/*
* @(#)XMLEncoder.java 1.35 06/03/09
*
* 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.*;
import java.lang.reflect.*;
import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.UnsupportedCharsetException;
/**
* The <code>XMLEncoder</code> class is a complementary alternative to
* the <code>ObjectOutputStream</code> and can used to generate
* a textual representation of a <em>JavaBean</em> in the same
* way that the <code>ObjectOutputStream</code> can
* be used to create binary representation of <code>Serializable</code>
* objects. For example, the following fragment can be used to create
* a textual representation the supplied <em>JavaBean</em>
* and all its properties:
* <pre>
* XMLEncoder e = new XMLEncoder(
* new BufferedOutputStream(
* new FileOutputStream("Test.xml")));
* e.writeObject(new JButton("Hello, world"));
* e.close();
* </pre>
* Despite the similarity of their APIs, the <code>XMLEncoder</code>
* class is exclusively designed for the purpose of archiving graphs
* of <em>JavaBean</em>s as textual representations of their public
* properties. Like Java source files, documents written this way
* have a natural immunity to changes in the implementations of the classes
* involved. The <code>ObjectOutputStream</code> continues to be recommended
* for interprocess communication and general purpose serialization.
* <p>
* The <code>XMLEncoder</code> class provides a default denotation for
* <em>JavaBean</em>s in which they are represented as XML documents
* complying with version 1.0 of the XML specification and the
* UTF-8 character encoding of the Unicode/ISO 10646 character set.
* The XML documents produced by the <code>XMLEncoder</code> class are:
* <ul>
* <li>
* <em>Portable and version resilient</em>: they have no dependencies
* on the private implementation of any class and so, like Java source
* files, they may be exchanged between environments which may have
* different versions of some of the classes and between VMs from
* different vendors.
* <li>
* <em>Structurally compact</em>: The <code>XMLEncoder</code> class
* uses a <em>redundancy elimination</em> algorithm internally so that the
* default values of a Bean's properties are not written to the stream.
* <li>
* <em>Fault tolerant</em>: Non-structural errors in the file,
* caused either by damage to the file or by API changes
* made to classes in an archive remain localized
* so that a reader can report the error and continue to load the parts
* of the document which were not affected by the error.
* </ul>
* <p>
* Below is an example of an XML archive containing
* some user interface components from the <em>swing</em> toolkit:
* <pre>
* <?xml version="1.0" encoding="UTF-8"?>
* <java version="1.0" class="java.beans.XMLDecoder">
* <object class="javax.swing.JFrame">
* <void property="name">
* <string>frame1</string>
* </void>
* <void property="bounds">
* <object class="java.awt.Rectangle">
* <int>0</int>
* <int>0</int>
* <int>200</int>
* <int>200</int>
* </object>
* </void>
* <void property="contentPane">
* <void method="add">
* <object class="javax.swing.JButton">
* <void property="label">
* <string>Hello</string>
* </void>
* </object>
* </void>
* </void>
* <void property="visible">
* <boolean>true</boolean>
* </void>
* </object>
* </java>
* </pre>
* The XML syntax uses the following conventions:
* <ul>
* <li>
* Each element represents a method call.
* <li>
* The "object" tag denotes an <em>expression</em> whose value is
* to be used as the argument to the enclosing element.
* <li>
* The "void" tag denotes a <em>statement</em> which will
* be executed, but whose result will not be used as an
* argument to the enclosing method.
* <li>
* Elements which contain elements use those elements as arguments,
* unless they have the tag: "void".
* <li>
* The name of the method is denoted by the "method" attribute.
* <li>
* XML's standard "id" and "idref" attributes are used to make
* references to previous expressions - so as to deal with
* circularities in the object graph.
* <li>
* The "class" attribute is used to specify the target of a static
* method or constructor explicitly; its value being the fully
* qualified name of the class.
* <li>
* Elements with the "void" tag are executed using
* the outer context as the target if no target is defined
* by a "class" attribute.
* <li>
* Java's String class is treated specially and is
* written <string>Hello, world</string> where
* the characters of the string are converted to bytes
* using the UTF-8 character encoding.
* </ul>
* <p>
* Although all object graphs may be written using just these three
* tags, the following definitions are included so that common
* data structures can be expressed more concisely:
* <p>
* <ul>
* <li>
* The default method name is "new".
* <li>
* A reference to a java class is written in the form
* <class>javax.swing.JButton</class>.
* <li>
* Instances of the wrapper classes for Java's primitive types are written
* using the name of the primitive type as the tag. For example, an
* instance of the <code>Integer</code> class could be written:
* <int>123</int>. Note that the <code>XMLEncoder</code> class
* uses Java's reflection package in which the conversion between
* Java's primitive types and their associated "wrapper classes"
* is handled internally. The API for the <code>XMLEncoder</code> class
* itself deals only with <code>Object</code>s.
* <li>
* In an element representing a nullary method whose name
* starts with "get", the "method" attribute is replaced
* with a "property" attribute whose value is given by removing
* the "get" prefix and decapitalizing the result.
* <li>
* In an element representing a monadic method whose name
* starts with "set", the "method" attribute is replaced
* with a "property" attribute whose value is given by removing
* the "set" prefix and decapitalizing the result.
* <li>
* In an element representing a method named "get" taking one
* integer argument, the "method" attribute is replaced
* with an "index" attribute whose value the value of the
* first argument.
* <li>
* In an element representing a method named "set" taking two arguments,
* the first of which is an integer, the "method" attribute is replaced
* with an "index" attribute whose value the value of the
* first argument.
* <li>
* A reference to an array is written using the "array"
* tag. The "class" and "length" attributes specify the
* sub-type of the array and its length respectively.
* </ul>
*
*<p>
* For more information you might also want to check out
* <a
href="http://java.sun.com/products/jfc/tsc/articles/persistence4">Using XMLEncoder</a>,
* an article in <em>The Swing Connection.</em>
* @see XMLDecoder
* @see java.io.ObjectOutputStream
*
* @since 1.4
*
* @version 1.35 03/09/06
* @author Philip Milne
*/
public class XMLEncoder extends Encoder {
private static String encoding = "UTF-8";
private OutputStream out;
private Object owner;
private int indentation = 0;
private boolean internal = false;
private Map valueToExpression;
private Map targetToStatementList;
private boolean preambleWritten = false;
private NameGenerator nameGenerator;
private class ValueData {
public int refs = 0;
public boolean marked = false; // Marked -> refs > 0 unless ref was a target.
public String name = null;
public Expression exp = null;
}
/**
* Creates a new output stream for sending <em>JavaBeans</em>
* to the stream <code>out</code> using an XML encoding.
*
* @param out The stream to which the XML representation of
* the objects will be sent.
*
* @see XMLDecoder#XMLDecoder(InputStream)
*/
public XMLEncoder(OutputStream out) {
this.out = out;
valueToExpression = new IdentityHashMap();
targetToStatementList = new IdentityHashMap();
nameGenerator = new NameGenerator();
}
/**
* Sets the owner of this encoder to <code>owner</code>.
*
* @param owner The owner of this encoder.
*
* @see #getOwner
*/
public void setOwner(Object owner) {
this.owner = owner;
writeExpression(new Expression(this, "getOwner", new Object[0]));
}
/**
* Gets the owner of this encoder.
*
* @return The owner of this encoder.
*
* @see #setOwner
*/
public Object getOwner() {
return owner;
}
/**
* Write an XML representation of the specified object to the output.
*
* @param o The object to be written to the stream.
*
* @see XMLDecoder#readObject
*/
public void writeObject(Object o) {
if (internal) {
super.writeObject(o);
}
else {
writeStatement(new Statement(this, "writeObject", new Object[]{o}));
}
}
private Vector statementList(Object target) {
Vector list = (Vector)targetToStatementList.get(target);
if (list != null) {
return list;
}
list = new Vector();
targetToStatementList.put(target, list);
return list;
}
private void mark(Object o, boolean isArgument) {
if (o == null || o == this) {
return;
}
ValueData d = getValueData(o);
Expression exp = d.exp;
// Do not mark liternal strings. Other strings, which might,
// for example, come from resource bundles should still be marked.
if (o.getClass() == String.class && exp == null) {
return;
}
// Bump the reference counts of all arguments
if (isArgument) {
d.refs++;
}
if (d.marked) {
return;
}
d.marked = true;
Object target = exp.getTarget();
if (!(target instanceof Class)) {
statementList(target).add(exp);
// Pending: Why does the reference count need to
// be incremented here?
d.refs++;
}
mark(exp);
}
private void mark(Statement stm) {
Object[] args = stm.getArguments();
for (int i = 0; i < args.length; i++) {
Object arg = args[i];
mark(arg, true);
}
mark(stm.getTarget(), false);
}
/**
* Records the Statement so that the Encoder will
* produce the actual output when the stream is flushed.
* <P>
* This method should only be invoked within the context
* of initializing a persistence delegate.
*
* @param oldStm The statement that will be written
* to the stream.
* @see java.beans.PersistenceDelegate#initialize
*/
public void writeStatement(Statement oldStm) {
// System.out.println("XMLEncoder::writeStatement: " + oldStm);
boolean internal = this.internal;
this.internal = true;
try {
super.writeStatement(oldStm);
/*
Note we must do the mark first as we may
require the results of previous values in
this context for this statement.
Test case is:
os.setOwner(this);
os.writeObject(this);
*/
mark(oldStm);
statementList(oldStm.getTarget()).add(oldStm);
}
catch (Exception e) {
getExceptionListener().exceptionThrown(new Exception("XMLEncoder: discarding statement " + oldStm, e));
}
this.internal = internal;
}
/**
* Records the Expression so that the Encoder will
* produce the actual output when the stream is flushed.
* <P>
* This method should only be invoked within the context of
* initializing a persistence delegate or setting up an encoder to
* read from a resource bundle.
* <P>
* For more information about using resource bundles with the
* XMLEncoder, see
* http://java.sun.com/products/jfc/tsc/articles/persistence4/#i18n
*
* @param oldExp The expression that will be written
* to the stream.
* @see java.beans.PersistenceDelegate#initialize
*/
public void writeExpression(Expression oldExp) {
boolean internal = this.internal;
this.internal = true;
Object oldValue = getValue(oldExp);
if (get(oldValue) == null || (oldValue instanceof String && !internal)) {
getValueData(oldValue).exp = oldExp;
super.writeExpression(oldExp);
}
this.internal = internal;
}
/**
* This method writes out the preamble associated with the
* XML encoding if it has not been written already and
* then writes out all of the values that been
* written to the stream since the last time <code>flush</code>
* was called. After flushing, all internal references to the
* values that were written to this stream are cleared.
*/
public void flush() {
if (!preambleWritten) { // Don't do this in constructor - it throws ... pending.
writeln("<?xml version=" + quote("1.0") +
" encoding=" + quote(encoding) + "?>");
writeln("<java version=" + quote(System.getProperty("java.version")) +
" class=" + quote(XMLDecoder.class.getName()) + ">");
preambleWritten = true;
}
indentation++;
Vector roots = statementList(this);
for(int i = 0; i < roots.size(); i++) {
Statement s = (Statement)roots.get(i);
if ("writeObject".equals(s.getMethodName())) {
outputValue(s.getArguments()[0], this, true);
}
else {
outputStatement(s, this, false);
}
}
indentation--;
try {
out.flush();
}
catch (IOException e) {
getExceptionListener().exceptionThrown(e);
}
clear();
}
void clear() {
super.clear();
nameGenerator.clear();
valueToExpression.clear();
targetToStatementList.clear();
}
/**
* This method calls <code>flush</code>, writes the closing
* postamble and then closes the output stream associated
* with this stream.
*/
public void close() {
flush();
writeln("</java>");
try {
out.close();
}
catch (IOException e) {
getExceptionListener().exceptionThrown(e);
}
}
private String quote(String s) {
return "\"" + s + "\"";
}
private ValueData getValueData(Object o) {
ValueData d = (ValueData)valueToExpression.get(o);
if (d == null) {
d = new ValueData();
valueToExpression.put(o, d);
}
return d;
}
/**
* Returns <code>true</code> if the argument,
* a Unicode code point, is valid in XML documents.
* Unicode characters fit into the low sixteen bits of a Unicode code point,
* and pairs of Unicode <em>surrogate characters</em> can be combined
* to encode Unicode code point in documents containing only Unicode.
* (The <code>char</code> datatype in the Java Programming Language
* represents Unicode characters, including unpaired surrogates.)
* <par>
* [2] Char ::= #x0009 | #x000A | #x000D
* | [#x0020-#xD7FF]
* | [#xE000-#xFFFD]
* | [#x10000-#x10ffff]
* </par>
*
* @param code the 32-bit Unicode code point being tested
* @return <code>true</code> if the Unicode code point is valid,
* <code>false</code> otherwise
*/
private static boolean isValidCharCode(int code) {
return (0x0020 <= code && code <= 0xD7FF)
|| (0x000A == code)
|| (0x0009 == code)
|| (0x000D == code)
|| (0xE000 <= code && code <= 0xFFFD)
|| (0x10000 <= code && code <= 0x10ffff);
}
private void writeln(String exp) {
try {
for(int i = 0; i < indentation; i++) {
out.write(' ');
}
out.write(exp.getBytes(encoding));
out.write(" \n".getBytes(encoding));
}
catch (IOException e) {
getExceptionListener().exceptionThrown(e);
}
}
private void outputValue(Object value, Object outer, boolean isArgument) {
if (value == null) {
writeln("<null/>");
return;
}
if (value instanceof Class) {
writeln("<class>" + ((Class)value).getName() + "</class>");
return;
}
ValueData d = getValueData(value);
if (d.exp != null) {
Object target = d.exp.getTarget();
String methodName = d.exp.getMethodName();
if (target == null || methodName == null) {
throw new NullPointerException((target == null ? "target" :
"methodName") + " should not be null");
}
if (target instanceof Field && methodName.equals("get")) {
Field f = (Field)target;
writeln("<object class=" + quote(f.getDeclaringClass().getName()) +
" field=" + quote(f.getName()) + "/>");
return;
}
Class primitiveType = ReflectionUtils.primitiveTypeFor(value.getClass());
if (primitiveType != null && target == value.getClass() &&
methodName.equals("new")) {
String primitiveTypeName = primitiveType.getName();
// Make sure that character types are quoted correctly.
if (primitiveType == Character.TYPE) {
char code = ((Character) value).charValue();
if (!isValidCharCode(code)) {
writeln(createString(code));
return;
}
value = quoteCharCode(code);
if (value == null) {
value = Character.valueOf(code);
}
}
writeln("<" + primitiveTypeName + ">" + value + "</" +
primitiveTypeName + ">");
return;
}
} else if (value instanceof String) {
writeln(createString((String) value));
return;
}
if (d.name != null) {
writeln("<object idref=" + quote(d.name) + "/>");
return;
}
outputStatement(d.exp, outer, isArgument);
}
private static String quoteCharCode(int code) {
switch(code) {
case '&': return "&";
case '<': return "<";
case '>': return ">";
case '"': return """;
case '\'': return "'";
case '\r': return "
";
default: return null;
}
}
private static String createString(int code) {
return "<char code=\"#" + Integer.toString(code, 16) + "\"/>";
}
private String createString(String string) {
CharsetEncoder encoder = Charset.forName(encoding).newEncoder();
StringBuilder sb = new StringBuilder();
sb.append("<string>");
int index = 0;
while (index < string.length()) {
int point = string.codePointAt(index);
int count = Character.charCount(point);
if (isValidCharCode(point) && encoder.canEncode(string.substring(index, index + count))) {
String value = quoteCharCode(point);
if (value != null) {
sb.append(value);
} else {
sb.appendCodePoint(point);
}
index += count;
} else {
sb.append(createString(string.charAt(index)));
index++;
}
/*
String value = isValidCharCode(point) && encoder.canEncode(string.substring(index, index + count))
? quoteCharCode(point)
: createString(point);
if (value != null) {
sb.append(value);
} else {
sb.appendCodePoint(point);
}
index += count;
*/
}
sb.append("</string>");
return sb.toString();
}
private void outputStatement(Statement exp, Object outer, boolean isArgument) {
Object target = exp.getTarget();
String methodName = exp.getMethodName();
if (target == null || methodName == null) {
throw new NullPointerException((target == null ? "target" :
"methodName") + " should not be null");
}
Object[] args = exp.getArguments();
boolean expression = exp.getClass() == Expression.class;
Object value = (expression) ? getValue((Expression)exp) : null;
String tag = (expression && isArgument) ? "object" : "void";
String attributes = "";
ValueData d = getValueData(value);
if (expression) {
if (d.refs > 1) {
String instanceName = nameGenerator.instanceName(value);
d.name = instanceName;
attributes = attributes + " id=" + quote(instanceName);
}
}
// Special cases for targets.
if (target == outer) {
}
else if (target == Array.class && methodName.equals("newInstance")) {
tag = "array";
attributes = attributes + " class=" + quote(((Class)args[0]).getName());
attributes = attributes + " length=" + quote(args[1].toString());
args = new Object[]{};
}
else if (target.getClass() == Class.class) {
attributes = attributes + " class=" + quote(((Class)target).getName());
}
else {
d.refs = 2;
outputValue(target, outer, false);
outputValue(value, outer, false);
return;
}
// Special cases for methods.
if ((!expression && methodName.equals("set") && args.length == 2 &&
args[0] instanceof Integer) ||
(expression && methodName.equals("get") && args.length == 1 &&
args[0] instanceof Integer)) {
attributes = attributes + " index=" + quote(args[0].toString());
args = (args.length == 1) ? new Object[]{} : new Object[]{args[1]};
}
else if ((!expression && methodName.startsWith("set") && args.length == 1) ||
(expression && methodName.startsWith("get") && args.length == 0)) {
attributes = attributes + " property=" +
quote(Introspector.decapitalize(methodName.substring(3)));
}
else if (!methodName.equals("new") && !methodName.equals("newInstance")) {
attributes = attributes + " method=" + quote(methodName);
}
Vector statements = statementList(value);
// Use XML's short form when there is no body.
if (args.length == 0 && statements.size() == 0) {
writeln("<" + tag + attributes + "/>");
return;
}
writeln("<" + tag + attributes + ">");
indentation++;
for(int i = 0; i < args.length; i++) {
outputValue(args[i], null, true);
}
for(int i = 0; i < statements.size(); i++) {
Statement s = (Statement)statements.get(i);
outputStatement(s, value, false);
}
indentation--;
writeln("</" + tag + ">");
}
}
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