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* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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*/
package java.beans;
import com.sun.beans.finder.
PersistenceDelegateFinder;
import java.util.
HashMap;
import java.util.
IdentityHashMap;
import java.util.
Map;
/**
* 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
*
* @author Philip Milne
*/
public class
Encoder {
private final
PersistenceDelegateFinder finder = new
PersistenceDelegateFinder();
private
Map<
Object,
Expression>
bindings = new
IdentityHashMap<>();
private
ExceptionListener exceptionListener;
boolean
executeStatements = true;
private
Map<
Object,
Object>
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 rules in order:
* <ol>
* <li>
* If a persistence delegate is associated with the given type
* by using the {@link #setPersistenceDelegate} method
* it is returned.
* <li>
* A persistence delegate is then looked up by the name
* composed of the the fully qualified name of the given type
* and the "PersistenceDelegate" postfix.
* For example, a persistence delegate for the {@code Bean} class
* should be named {@code BeanPersistenceDelegate}
* and located in the same package.
* <pre>
* public class Bean { ... }
* public class BeanPersistenceDelegate { ... }</pre>
* The instance of the {@code BeanPersistenceDelegate} class
* is returned for the {@code Bean} class.
* <li>
* If the type is {@code null},
* a shared internal persistence delegate is returned
* that encodes {@code null} value.
* <li>
* If the type is a {@code enum} declaration,
* a shared internal persistence delegate is returned
* that encodes constants of this enumeration
* by their names.
* <li>
* If the type is a primitive type or the corresponding wrapper,
* a shared internal persistence delegate is returned
* that encodes values of the given type.
* <li>
* If the type is an array,
* a shared internal persistence delegate is returned
* that encodes an array of the appropriate type and length,
* and each of its elements as if they are properties.
* <li>
* If the type is a proxy,
* a shared internal persistence delegate is returned
* that encodes a proxy instance by using
* the {@link java.lang.reflect.Proxy#newProxyInstance} method.
* <li>
* If the {@link BeanInfo} for this type has a {@link BeanDescriptor}
* which defined a "persistenceDelegate" attribute,
* the value of this named attribute 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 {@link Introspector} class.
* The default constructor is the constructor with the greatest number
* of parameters that has the {@link ConstructorProperties} annotation.
* If none of the constructors has the {@code ConstructorProperties} annotation,
* then the nullary constructor (constructor with no parameters) will be used.
* For example, in the following code fragment, the nullary constructor
* for the {@code Foo} class will be used,
* while the two-parameter constructor
* for the {@code Bar} class will be used.
* <pre>
* 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) { ... }
* }</pre>
* </ol>
*
* @param type the class of the objects
* @return the persistence delegate for the given type
*
* @see #setPersistenceDelegate
* @see java.beans.Introspector#getBeanInfo
* @see java.beans.BeanInfo#getBeanDescriptor
*/
public
PersistenceDelegate getPersistenceDelegate(
Class<?>
type) {
PersistenceDelegate pd = this.
finder.
find(
type);
if (
pd == null) {
pd =
MetaData.
getPersistenceDelegate(
type);
if (
pd != null) {
this.
finder.
register(
type,
pd);
}
}
return
pd;
}
/**
* Associates the specified persistence delegate with the given type.
*
* @param type the class of objects that the specified persistence delegate applies to
* @param delegate the persistence delegate for instances of the given type
*
* @see #getPersistenceDelegate
* @see java.beans.Introspector#getBeanInfo
* @see java.beans.BeanInfo#getBeanDescriptor
*/
public void
setPersistenceDelegate(
Class<?>
type,
PersistenceDelegate delegate) {
this.
finder.
register(
type,
delegate);
}
/**
* 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 =
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 =
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]);
}
Statement newExp =
Statement.class.
equals(
oldExp.
getClass())
? new
Statement(
newTarget,
oldExp.
getMethodName(),
newArgs)
: new
Expression(
newTarget,
oldExp.
getMethodName(),
newArgs);
newExp.
loader =
oldExp.
loader;
return
newExp;
}
/**
* 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);
}
}