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/* * @(#)Encoder.java 1.22 06/02/27 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.beans; import java.io.*; import java.util.*; /** * An <code>Encoder</code> is a class which can be used to create * files or streams that encode the state of a collection of * JavaBeans in terms of their public APIs. The <code>Encoder</code>, * in conjunction with its persistence delegates, is responsible for * breaking the object graph down into a series of <code>Statements</code>s * and <code>Expression</code>s which can be used to create it. * A subclass typically provides a syntax for these expressions * using some human readable form - like Java source code or XML. * * @since 1.4 * * @version 1.3 11/15/00 * @author Philip Milne */ public class Encoder { private Map bindings = new IdentityHashMap(); private ExceptionListener exceptionListener; boolean executeStatements = true; private Map attributes; /** * Write the specified object to the output stream. * The serialized form will denote a series of * expressions, the combined effect of which will create * an equivalent object when the input stream is read. * By default, the object is assumed to be a <em>JavaBean</em> * with a nullary constructor, whose state is defined by * the matching pairs of "setter" and "getter" methods * returned by the Introspector. * * @param o The object to be written to the stream. * * @see XMLDecoder#readObject */ protected void writeObject(Object o) { if (o == this) { return; } PersistenceDelegate info = getPersistenceDelegate(o == null ? null : o.getClass()); info.writeObject(o, this); } /** * Sets the exception handler for this stream to <code>exceptionListener</code>. * The exception handler is notified when this stream catches recoverable * exceptions. * * @param exceptionListener The exception handler for this stream; * if <code>null</code> the default exception listener will be used. * * @see #getExceptionListener */ public void setExceptionListener(ExceptionListener exceptionListener) { this.exceptionListener = exceptionListener; } /** * Gets the exception handler for this stream. * * @return The exception handler for this stream; * Will return the default exception listener if this has not explicitly been set. * * @see #setExceptionListener */ public ExceptionListener getExceptionListener() { return (exceptionListener != null) ? exceptionListener : Statement.defaultExceptionListener; } Object getValue(Expression exp) { try { return (exp == null) ? null : exp.getValue(); } catch (Exception e) { getExceptionListener().exceptionThrown(e); throw new RuntimeException("failed to evaluate: " + exp.toString()); } } /** * Returns the persistence delegate for the given type. * The persistence delegate is calculated * by applying the following of rules in order: * <ul> * <li> * If the type is an array, an internal persistence * delegate is returned which will instantiate an * array of the appropriate type and length, initializing * each of its elements as if they are properties. * <li> * If the type is a proxy, an internal persistence * delegate is returned which will instantiate a * new proxy instance using the static * "newProxyInstance" method defined in the * Proxy class. * <li> * If the BeanInfo for this type has a <code>BeanDescriptor</code> * which defined a "persistenceDelegate" property, this * value is returned. * <li> * In all other cases the default persistence delegate * is returned. The default persistence delegate assumes * the type is a <em>JavaBean</em>, implying that it has a default constructor * and that its state may be characterized by the matching pairs * of "setter" and "getter" methods returned by the Introspector. * The default constructor is the constructor with the greatest number * of parameters that has the {@link ConstructorProperties} annotation. * If none of the constructors have the {@code ConstructorProperties} annotation, * then the nullary constructor (constructor with no parameters) will be used. * For example, in the following the nullary constructor * for {@code Foo} will be used, while the two parameter constructor * for {@code Bar} will be used. * <code> * public class Foo { * public Foo() { ... } * public Foo(int x) { ... } * } * public class Bar { * public Bar() { ... } * @ConstructorProperties({"x"}) * public Bar(int x) { ... } * @ConstructorProperties({"x", "y"}) * public Bar(int x, int y) { ... } * } * </code> * </ul> * * @param type The type of the object. * @return The persistence delegate for this type of object. * * @see #setPersistenceDelegate * @see java.beans.Introspector#getBeanInfo * @see java.beans.BeanInfo#getBeanDescriptor */ public PersistenceDelegate getPersistenceDelegate(Class<?> type) { return MetaData.getPersistenceDelegate(type); } /** * Sets the persistence delegate associated with this <code>type</code> to * <code>persistenceDelegate</code>. * * @param type The class of objects that <code>persistenceDelegate</code> applies to. * @param persistenceDelegate The persistence delegate for instances of <code>type</code>. * * @see #getPersistenceDelegate * @see java.beans.Introspector#getBeanInfo * @see java.beans.BeanInfo#getBeanDescriptor */ public void setPersistenceDelegate(Class<?> type, PersistenceDelegate persistenceDelegate) { MetaData.setPersistenceDelegate(type, persistenceDelegate); } /** * Removes the entry for this instance, returning the old entry. * * @param oldInstance The entry that should be removed. * @return The entry that was removed. * * @see #get */ public Object remove(Object oldInstance) { Expression exp = (Expression)bindings.remove(oldInstance); return getValue(exp); } /** * Returns a tentative value for <code>oldInstance</code> in * the environment created by this stream. A persistence * delegate can use its <code>mutatesTo</code> method to * determine whether this value may be initialized to * form the equivalent object at the output or whether * a new object must be instantiated afresh. If the * stream has not yet seen this value, null is returned. * * @param oldInstance The instance to be looked up. * @return The object, null if the object has not been seen before. */ public Object get(Object oldInstance) { if (oldInstance == null || oldInstance == this || oldInstance.getClass() == String.class) { return oldInstance; } Expression exp = (Expression)bindings.get(oldInstance); return getValue(exp); } private Object writeObject1(Object oldInstance) { Object o = get(oldInstance); if (o == null) { writeObject(oldInstance); o = get(oldInstance); } return o; } private Statement cloneStatement(Statement oldExp) { Object oldTarget = oldExp.getTarget(); Object newTarget = writeObject1(oldTarget); Object[] oldArgs = oldExp.getArguments(); Object[] newArgs = new Object[oldArgs.length]; for (int i = 0; i < oldArgs.length; i++) { newArgs[i] = writeObject1(oldArgs[i]); } if (oldExp.getClass() == Statement.class) { return new Statement(newTarget, oldExp.getMethodName(), newArgs); } else { return new Expression(newTarget, oldExp.getMethodName(), newArgs); } } /** * Writes statement <code>oldStm</code> to the stream. * The <code>oldStm</code> should be written entirely * in terms of the callers environment, i.e. the * target and all arguments should be part of the * object graph being written. These expressions * represent a series of "what happened" expressions * which tell the output stream how to produce an * object graph like the original. * <p> * The implementation of this method will produce * a second expression to represent the same expression in * an environment that will exist when the stream is read. * This is achieved simply by calling <code>writeObject</code> * on the target and all the arguments and building a new * expression with the results. * * @param oldStm The expression to be written to the stream. */ public void writeStatement(Statement oldStm) { // System.out.println("writeStatement: " + oldExp); Statement newStm = cloneStatement(oldStm); if (oldStm.getTarget() != this && executeStatements) { try { newStm.execute(); } catch (Exception e) { getExceptionListener().exceptionThrown(new Exception("Encoder: discarding statement " + newStm, e)); } } } /** * The implementation first checks to see if an * expression with this value has already been written. * If not, the expression is cloned, using * the same procedure as <code>writeStatement</code>, * and the value of this expression is reconciled * with the value of the cloned expression * by calling <code>writeObject</code>. * * @param oldExp The expression to be written to the stream. */ public void writeExpression(Expression oldExp) { // System.out.println("Encoder::writeExpression: " + oldExp); Object oldValue = getValue(oldExp); if (get(oldValue) != null) { return; } bindings.put(oldValue, (Expression)cloneStatement(oldExp)); writeObject(oldValue); } void clear() { bindings.clear(); } // Package private method for setting an attributes table for the encoder void setAttribute(Object key, Object value) { if (attributes == null) { attributes = new HashMap(); } attributes.put(key, value); } Object getAttribute(Object key) { if (attributes == null) { return null; } return attributes.get(key); } }