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Diffstat (limited to 'libjava/java/beans/XMLDecoder.java')
| -rw-r--r-- | libjava/java/beans/XMLDecoder.java | 307 |
1 files changed, 307 insertions, 0 deletions
diff --git a/libjava/java/beans/XMLDecoder.java b/libjava/java/beans/XMLDecoder.java new file mode 100644 index 00000000000..87703352248 --- /dev/null +++ b/libjava/java/beans/XMLDecoder.java @@ -0,0 +1,307 @@ +/* java.beans.XMLDecoder -- + Copyright (C) 2004, 2005 Free Software Foundation, Inc. + +This file is part of GNU Classpath. + +GNU Classpath is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2, or (at your option) +any later version. + +GNU Classpath 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 for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; see the file COPYING. If not, write to the +Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA +02111-1307 USA. + +Linking this library statically or dynamically with other modules is +making a combined work based on this library. Thus, the terms and +conditions of the GNU General Public License cover the whole +combination. + +As a special exception, the copyright holders of this library give you +permission to link this library with independent modules to produce an +executable, regardless of the license terms of these independent +modules, and to copy and distribute the resulting executable under +terms of your choice, provided that you also meet, for each linked +independent module, the terms and conditions of the license of that +module. An independent module is a module which is not derived from +or based on this library. If you modify this library, you may extend +this exception to your version of the library, but you are not +obligated to do so. If you do not wish to do so, delete this +exception statement from your version. */ + + +package java.beans; + +import gnu.java.beans.decoder.DefaultExceptionListener; +import gnu.java.beans.decoder.PersistenceParser; + +import java.io.IOException; +import java.io.InputStream; +import java.util.Iterator; +import java.util.NoSuchElementException; + +/** + * The XMLDecoder reads XML data that is structured according to + * <a href="http://java.sun.com/products/jfc/tsc/articles/persistence3/javabeans.dtd">this</a> DTD + * and creates objects according to the content. Usually such data is generated using the + * {@link XMLEncoder} class. + * <p> + * An example XML document might look like this: + * <code> + * <java> + * <string>Hello World</string> + * <int>200</int> + * </java> + * </code> + * <p>To read the <code>String</code> and the <code>Integer</code> instance the following can be used (assume + * the XML data can be obtained from the InputStream):</p> + * <code> + * XMLDecoder decoder = new XMLDecoder(inputStreamContainingXMLData); + * String message = (String) decoder.readObject(); + * Integer number = (Integer) decoder.readObject(); + * </code> + * <p>Besides this basic functionality the <code>XMLDecoder</code> has some more features that might come + * handy in certain situations:</p> + * <p>An owner object can be set using the <code>setOwner</code> method which can then be accessed when + * decoding. This feature is only useful if the XML data is aware of the owner object. Such data may + * look like this (assume that the owner object is a JFrame instance):</p> + * <code> + * <java> + * <void method="getOwner"> + * <void method="setVisible"> + * <boolean>true<boolean> + * </void> + * </void> + * </java> + * </code> + * This accesses the <code>JFrame</code> and makes it visible using the <code>setVisible</code> method. + * <p>Please note that changing the owner <b>after</b> the having read the first object has no effect, + * because all object have been decoded then.</p> + * <p>If the <code>XMLDecoder</code> is created with no {@link ExceptionListener} instance a default one + * is used that prints an error message to <code>System.err</code> whenever a recoverable exception + * is thrown. Recovarable exceptions occur when the XML data cannot be interpreted correctly (e.g + * unknown classes or methods, invocation on null, ...). In general be very careful when the + * <code>XMLDecoder</code> provoked such exceptions because the resulting object(s) may be in an + * undesirable state.</p> + * <p>Note that changing the ExceptionListener instance after <code>readObject</code> has been called + * once has no effect because the decoding is completed then.</p> + * <p>At last one can provide a specific <code>ClassLoader</code> which is then used when <code>Class</code> + * objects are accessed. See {@link java.lang.Class#forName(String, boolean, ClassLoader)} for details + * on this.</p> + * <p>Note: If the <code>InputStream</code> instance given to any of the constructors is <code>null</code> + * the resulting <code>XMLDecoder</code> will be silently (without any exception) useless. Each call + * to <code>readObject</code> will return <code>null</code> and never throws an + * <code>ArrayIndexOutOfBoundsException</code>.</p> + * + * @author Robert Schuster + * @since 1.4 + * @status updated to 1.5 + */ +public class XMLDecoder +{ + private Object owner; + + private ExceptionListener exceptionListener; + + private InputStream inputStream; + + private boolean isStreamClosed; + + private ClassLoader classLoader; + + private Iterator iterator; + + /** Creates a XMLDecoder instance that parses the XML data of the given input stream. + * Using this constructor no special ClassLoader, a default ExceptionListener + * and no owner object is used. + * + * @param in InputStream to read XML data from. + */ + public XMLDecoder(InputStream in) + { + this(in, null); + } + + /** Creates a XMLDecoder instance that parses the XML data of the given input stream. + * Using this constructor no special ClassLoader and a default ExceptionListener + * is used. + * + * @param in InputStream to read XML data from. + * @param owner Owner object which can be accessed and modified while parsing. + */ + public XMLDecoder(InputStream in, Object owner) + { + this(in, owner, null); + } + + /** Creates a XMLDecoder instance that parses the XML data of the given input stream. + * If the ExceptionListener argument is null a default implementation is used. + * + * @param in InputStream to read XML data from. + * @param owner Owner object which can be accessed and modified while parsing. + * @param exceptionListener ExceptionListener instance to which exception notifications are send. + */ + public XMLDecoder( + InputStream in, + Object owner, + ExceptionListener exceptionListener) + { + this( + in, + owner, + exceptionListener, + Thread.currentThread().getContextClassLoader()); + } + + /** Creates a XMLDecoder instance that parses the XML data of the given input stream. + * If the ExceptionListener argument is null a default implementation is used. + * + * @param in InputStream to read XML data from. + * @param owner Owner object which can be accessed and modified while parsing. + * @param exceptionListener ExceptionListener instance to which exception notifications are send. + * @param cl ClassLoader instance that is used for calls to <code>Class.forName(String, boolean, ClassLoader)</code> + * @since 1.5 + */ + public XMLDecoder( + InputStream in, + Object owner, + ExceptionListener listener, + ClassLoader cl) + { + // initially here was a check for the validity of the InputStream argument but some + // great engineers decided that this API should silently discard this and behave rather + // odd: readObject will always return null ... + inputStream = in; + + setExceptionListener(listener); + + // validity of this object is checked in Class.forName() and therefore may be null + classLoader = cl; + + this.owner = owner; + } + + /** Closes the stream associated with this decoder. This should be done after having read all + * decoded objects. + * <p>See the description of the {@link #readObject()} for the effect caused by <code>close</code>.</p> + */ + public void close() + { + if (isStreamClosed) + { + return; + } + + try + { + inputStream.close(); + isStreamClosed = true; + } + catch (IOException e) + { + // bad style forced by original API design ... + } + } + + /** Returns the ExceptionListener instance associated with this decoder. + * <p>See the description of {@link XMLDecoder} class for more information on the ExceptionListener.</p> + * + * @return Current ExceptionListener of the decoder. + */ + public ExceptionListener getExceptionListener() + { + return exceptionListener; + } + + /** Returns the owner object of the decoder. This method is usually called + * from within the parsed XML data. + * <p>See the description of {@link XMLDecoder} class for more information on the owner object.</p> + * + * @return The owner object of this decoder. + */ + public Object getOwner() + { + return owner; + } + + /** Returns the next available decoded object. + * <p>Note that the actual decoding takes place when the method is called for the first time.</p> + * <p>If the <code>close</code> method was already called a <code>NoSuchElementException</code> + * is thrown.</p> + * <p>If the InputStream instance used in the constructors was <code>null</code> this method + * will always return <code>null</code> itself.</p> + * + * @return The next object in a sequence decoded from XML data. + * @throws ArrayIndexOutOfBoundsException When no more objects are available. + */ + public Object readObject() throws ArrayIndexOutOfBoundsException + { + // note: the RI does it this way ... + if(inputStream == null) { + return null; + } + + // note: the original API documentation says nothing on what to do + // when the stream was closed before readObject is called but it actually + // throws a NoSuchElementException - this behaviour is imitated here + if (isStreamClosed) + { + throw new NoSuchElementException("Cannot read any objects - XMLDecoder was already closed."); + } + + // creates the PersistenceParser (doing the parsing and decoding) and returns its + // Iterator on first invocation + if (iterator == null) + { + iterator = + new PersistenceParser( + inputStream, + exceptionListener, + classLoader, + this) + .iterator(); + } + + // note: done according to the official documentation + if (!iterator.hasNext()) + { + throw new ArrayIndexOutOfBoundsException("No more objects available from this XMLDecoder."); + } + + // returns just the next object if there was no problem + return iterator.next(); + } + + /** Sets the ExceptionListener instance to which notifications of exceptions are send + * while parsing the XML data. + * <p>See the description of {@link XMLDecoder} class for more information on the ExceptionListener.</p> + * + * @param listener + */ + public void setExceptionListener(ExceptionListener listener) + { + // uses a default implementation when null + if (listener == null) + { + listener = new DefaultExceptionListener(); + } + exceptionListener = listener; + } + + /** Sets the owner object which can be accessed from the parsed XML data. + * <p>See the description of {@link XMLDecoder} class for more information on the owner object.</p> + * + * @param newOwner + */ + public void setOwner(Object newOwner) + { + owner = newOwner; + } + +} |