|
|
Java example source code file (XMLEncoder.java)
This example Java source code file (XMLEncoder.java) is included in the alvinalexander.com
"Java Source Code
Warehouse" project. The intent of this project is to help you "Learn
Java by Example" TM.
Learn more about this Java project at its project page.
The XMLEncoder.java Java example source code
/*
* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/
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.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
/**
* The <code>XMLEncoder class is a complementary alternative to
* the <code>ObjectOutputStream and can used to generate
* a textual representation of a <em>JavaBean in the same
* way that the <code>ObjectOutputStream can
* be used to create binary representation of <code>Serializable
* objects. For example, the following fragment can be used to create
* a textual representation the supplied <em>JavaBean
* 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
* class is exclusively designed for the purpose of archiving graphs
* of <em>JavaBeans 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 continues to be recommended
* for interprocess communication and general purpose serialization.
* <p>
* The <code>XMLEncoder class provides a default denotation for
* <em>JavaBeans 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 class are:
* <ul>
* <li>
* <em>Portable and version resilient: 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: The XMLEncoder class
* uses a <em>redundancy elimination algorithm internally so that the
* default values of a Bean's properties are not written to the stream.
* <li>
* <em>Fault tolerant: 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 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 whose value is
* to be used as the argument to the enclosing element.
* <li>
* The "void" tag denotes a <em>statement 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 class could be written:
* <int>123</int>. Note that the <code>XMLEncoder 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 class
* itself deals only with <code>Objects.
* <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.
* @see XMLDecoder
* @see java.io.ObjectOutputStream
*
* @since 1.4
*
* @author Philip Milne
*/
public class XMLEncoder extends Encoder implements AutoCloseable {
private final CharsetEncoder encoder;
private final String charset;
private final boolean declaration;
private OutputStreamWriter out;
private Object owner;
private int indentation = 0;
private boolean internal = false;
private Map<Object, ValueData> valueToExpression;
private Map<Object, List 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 XML encoder to write out <em>JavaBeans
* to the stream <code>out using an XML encoding.
*
* @param out the stream to which the XML representation of
* the objects will be written
*
* @throws IllegalArgumentException
* if <code>out is null
*
* @see XMLDecoder#XMLDecoder(InputStream)
*/
public XMLEncoder(OutputStream out) {
this(out, "UTF-8", true, 0);
}
/**
* Creates a new XML encoder to write out <em>JavaBeans
* to the stream <code>out using the given charset
* starting from the given <code>indentation.
*
* @param out the stream to which the XML representation of
* the objects will be written
* @param charset the name of the requested charset;
* may be either a canonical name or an alias
* @param declaration whether the XML declaration should be generated;
* set this to <code>false
* when embedding the contents in another XML document
* @param indentation the number of space characters to indent the entire XML document by
*
* @throws IllegalArgumentException
* if <code>out or charset is null,
* or if <code>indentation is less than 0
*
* @throws IllegalCharsetNameException
* if <code>charset name is illegal
*
* @throws UnsupportedCharsetException
* if no support for the named charset is available
* in this instance of the Java virtual machine
*
* @throws UnsupportedOperationException
* if loaded charset does not support encoding
*
* @see Charset#forName(String)
*
* @since 1.7
*/
public XMLEncoder(OutputStream out, String charset, boolean declaration, int indentation) {
if (out == null) {
throw new IllegalArgumentException("the output stream cannot be null");
}
if (indentation < 0) {
throw new IllegalArgumentException("the indentation must be >= 0");
}
Charset cs = Charset.forName(charset);
this.encoder = cs.newEncoder();
this.charset = charset;
this.declaration = declaration;
this.indentation = indentation;
this.out = new OutputStreamWriter(out, cs.newEncoder());
valueToExpression = new IdentityHashMap<>();
targetToStatementList = new IdentityHashMap<>();
nameGenerator = new NameGenerator();
}
/**
* Sets the owner of this encoder to <code>owner.
*
* @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 List<Statement> statementList(Object target) {
List<Statement> list = targetToStatementList.get(target);
if (list == null) {
list = new ArrayList<>();
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();
mark(exp);
if (!(target instanceof Class)) {
statementList(target).add(exp);
// Pending: Why does the reference count need to
// be incremented here?
d.refs++;
}
}
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(), stm instanceof Expression);
}
/**
* 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);
Object target = oldStm.getTarget();
if (target instanceof Field) {
String method = oldStm.getMethodName();
Object[] args = oldStm.getArguments();
if ((method == null) || (args == null)) {
}
else if (method.equals("get") && (args.length == 1)) {
target = args[0];
}
else if (method.equals("set") && (args.length == 2)) {
target = args[0];
}
}
statementList(target).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
* 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.
if (this.declaration) {
writeln("<?xml version=" + quote("1.0") +
" encoding=" + quote(this.charset) + "?>");
}
writeln("<java version=" + quote(System.getProperty("java.version")) +
" class=" + quote(XMLDecoder.class.getName()) + ">");
preambleWritten = true;
}
indentation++;
List<Statement> statements = statementList(this);
while (!statements.isEmpty()) {
Statement s = statements.remove(0);
if ("writeObject".equals(s.getMethodName())) {
outputValue(s.getArguments()[0], this, true);
}
else {
outputStatement(s, this, false);
}
}
indentation--;
Statement statement = getMissedStatement();
while (statement != null) {
outputStatement(statement, this, false);
statement = getMissedStatement();
}
try {
out.flush();
}
catch (IOException e) {
getExceptionListener().exceptionThrown(e);
}
clear();
}
void clear() {
super.clear();
nameGenerator.clear();
valueToExpression.clear();
targetToStatementList.clear();
}
Statement getMissedStatement() {
for (List<Statement> statements : this.targetToStatementList.values()) {
for (int i = 0; i < statements.size(); i++) {
if (Statement.class == statements.get(i).getClass()) {
return statements.remove(i);
}
}
}
return null;
}
/**
* This method calls <code>flush, 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 = valueToExpression.get(o);
if (d == null) {
d = new ValueData();
valueToExpression.put(o, d);
}
return d;
}
/**
* Returns <code>true 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 can be combined
* to encode Unicode code point in documents containing only Unicode.
* (The <code>char 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 if the Unicode code point is valid,
* <code>false 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 {
StringBuilder sb = new StringBuilder();
for(int i = 0; i < indentation; i++) {
sb.append(' ');
}
sb.append(exp);
sb.append('\n');
this.out.write(sb.toString());
}
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() + "");
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 (isArgument && target instanceof Field && methodName.equals("get")) {
Field f = (Field)target;
writeln("<object class=" + quote(f.getDeclaringClass().getName()) +
" field=" + quote(f.getName()) + "/>");
return;
}
Class<?> primitiveType = 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 + "
Other Java examples (source code examples)
Here is a short list of links related to this Java XMLEncoder.java source code file:
|
The search page
Other Java source code examples at this package level
Click here to learn more about this project
