1 /*
2 * Copyright (c) 2000, 2011, 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 import com.sun.beans.finder.PersistenceDelegateFinder;
28
29 import java.util.HashMap;
30 import java.util.IdentityHashMap;
31 import java.util.Map;
32
33 /**
34 * An <code>Encoder</code> is a class which can be used to create
35 * files or streams that encode the state of a collection of
36 * JavaBeans in terms of their public APIs. The <code>Encoder</code>,
37 * in conjunction with its persistence delegates, is responsible for
38 * breaking the object graph down into a series of <code>Statements</code>s
39 * and <code>Expression</code>s which can be used to create it.
40 * A subclass typically provides a syntax for these expressions
41 * using some human readable form - like Java source code or XML.
42 *
43 * @since 1.4
44 *
45 * @author Philip Milne
46 */
47
48 public class Encoder {
49 private final PersistenceDelegateFinder finder = new PersistenceDelegateFinder();
50 private Map<Object, Expression> bindings = new IdentityHashMap<>();
51 private ExceptionListener exceptionListener;
52 boolean executeStatements = true;
53 private Map<Object, Object> 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 by applying
116 * the following rules in order:
117 * <ol>
118 * <li>
119 * If a persistence delegate is associated with the given type
120 * by using the {@link #setPersistenceDelegate} method
121 * it is returned.
122 * <li>
123 * A persistence delegate is then looked up by the name
124 * composed of the fully qualified name of the given type
125 * and the "PersistenceDelegate" postfix.
126 * For example, a persistence delegate for the {@code Bean} class
127 * should be named {@code BeanPersistenceDelegate}
128 * and located in the same package.
129 * <pre>
130 * public class Bean { ... }
131 * public class BeanPersistenceDelegate { ... }</pre>
132 * The instance of the {@code BeanPersistenceDelegate} class
133 * is returned for the {@code Bean} class.
134 * <li>
135 * If the type is {@code null},
136 * a shared internal persistence delegate is returned
137 * that encodes {@code null} value.
138 * <li>
139 * If the type is a {@code enum} declaration,
140 * a shared internal persistence delegate is returned
141 * that encodes constants of this enumeration
142 * by their names.
143 * <li>
144 * If the type is a primitive type or the corresponding wrapper,
145 * a shared internal persistence delegate is returned
146 * that encodes values of the given type.
147 * <li>
148 * If the type is an array,
149 * a shared internal persistence delegate is returned
150 * that encodes an array of the appropriate type and length,
151 * and each of its elements as if they are properties.
152 * <li>
153 * If the type is a proxy,
154 * a shared internal persistence delegate is returned
155 * that encodes a proxy instance by using
156 * the {@link java.lang.reflect.Proxy#newProxyInstance} method.
157 * <li>
158 * If the {@link BeanInfo} for this type has a {@link BeanDescriptor}
159 * which defined a "persistenceDelegate" attribute,
160 * the value of this named attribute is returned.
161 * <li>
162 * In all other cases the default persistence delegate is returned.
163 * The default persistence delegate assumes the type is a <em>JavaBean</em>,
164 * implying that it has a default constructor and that its state
165 * may be characterized by the matching pairs of "setter" and "getter"
166 * methods returned by the {@link Introspector} class.
167 * The default constructor is the constructor with the greatest number
168 * of parameters that has the {@link ConstructorProperties} annotation.
169 * If none of the constructors has the {@code ConstructorProperties} annotation,
170 * then the nullary constructor (constructor with no parameters) will be used.
171 * For example, in the following code fragment, the nullary constructor
172 * for the {@code Foo} class will be used,
173 * while the two-parameter constructor
174 * for the {@code Bar} class will be used.
175 * <pre>
176 * public class Foo {
177 * public Foo() { ... }
178 * public Foo(int x) { ... }
179 * }
180 * public class Bar {
181 * public Bar() { ... }
182 * @ConstructorProperties({"x"})
183 * public Bar(int x) { ... }
184 * @ConstructorProperties({"x", "y"})
185 * public Bar(int x, int y) { ... }
186 * }</pre>
187 * </ol>
188 *
189 * @param type the class of the objects
190 * @return the persistence delegate for the given type
191 *
192 * @see #setPersistenceDelegate
193 * @see java.beans.Introspector#getBeanInfo
194 * @see java.beans.BeanInfo#getBeanDescriptor
195 */
196 public PersistenceDelegate getPersistenceDelegate(Class<?> type) {
197 PersistenceDelegate pd = this.finder.find(type);
198 if (pd == null) {
199 pd = MetaData.getPersistenceDelegate(type);
200 if (pd != null) {
201 this.finder.register(type, pd);
202 }
203 }
204 return pd;
205 }
206
207 /**
208 * Associates the specified persistence delegate with the given type.
209 *
210 * @param type the class of objects that the specified persistence delegate applies to
211 * @param delegate the persistence delegate for instances of the given type
212 *
213 * @see #getPersistenceDelegate
214 * @see java.beans.Introspector#getBeanInfo
215 * @see java.beans.BeanInfo#getBeanDescriptor
216 */
217 public void setPersistenceDelegate(Class<?> type, PersistenceDelegate delegate) {
218 this.finder.register(type, delegate);
219 }
220
221 /**
222 * Removes the entry for this instance, returning the old entry.
223 *
224 * @param oldInstance The entry that should be removed.
225 * @return The entry that was removed.
226 *
227 * @see #get
228 */
229 public Object remove(Object oldInstance) {
230 Expression exp = bindings.remove(oldInstance);
231 return getValue(exp);
232 }
233
234 /**
235 * Returns a tentative value for <code>oldInstance</code> in
236 * the environment created by this stream. A persistence
237 * delegate can use its <code>mutatesTo</code> method to
238 * determine whether this value may be initialized to
239 * form the equivalent object at the output or whether
240 * a new object must be instantiated afresh. If the
241 * stream has not yet seen this value, null is returned.
242 *
243 * @param oldInstance The instance to be looked up.
244 * @return The object, null if the object has not been seen before.
245 */
246 public Object get(Object oldInstance) {
247 if (oldInstance == null || oldInstance == this ||
248 oldInstance.getClass() == String.class) {
249 return oldInstance;
250 }
251 Expression exp = bindings.get(oldInstance);
252 return getValue(exp);
253 }
254
255 private Object writeObject1(Object oldInstance) {
256 Object o = get(oldInstance);
257 if (o == null) {
258 writeObject(oldInstance);
259 o = get(oldInstance);
260 }
261 return o;
262 }
263
264 private Statement cloneStatement(Statement oldExp) {
265 Object oldTarget = oldExp.getTarget();
266 Object newTarget = writeObject1(oldTarget);
267
268 Object[] oldArgs = oldExp.getArguments();
269 Object[] newArgs = new Object[oldArgs.length];
270 for (int i = 0; i < oldArgs.length; i++) {
271 newArgs[i] = writeObject1(oldArgs[i]);
272 }
273 Statement newExp = Statement.class.equals(oldExp.getClass())
274 ? new Statement(newTarget, oldExp.getMethodName(), newArgs)
275 : new Expression(newTarget, oldExp.getMethodName(), newArgs);
276 newExp.loader = oldExp.loader;
277 return newExp;
278 }
279
280 /**
281 * Writes statement <code>oldStm</code> to the stream.
282 * The <code>oldStm</code> should be written entirely
283 * in terms of the callers environment, i.e. the
284 * target and all arguments should be part of the
285 * object graph being written. These expressions
286 * represent a series of "what happened" expressions
287 * which tell the output stream how to produce an
288 * object graph like the original.
289 * <p>
290 * The implementation of this method will produce
291 * a second expression to represent the same expression in
292 * an environment that will exist when the stream is read.
293 * This is achieved simply by calling <code>writeObject</code>
294 * on the target and all the arguments and building a new
295 * expression with the results.
296 *
297 * @param oldStm The expression to be written to the stream.
298 */
299 public void writeStatement(Statement oldStm) {
300 // System.out.println("writeStatement: " + oldExp);
301 Statement newStm = cloneStatement(oldStm);
302 if (oldStm.getTarget() != this && executeStatements) {
303 try {
304 newStm.execute();
305 } catch (Exception e) {
306 getExceptionListener().exceptionThrown(new Exception("Encoder: discarding statement "
307 + newStm, e));
308 }
309 }
310 }
311
312 /**
313 * The implementation first checks to see if an
314 * expression with this value has already been written.
315 * If not, the expression is cloned, using
316 * the same procedure as <code>writeStatement</code>,
317 * and the value of this expression is reconciled
318 * with the value of the cloned expression
319 * by calling <code>writeObject</code>.
320 *
321 * @param oldExp The expression to be written to the stream.
322 */
323 public void writeExpression(Expression oldExp) {
324 // System.out.println("Encoder::writeExpression: " + oldExp);
325 Object oldValue = getValue(oldExp);
326 if (get(oldValue) != null) {
327 return;
328 }
329 bindings.put(oldValue, (Expression)cloneStatement(oldExp));
330 writeObject(oldValue);
331 }
332
333 void clear() {
334 bindings.clear();
335 }
336
337 // Package private method for setting an attributes table for the encoder
338 void setAttribute(Object key, Object value) {
339 if (attributes == null) {
340 attributes = new HashMap<>();
341 }
342 attributes.put(key, value);
343 }
344
345 Object getAttribute(Object key) {
346 if (attributes == null) {
347 return null;
348 }
349 return attributes.get(key);
350 }
351 }