XMLEncoder.java revision 2362
/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* 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.
*/
/**
* 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
* 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
*
* @author Philip Milne
*/
public class XMLEncoder extends Encoder {
private final CharsetEncoder encoder;
private final boolean declaration;
private OutputStreamWriter out;
private int indentation = 0;
private boolean internal = false;
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.
}
/**
* Creates a new XML encoder to write out <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 written
*
* @throws IllegalArgumentException
* if <code>out</code> is <code>null</code>
*
* @see XMLDecoder#XMLDecoder(InputStream)
*/
}
/**
* Creates a new XML encoder to write out <em>JavaBeans</em>
* to the stream <code>out</code> using the given <code>charset</code>
* starting from the given <code>indentation</code>.
*
* @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</code>
* 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</code> or <code>charset</code> is <code>null</code>,
* or if <code>indentation</code> is less than 0
*
* @throws IllegalCharsetNameException
* if <code>charset</code> 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
*/
throw new IllegalArgumentException("the output stream cannot be null");
}
if (indentation < 0) {
throw new IllegalArgumentException("the indentation must be >= 0");
}
this.declaration = declaration;
this.indentation = indentation;
nameGenerator = new NameGenerator();
}
/**
* Sets the owner of this encoder to <code>owner</code>.
*
* @param owner The owner of this encoder.
*
* @see #getOwner
*/
}
/**
* Gets the owner of this encoder.
*
* @return The owner of this encoder.
*
* @see #setOwner
*/
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 {
}
}
}
return list;
}
if (o == null || o == this) {
return;
}
ValueData d = getValueData(o);
// Do not mark liternal strings. Other strings, which might,
// for example, come from resource bundles should still be marked.
return;
}
// Bump the reference counts of all arguments
if (isArgument) {
d.refs++;
}
if (d.marked) {
return;
}
d.marked = true;
// Pending: Why does the reference count need to
// be incremented here?
d.refs++;
}
}
}
}
/**
* 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
*/
// System.out.println("XMLEncoder::writeStatement: " + oldStm);
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);
*/
}
catch (Exception e) {
getExceptionListener().exceptionThrown(new Exception("XMLEncoder: discarding statement " + oldStm, e));
}
}
/**
* 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
*
* @param oldExp The expression that will be written
* to the stream.
* @see java.beans.PersistenceDelegate#initialize
*/
this.internal = true;
super.writeExpression(oldExp);
}
}
/**
* 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.
if (this.declaration) {
}
preambleWritten = true;
}
indentation++;
while (!statements.isEmpty()) {
}
else {
outputStatement(s, this, false);
}
}
indentation--;
try {
}
catch (IOException e) {
}
clear();
}
void clear() {
super.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 {
}
catch (IOException e) {
}
}
return "\"" + s + "\"";
}
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) {
|| (0x000A == code)
|| (0x0009 == code)
|| (0x000D == code)
}
try {
for(int i = 0; i < indentation; i++) {
}
}
catch (IOException e) {
}
}
writeln("<null/>");
return;
}
return;
}
"methodName") + " should not be null");
}
return;
}
// Make sure that character types are quoted correctly.
if (!isValidCharCode(code)) {
return;
}
}
}
primitiveTypeName + ">");
return;
}
return;
}
}
}
}
switch(code) {
case '&': return "&";
case '<': return "<";
case '>': return ">";
case '"': return """;
case '\'': return "'";
case '\r': return " ";
default: return null;
}
}
}
int index = 0;
} else {
}
} else {
index++;
}
}
}
"methodName") + " should not be null");
}
// Special cases for targets.
}
tag = "array";
}
}
else {
d.refs = 2;
}
return;
}
d.name = instanceName;
}
// Special cases for methods.
}
}
}
}
// Use XML's short form when there is no body.
return;
}
indentation++;
}
while (!statements.isEmpty()) {
outputStatement(s, value, false);
}
indentation--;
}
}