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jeremybenn |
/* gnu.java.beans.decoder.AbstractElementHandler
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Copyright (C) 2004 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package gnu.java.beans.decoder;
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import java.beans.ExceptionListener;
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import org.xml.sax.Attributes;
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/** ElementHandler manages a Context instance and interacts with
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* its parent and child handlers.
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*
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* @author Robert Schuster
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*/
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abstract class AbstractElementHandler implements ElementHandler
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{
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/** The Context instance of this handler. The instance is available after the startElement()
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* method was called. Otherwise the handler is marked as failed.
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*/
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private Context context;
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/** The parent handler. */
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private ElementHandler parent;
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/** Stores whether this handler is marked as failed. */
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private boolean hasFailed;
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/** Stores the character data which is contained in the body of the XML tag. */
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private StringBuffer buffer = new StringBuffer();
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/** Stores whether this ElementHandler can have subelements. The information for this is taken from
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* javabeans.dtd which can be found here:
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* <a href="http://java.sun.com/products/jfc/tsc/articles/persistence3/">Java Persistence Article</a>
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*/
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private boolean allowsSubelements;
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/** Creates a new ElementHandler with the given ElementHandler instance
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* as parent.
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*
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* @param parentHandler The parent handler.
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*/
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protected AbstractElementHandler(ElementHandler parentHandler,
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boolean allowsSubs)
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{
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parent = parentHandler;
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allowsSubelements = allowsSubs;
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}
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/** Evaluates the attributes and creates a Context instance.
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* If the creation of the Context instance fails the ElementHandler
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* is marked as failed which may affect the parent handler other.
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*
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* @param attributes Attributes of the XML tag.
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*/
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public final void start(Attributes attributes,
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ExceptionListener exceptionListener)
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{
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try
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{
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// lets the subclass create the appropriate Context instance
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context = startElement(attributes, exceptionListener);
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}
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catch (AssemblyException pe)
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{
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Throwable t = pe.getCause();
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if (t instanceof Exception)
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exceptionListener.exceptionThrown((Exception) t);
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else
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throw new InternalError("Unexpected Throwable type in AssemblerException. Please file a bug report.");
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notifyContextFailed();
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return;
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}
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}
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/** Analyses the content of the Attributes instance and creates a Context
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* object accordingly.
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* An AssemblerException is thrown when the Context instance could not
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* be created.
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*
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* @param attributes Attributes of the XML tag.
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* @return A Context instance.
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* @throws AssemblerException when Context instance could not be created.
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*/
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protected abstract Context startElement(Attributes attributes, ExceptionListener exceptionListener)
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throws AssemblyException;
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/** Post-processes the Context.
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*/
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public final void end(ExceptionListener exceptionListener)
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{
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// skips processing if the handler is marked as failed (because the Context
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// is then invalid or may not exist at all)
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if (!hasFailed)
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{
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try
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{
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// note: the order of operations is very important here
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// sends the stored character data to the Context
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endElement(buffer.toString());
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// reports to the parent handler if this handler's Context is a
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// statement (returning no value BACK to the parent's Context)
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if (context.isStatement())
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{
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// This may create a valid result in the parent's Context
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// or let it fail
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parent.notifyStatement(exceptionListener);
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// skips any further processing if the parent handler is now marked
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// as failed
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if (parent.hasFailed())
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return;
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}
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// processes the Context and stores the result
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putObject(context.getId(), context.endContext(parent.getContext()));
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// transfers the Context's results to the parent's Context
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// if it is an expression (rather than a statement)
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if (! context.isStatement())
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parent.getContext().addParameterObject(context.getResult());
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}
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catch (AssemblyException pe)
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{
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// notifies that an exception was thrown in this handler's Context
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Throwable t = pe.getCause();
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if (t instanceof Exception)
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exceptionListener.exceptionThrown((Exception) t);
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else
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throw (InternalError) new InternalError("Severe problem while decoding XML data.")
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.initCause(t);
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// marks the handler as failed
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notifyContextFailed();
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}
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}
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}
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/** Notifies the handler's Context that its child Context will not return
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* a value back. Some Context variants need this information to know when
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* a method or a constructor call can be made.
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*
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* This method is called by a child handler.
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*/
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public void notifyStatement(ExceptionListener exceptionListener)
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{
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try
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{
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// propagates to parent handler first to generate objects
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// needed by this Context instance
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if(context.isStatement())
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{
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parent.notifyStatement(exceptionListener);
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}
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// Some Context instances do stuff which can fail now. If that
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// happens this handler is marked as failed.
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context.notifyStatement(parent.getContext());
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}
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catch (AssemblyException ae)
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{
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// notifies that an exception was thrown in this handler's Context
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Throwable t = ae.getCause();
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if (t instanceof Exception)
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exceptionListener.exceptionThrown((Exception) t);
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else
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throw (InternalError) new InternalError("Severe problem while decoding XML data.")
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.initCause(t);
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// marks the handler as failed
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notifyContextFailed();
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}
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}
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/** Marks this and any depending parent handlers as failed. Which means that on their end
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* no result is calculated.
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*
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* When a handler has failed no more handlers are accepted within it.
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*/
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public final void notifyContextFailed()
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{
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hasFailed = true;
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// marks the parent handler as failed if its Context
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// is affected by the failure of this handler's Context
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if (parent.getContext().subContextFailed())
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parent.notifyContextFailed();
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}
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/** Returns whether this handler has failed.
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*
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* This is used to skip child elements.
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*
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* @return Whether this handler has failed.
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*/
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public final boolean hasFailed()
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{
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return hasFailed;
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}
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/** Processes the character data when the element ends.
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*
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* The default implementation does nothing for convenience.
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*
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* @param characters
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* @throws AssemblerException
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*/
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protected void endElement(String characters) throws AssemblyException
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{
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// XXX: throw an exception when unexpected character data is available?
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}
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/** Adds characters from the body of the XML tag to the buffer.
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*
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* @param ch
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* @param start
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* @param length
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* @throws SAXException
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*/
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public final void characters(char[] ch, int start, int length)
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{
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// simply appends character data
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buffer.append(ch, start, length);
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}
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/** Stores an object globally under a unique id. If the id is
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* null the object is not stored.
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*
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* @param objectId
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* @param o
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*/
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public void putObject(String objectId, Object o)
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{
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if (objectId != null)
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parent.putObject(objectId, o);
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}
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/** Returns a previously stored object. If the id is null the
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* result is null, too.
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*
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* @param objectId
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* @return Returns a previously stored object or null.
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*/
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public Object getObject(String objectId) throws AssemblyException
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{
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return objectId == null ? null : parent.getObject(objectId);
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}
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/** Returns the Class instance as if called Class.forName() but
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* uses a ClassLoader given by the user.
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*
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* @param className
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* @return
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* @throws ClassNotFoundException
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*/
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public Class instantiateClass(String className)
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throws ClassNotFoundException
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{
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return parent.instantiateClass(className);
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}
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public final boolean isSubelementAllowed(String subElementName)
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{
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return allowsSubelements && ! subElementName.equals("java");
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}
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public final Context getContext()
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{
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return context;
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}
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public final ElementHandler getParent()
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{
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return parent;
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}
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}
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