1 /*
2 * Copyright 2000-2007 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any questions.
24 */
25 package java.beans;
26
27 import java.util.Collections;
28 import java.util.HashMap;
29 import java.util.IdentityHashMap;
30 import java.util.Map;
31
32 /**
33 * An <code>Encoder</code> is a class which can be used to create
34 * files or streams that encode the state of a collection of
35 * JavaBeans in terms of their public APIs. The <code>Encoder</code>,
36 * in conjunction with its persistence delegates, is responsible for
37 * breaking the object graph down into a series of <code>Statements</code>s
38 * and <code>Expression</code>s which can be used to create it.
39 * A subclass typically provides a syntax for these expressions
40 * using some human readable form - like Java source code or XML.
41 *
42 * @since 1.4
43 *
44 * @author Philip Milne
45 */
46
47 public class Encoder {
48 private final Map<Class<?>, PersistenceDelegate> delegates
49 = Collections.synchronizedMap(new HashMap<Class<?>, PersistenceDelegate>());
50 private Map bindings = new IdentityHashMap();
51 private ExceptionListener exceptionListener;
52 boolean executeStatements = true;
53 private Map attributes;
54
55 /**
56 * Write the specified object to the output stream.
57 * The serialized form will denote a series of
58 * expressions, the combined effect of which will create
59 * an equivalent object when the input stream is read.
60 * By default, the object is assumed to be a <em>JavaBean</em>
61 * with a nullary constructor, whose state is defined by
62 * the matching pairs of "setter" and "getter" methods
63 * returned by the Introspector.
64 *
65 * @param o The object to be written to the stream.
66 *
67 * @see XMLDecoder#readObject
68 */
69 protected void writeObject(Object o) {
70 if (o == this) {
71 return;
72 }
73 PersistenceDelegate info = getPersistenceDelegate(o == null ? null : o.getClass());
74 info.writeObject(o, this);
75 }
76
77 /**
78 * Sets the exception handler for this stream to <code>exceptionListener</code>.
79 * The exception handler is notified when this stream catches recoverable
80 * exceptions.
81 *
82 * @param exceptionListener The exception handler for this stream;
83 * if <code>null</code> the default exception listener will be used.
84 *
85 * @see #getExceptionListener
86 */
87 public void setExceptionListener(ExceptionListener exceptionListener) {
88 this.exceptionListener = exceptionListener;
89 }
90
91 /**
92 * Gets the exception handler for this stream.
93 *
94 * @return The exception handler for this stream;
95 * Will return the default exception listener if this has not explicitly been set.
96 *
97 * @see #setExceptionListener
98 */
99 public ExceptionListener getExceptionListener() {
100 return (exceptionListener != null) ? exceptionListener : Statement.defaultExceptionListener;
101 }
102
103 Object getValue(Expression exp) {
104 try {
105 return (exp == null) ? null : exp.getValue();
106 }
107 catch (Exception e) {
108 getExceptionListener().exceptionThrown(e);
109 throw new RuntimeException("failed to evaluate: " + exp.toString());
110 }
111 }
112
113 /**
114 * Returns the persistence delegate for the given type.
115 * The persistence delegate is calculated
116 * by applying the following of rules in order:
117 * <ul>
118 * <li>
119 * If the type is an array, an internal persistence
120 * delegate is returned which will instantiate an
121 * array of the appropriate type and length, initializing
122 * each of its elements as if they are properties.
123 * <li>
124 * If the type is a proxy, an internal persistence
125 * delegate is returned which will instantiate a
126 * new proxy instance using the static
127 * "newProxyInstance" method defined in the
128 * Proxy class.
129 * <li>
130 * If the BeanInfo for this type has a <code>BeanDescriptor</code>
131 * which defined a "persistenceDelegate" property, this
132 * value is returned.
133 * <li>
134 * In all other cases the default persistence delegate
135 * is returned. The default persistence delegate assumes
136 * the type is a <em>JavaBean</em>, implying that it has a default constructor
137 * and that its state may be characterized by the matching pairs
138 * of "setter" and "getter" methods returned by the Introspector.
139 * The default constructor is the constructor with the greatest number
140 * of parameters that has the {@link ConstructorProperties} annotation.
141 * If none of the constructors have the {@code ConstructorProperties} annotation,
142 * then the nullary constructor (constructor with no parameters) will be used.
143 * For example, in the following the nullary constructor
144 * for {@code Foo} will be used, while the two parameter constructor
145 * for {@code Bar} will be used.
146 * <code>
147 * public class Foo {
148 * public Foo() { ... }
149 * public Foo(int x) { ... }
150 * }
151 * public class Bar {
152 * public Bar() { ... }
153 * @ConstructorProperties({"x"})
154 * public Bar(int x) { ... }
155 * @ConstructorProperties({"x", "y"})
156 * public Bar(int x, int y) { ... }
157 * }
158 * </code>
159 * </ul>
160 *
161 * @param type The type of the object.
162 * @return The persistence delegate for this type of object.
163 *
164 * @see #setPersistenceDelegate
165 * @see java.beans.Introspector#getBeanInfo
166 * @see java.beans.BeanInfo#getBeanDescriptor
167 */
168 public PersistenceDelegate getPersistenceDelegate(Class<?> type) {
169 PersistenceDelegate pd = this.delegates.get(type);
170 return (pd != null) ? pd : MetaData.getPersistenceDelegate(type);
171 }
172
173 /**
174 * Sets the persistence delegate associated with this <code>type</code> to
175 * <code>persistenceDelegate</code>.
176 *
177 * @param type The class of objects that <code>persistenceDelegate</code> applies to.
178 * @param persistenceDelegate The persistence delegate for instances of <code>type</code>.
179 *
180 * @see #getPersistenceDelegate
181 * @see java.beans.Introspector#getBeanInfo
182 * @see java.beans.BeanInfo#getBeanDescriptor
183 */
184 public void setPersistenceDelegate(Class<?> type,
185 PersistenceDelegate persistenceDelegate)
186 {
187 if (persistenceDelegate != null) {
188 this.delegates.put(type, persistenceDelegate);
189 } else {
190 this.delegates.remove(type);
191 }
192 }
193
194 /**
195 * Removes the entry for this instance, returning the old entry.
196 *
197 * @param oldInstance The entry that should be removed.
198 * @return The entry that was removed.
199 *
200 * @see #get
201 */
202 public Object remove(Object oldInstance) {
203 Expression exp = (Expression)bindings.remove(oldInstance);
204 return getValue(exp);
205 }
206
207 /**
208 * Returns a tentative value for <code>oldInstance</code> in
209 * the environment created by this stream. A persistence
210 * delegate can use its <code>mutatesTo</code> method to
211 * determine whether this value may be initialized to
212 * form the equivalent object at the output or whether
213 * a new object must be instantiated afresh. If the
214 * stream has not yet seen this value, null is returned.
215 *
216 * @param oldInstance The instance to be looked up.
217 * @return The object, null if the object has not been seen before.
218 */
219 public Object get(Object oldInstance) {
220 if (oldInstance == null || oldInstance == this ||
221 oldInstance.getClass() == String.class) {
222 return oldInstance;
223 }
224 Expression exp = (Expression)bindings.get(oldInstance);
225 return getValue(exp);
226 }
227
228 private Object writeObject1(Object oldInstance) {
229 Object o = get(oldInstance);
230 if (o == null) {
231 writeObject(oldInstance);
232 o = get(oldInstance);
233 }
234 return o;
235 }
236
237 private Statement cloneStatement(Statement oldExp) {
238 Object oldTarget = oldExp.getTarget();
239 Object newTarget = writeObject1(oldTarget);
240
241 Object[] oldArgs = oldExp.getArguments();
242 Object[] newArgs = new Object[oldArgs.length];
243 for (int i = 0; i < oldArgs.length; i++) {
244 newArgs[i] = writeObject1(oldArgs[i]);
245 }
246 if (oldExp.getClass() == Statement.class) {
247 return new Statement(newTarget, oldExp.getMethodName(), newArgs);
248 }
249 else {
250 return new Expression(newTarget, oldExp.getMethodName(), newArgs);
251 }
252 }
253
254 /**
255 * Writes statement <code>oldStm</code> to the stream.
256 * The <code>oldStm</code> should be written entirely
257 * in terms of the callers environment, i.e. the
258 * target and all arguments should be part of the
259 * object graph being written. These expressions
260 * represent a series of "what happened" expressions
261 * which tell the output stream how to produce an
262 * object graph like the original.
263 * <p>
264 * The implementation of this method will produce
265 * a second expression to represent the same expression in
266 * an environment that will exist when the stream is read.
267 * This is achieved simply by calling <code>writeObject</code>
268 * on the target and all the arguments and building a new
269 * expression with the results.
270 *
271 * @param oldStm The expression to be written to the stream.
272 */
273 public void writeStatement(Statement oldStm) {
274 // System.out.println("writeStatement: " + oldExp);
275 Statement newStm = cloneStatement(oldStm);
276 if (oldStm.getTarget() != this && executeStatements) {
277 try {
278 newStm.execute();
279 } catch (Exception e) {
280 getExceptionListener().exceptionThrown(new Exception("Encoder: discarding statement "
281 + newStm, e));
282 }
283 }
284 }
285
286 /**
287 * The implementation first checks to see if an
288 * expression with this value has already been written.
289 * If not, the expression is cloned, using
290 * the same procedure as <code>writeStatement</code>,
291 * and the value of this expression is reconciled
292 * with the value of the cloned expression
293 * by calling <code>writeObject</code>.
294 *
295 * @param oldExp The expression to be written to the stream.
296 */
297 public void writeExpression(Expression oldExp) {
298 // System.out.println("Encoder::writeExpression: " + oldExp);
299 Object oldValue = getValue(oldExp);
300 if (get(oldValue) != null) {
301 return;
302 }
303 bindings.put(oldValue, (Expression)cloneStatement(oldExp));
304 writeObject(oldValue);
305 }
306
307 void clear() {
308 bindings.clear();
309 }
310
311 // Package private method for setting an attributes table for the encoder
312 void setAttribute(Object key, Object value) {
313 if (attributes == null) {
314 attributes = new HashMap();
315 }
316 attributes.put(key, value);
317 }
318
319 Object getAttribute(Object key) {
320 if (attributes == null) {
321 return null;
322 }
323 return attributes.get(key);
324 }
325 }
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