Error handling should be simple if you remember that exceptions * you throw will cancel later stages in that callback's pipeline, and * generally the producer will stop if it sees such an exception. You * may want to protect your pipeline against such backflows, making a * kind of reverse filter (or valve?) so that certain exceptions thrown by * your pipeline will caught and handled before the producer sees them. * Just use a "try/catch" block, rememebering that really important * cleanup tasks should be in "finally" clauses. * *
That issue isn't unique to "tee" consumers, but tee consumers have * the additional twist that exceptions thrown by the first consumer * will cause the second consumer not to see the callback (except for * the endDocument callback, which signals state cleanup). * * @author David Brownell * @version $Date: 2002/09/30 15:08:52 $ */ final public class TeeConsumer implements EventConsumer, ContentHandler, DTDHandler, LexicalHandler,DeclHandler { private EventConsumer first, rest; // cached to minimize time overhead private ContentHandler docFirst, docRest; private DeclHandler declFirst, declRest; private LexicalHandler lexFirst, lexRest; /** * Constructs a consumer which sends all its events to the first * consumer, and then the second one. If the first consumer throws * an exception, the second one will not see the event which * caused that exception to be reported. * * @param car The first consumer to get the events * @param cdr The second consumer to get the events */ public TeeConsumer (EventConsumer car, EventConsumer cdr) { if (car == null || cdr == null) throw new NullPointerException (); first = car; rest = cdr; // // Cache the handlers. // docFirst = first.getContentHandler (); docRest = rest.getContentHandler (); // DTD handler isn't cached (rarely needed) try { declFirst = null; declFirst = (DeclHandler) first.getProperty ( EventFilter.HANDLER_URI + "declaration-handler"); } catch (SAXException e) {} try { declRest = null; declRest = (DeclHandler) rest.getProperty ( EventFilter.HANDLER_URI + "declaration-handler"); } catch (SAXException e) {} try { lexFirst = null; lexFirst = (LexicalHandler) first.getProperty ( EventFilter.HANDLER_URI + "lexical-handler"); } catch (SAXException e) {} try { lexRest = null; lexRest = (LexicalHandler) rest.getProperty ( EventFilter.HANDLER_URI + "lexical-handler"); } catch (SAXException e) {} } /** * Constructs a pipeline, and is otherwise a shorthand for the * two-consumer constructor for this class. * * @param first Description of the first pipeline to get events, * which will be passed to {@link PipelineFactory#createPipeline} * @param rest The second pipeline to get the events */ // constructor used by PipelineFactory public TeeConsumer (String first, EventConsumer rest) throws IOException { this (PipelineFactory.createPipeline (first), rest); } /** Returns the first pipeline to get event calls. */ public EventConsumer getFirst () { return first; } /** Returns the second pipeline to get event calls. */ public EventConsumer getRest () { return rest; } /** Returns the content handler being used. */ final public ContentHandler getContentHandler () { if (docRest == null) return docFirst; if (docFirst == null) return docRest; return this; } /** Returns the dtd handler being used. */ final public DTDHandler getDTDHandler () { // not cached (hardly used) if (rest.getDTDHandler () == null) return first.getDTDHandler (); if (first.getDTDHandler () == null) return rest.getDTDHandler (); return this; } /** Returns the declaration or lexical handler being used. */ final public Object getProperty (String id) throws SAXNotRecognizedException { // // in degenerate cases, we have no work to do. // Object firstProp = null, restProp = null; try { firstProp = first.getProperty (id); } catch (SAXNotRecognizedException e) { /* ignore */ } try { restProp = rest.getProperty (id); } catch (SAXNotRecognizedException e) { /* ignore */ } if (restProp == null) return firstProp; if (firstProp == null) return restProp; // // we've got work to do; handle two builtin cases. // if ((EventFilter.HANDLER_URI + "declaration-handler").equals (id)) return this; if ((EventFilter.HANDLER_URI + "lexical-handler").equals (id)) return this; // // non-degenerate, handled by both consumers, but we don't know // how to handle this. // throw new SAXNotRecognizedException ("can't tee: " + id); } /** * Provides the error handler to both subsequent nodes of * this filter stage. */ public void setErrorHandler (ErrorHandler handler) { first.setErrorHandler (handler); rest.setErrorHandler (handler); } // // ContentHandler // public void setDocumentLocator (Locator l) { // this call is not made by all parsers docFirst.setDocumentLocator (l); docRest.setDocumentLocator (l); } public void startDocument () throws SAXException { docFirst.startDocument (); docRest.startDocument (); } public void endDocument () throws SAXException { try { docFirst.endDocument (); } finally { docRest.endDocument (); } } public void startPrefixMapping (String prefix, String uri) throws SAXException { docFirst.startPrefixMapping (prefix, uri); docRest.startPrefixMapping (prefix, uri); } public void endPrefixMapping (String prefix) throws SAXException { docFirst.endPrefixMapping (prefix); docRest.endPrefixMapping (prefix); } public void skippedEntity (String name) throws SAXException { docFirst.skippedEntity (name); docRest.skippedEntity (name); } public void startElement (String uri, String local, String name, Attributes atts) throws SAXException { docFirst.startElement (uri, local, name, atts); docRest.startElement (uri, local, name, atts); } public void endElement (String uri, String local, String name) throws SAXException { docFirst.endElement (uri, local, name); docRest.endElement (uri, local, name); } public void processingInstruction (String target, String data) throws SAXException { docFirst.processingInstruction (target, data); docRest.processingInstruction (target, data); } public void characters (char buf [], int off, int len) throws SAXException { docFirst.characters (buf, off, len); docRest.characters (buf, off, len); } public void ignorableWhitespace (char buf [], int off, int len) throws SAXException { docFirst.ignorableWhitespace (buf, off, len); docRest.ignorableWhitespace (buf, off, len); } // // DTDHandler // public void notationDecl (String name, String pubid, String sysid) throws SAXException { DTDHandler l1 = first.getDTDHandler (); DTDHandler l2 = rest.getDTDHandler (); l1.notationDecl (name, pubid, sysid); l2.notationDecl (name, pubid, sysid); } public void unparsedEntityDecl (String name, String pubid, String sysid, String ndata ) throws SAXException { DTDHandler l1 = first.getDTDHandler (); DTDHandler l2 = rest.getDTDHandler (); l1.unparsedEntityDecl (name, pubid, sysid, ndata); l2.unparsedEntityDecl (name, pubid, sysid, ndata); } // // DeclHandler // public void attributeDecl (String element, String attribute, String type, String valueDefault, String value) throws SAXException { declFirst.attributeDecl (element, attribute, type, valueDefault, value); declRest.attributeDecl (element, attribute, type, valueDefault, value); } public void elementDecl (String element, String model) throws SAXException { declFirst.elementDecl (element, model); declRest.elementDecl (element, model); } public void externalEntityDecl (String entity, String publicId, String systemId) throws SAXException { declFirst.externalEntityDecl (entity, publicId, systemId); declRest.externalEntityDecl (entity, publicId, systemId); } public void internalEntityDecl (String entity, String value) throws SAXException { declFirst.internalEntityDecl (entity, value); declRest.internalEntityDecl (entity, value); } // // LexicalHandler // public void comment (char buf [], int off, int len) throws SAXException { lexFirst.comment (buf, off, len); lexRest.comment (buf, off, len); } public void startCDATA () throws SAXException { lexFirst.startCDATA (); lexRest.startCDATA (); } public void endCDATA () throws SAXException { lexFirst.endCDATA (); lexRest.endCDATA (); } public void startEntity (String name) throws SAXException { lexFirst.startEntity (name); lexRest.startEntity (name); } public void endEntity (String name) throws SAXException { lexFirst.endEntity (name); lexRest.endEntity (name); } public void startDTD (String name, String pubid, String sysid) throws SAXException { lexFirst.startDTD (name, pubid, sysid); lexRest.startDTD (name, pubid, sysid); } public void endDTD () throws SAXException { lexFirst.endDTD (); lexRest.endDTD (); } }