+ }
121+
122+ /**
123+ * Returns true if an <em>equivalent</em> copy of <code>oldInstance</code> may be
124+ * created by applying a series of statements to <code>newInstance</code>.
125+ * In the specification of this method, we mean by equivalent that the modified instance
126+ * is indistinguishable from <code>oldInstance</code> in the behavior
127+ * of the relevant methods in its public API. [Note: we use the
128+ * phrase <em>relevant</em> methods rather than <em>all</em> methods
129+ * here only because, to be strictly correct, methods like <code>hashCode</code>
130+ * and <code>toString</code> prevent most classes from producing truly
131+ * indistinguishable copies of their instances].
132+ * <p>
133+ * The default behavior returns <code>true</code>
134+ * if the classes of the two instances are the same.
135+ *
136+ * @param oldInstance The instance to be copied.
137+ * @param newInstance The instance that is to be modified.
138+ * @return True if an equivalent copy of <code>newInstance</code> may be
139+ * created by applying a series of mutations to <code>oldInstance</code>.
140+ */
141+ protected boolean mutatesTo(Object oldInstance, Object newInstance) {
142+ return (newInstance != null && oldInstance != null &&
143+ oldInstance.getClass() == newInstance.getClass());
144+ }
145+
146+ /**
147+ * Returns an expression whose value is <code>oldInstance</code>.
148+ * This method is used to characterize the constructor
149+ * or factory method that should be used to create the given object.
150+ * For example, the <code>instantiate</code> method of the persistence
151+ * delegate for the <code>Field</code> class could be defined as follows:
152+ * <pre>
153+ * Field f = (Field)oldInstance;
154+ * return new Expression(f, f.getDeclaringClass(), "getField", new Object[]{f.getName()});
155+ * </pre>
156+ * Note that we declare the value of the returned expression so that
157+ * the value of the expression (as returned by <code>getValue</code>)
158+ * will be identical to <code>oldInstance</code>.
159+ *
160+ * @param oldInstance The instance that will be created by this expression.
161+ * @param out The stream to which this expression will be written.
162+ * @return An expression whose value is <code>oldInstance</code>.
163+ *
164+ * @throws NullPointerException if {@code out} is {@code null}
165+ */
166+ protected abstract Expression instantiate(Object oldInstance, Encoder out);
167+
168+ /**
169+ * Produce a series of statements with side effects on <code>newInstance</code>
170+ * so that the new instance becomes <em>equivalent</em> to <code>oldInstance</code>.
171+ * In the specification of this method, we mean by equivalent that, after the method
172+ * returns, the modified instance is indistinguishable from
173+ * <code>newInstance</code> in the behavior of all methods in its
174+ * public API.
175+ * <p>
176+ * The implementation typically achieves this goal by producing a series of
177+ * "what happened" statements involving the <code>oldInstance</code>
178+ * and its publicly available state. These statements are sent
179+ * to the output stream using its <code>writeExpression</code>
180+ * method which returns an expression involving elements in
181+ * a cloned environment simulating the state of an input stream during
182+ * reading. Each statement returned will have had all instances
183+ * the old environment replaced with objects which exist in the new
184+ * one. In particular, references to the target of these statements,
185+ * which start out as references to <code>oldInstance</code> are returned
186+ * as references to the <code>newInstance</code> instead.
187+ * Executing these statements effects an incremental
188+ * alignment of the state of the two objects as a series of
189+ * modifications to the objects in the new environment.
190+ * By the time the initialize method returns it should be impossible
191+ * to tell the two instances apart by using their public APIs.
192+ * Most importantly, the sequence of steps that were used to make
193+ * these objects appear equivalent will have been recorded
194+ * by the output stream and will form the actual output when
195+ * the stream is flushed.
196+ * <p>
197+ * The default implementation, calls the <code>initialize</code>
198+ * method of the type's superclass.
199+ *
200+ * @param oldInstance The instance to be copied.
201+ * @param newInstance The instance that is to be modified.
202+ * @param out The stream to which any initialization statements should be written.
203+ *
204+ * @throws NullPointerException if {@code out} is {@code null}
205+ */
206+ protected void initialize(Class<?> type,
207+ Object oldInstance, Object newInstance,
208+ Encoder out)
209+ {
210+ Class superType = type.getSuperclass();
211+ PersistenceDelegate info = out.getPersistenceDelegate(superType);
212+ info.initialize(superType, oldInstance, newInstance, out);
213+ }
214+}