/*
* Copyright 1999,2004 The Apache Software Foundation.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.taglibs.standard.extra.spath;
import java.io.IOException;
import java.util.List;
import java.util.Stack;
import org.apache.xalan.serialize.Serializer;
import org.apache.xalan.serialize.SerializerFactory;
import org.apache.xalan.templates.OutputProperties;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.XMLFilter;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.XMLFilterImpl;
import org.xml.sax.helpers.XMLReaderFactory;
/**
* <p>Filters a SAX stream based on a single supplied SPath
* expression.</p>
*
* @author Shawn Bayern
*/
public class SPathFilter extends XMLFilterImpl {
//*********************************************************************
// Protected state
/** The steps in the SPath expression we use for filtering. */
protected List steps;
//*********************************************************************
// Private state in support of filtering
private int depth; // depth in parsed document
private Stack acceptedDepths; // depth of acceptance
private int excludedDepth; // depth of exclusion
private static final boolean DEBUG = false;
//*********************************************************************
// Main method (for testing)
/** Simple command-line interface, mostly for testing. */
public static void main(String args[])
throws ParseException, IOException, SAXException {
// temporary...
System.setProperty("org.xml.sax.driver", "org.apache.xerces.parsers.SAXParser");
// retrieve and parse the expression
String expr = args[0];
SPathParser s = new SPathParser(expr);
Path p = s.expression();
// construct the appropriate SAX chain
// (reader -> us -> serializer)
XMLReader r = XMLReaderFactory.createXMLReader();
XMLFilter f1 = new SPathFilter(p);
XMLFilter f2 = new XMLFilterImpl();
f1.setParent(r);
f2.setParent(f1);
Serializer sz = SerializerFactory.getSerializer
(OutputProperties.getDefaultMethodProperties("xml"));
sz.setOutputStream(System.out);
f2.setContentHandler(sz.asContentHandler());
// go!
f2.parse(new InputSource(System.in));
System.out.println();
}
//*********************************************************************
// Constructor and initialization methods
/** Constructs a new SPathFilter, given a Path. */
public SPathFilter(Path path) {
init();
this.steps = path.getSteps();
}
/** Initializes state used for filtering. */
private void init() {
depth = 0;
excludedDepth = -1;
acceptedDepths = new Stack();
}
//*********************************************************************
// ContentHandler methods
// startElement() and endElement() both require and modify filter
// state. They contain and direct the bulk of the filter's operation.
/** Filter for startElement(). */
public void startElement(String uri,
String localName,
String qName,
Attributes a) throws SAXException {
// always update the depth
depth++;
// if we're in an accepted section, simply pass through
if (isAccepted()) {
getContentHandler().startElement(uri, localName, qName, a);
return;
}
// likewise, if we're excluded, then simply block and return
if (isExcluded())
return;
// now, not accepted or excluded, let's see if we've got a match.
// we need to get the appropriate step based on the number of
// steps we've previously accepted
Step currentStep = (Step) steps.get(acceptedDepths.size());
if (nodeMatchesStep(currentStep, uri, localName, qName, a)) {
if (DEBUG)
System.err.println("*** Progressive match (" + acceptedDepths.size() + "): " + localName);
// new match (progressive)
acceptedDepths.push(new Integer(depth - 1));
// is it enough? give acceptance another chance...
if (isAccepted())
getContentHandler().startElement(uri, localName, qName, a);
} else if (!currentStep.isDepthUnlimited()) {
// if the step was preceded by '/' instead of '//', then
// we can't have a match at this node or beneath it
excludedDepth = depth - 1;
}
// nothing left to check; no reason to include node
return;
}
/** Filter for endElement(). */
public void endElement(String uri, String localName, String qName)
throws SAXException {
// reduce the depth
depth--;
if (isExcluded()) {
// determine if exclusion ends with us
if (excludedDepth == depth)
excludedDepth = -1;
// either way, we have been excluded, so pass nothing through
return;
}
// if we're excepted (for now), include ourselves...
if (isAccepted())
getContentHandler().endElement(uri, localName, qName);
if (DEBUG) {
System.err.println("*** Closing tag: " + localName);
System.err.println("*** acceptedDepths.size(): " + acceptedDepths.size());
System.err.println("*** last accepted depth: " + ((Integer)acceptedDepths.peek()).intValue());
System.err.println("*** depth: " + depth);
}
// now, back off if we correspond to a "successful" start tag
if (acceptedDepths.size() > 0 &&
(((Integer)acceptedDepths.peek()).intValue()) == depth)
acceptedDepths.pop();
}
// The remaining ContentHandler functions require only one bit of
// state: are we in a mode where we pass them through, or does
// the current state dictate that we ignore them. They need no other
// information and cannot have any effect on the current state.
/** Filter for ignoreableWhitespace(). */
public void ignorableWhitespace(char[] ch, int start, int length)
throws SAXException {
if (isAccepted())
getContentHandler().ignorableWhitespace(ch, start, length);
}
/** Filter for characters(). */
public void characters(char[] ch, int start, int length)
throws SAXException {
if (isAccepted())
getContentHandler().characters(ch, start, length);
}
/** Filter for startPrefixMapping(). */
public void startPrefixMapping(String prefix, String uri)
throws SAXException {
if (isAccepted())
getContentHandler().startPrefixMapping(prefix, uri);
}
/** Filter for endPrefixMapping(). */
public void endPrefixMapping(String prefix)
throws SAXException {
if (isAccepted())
getContentHandler().endPrefixMapping(prefix);
}
/** Filter for processingInstruction(). */
public void processingInstruction(String target, String data)
throws SAXException {
if (isAccepted())
getContentHandler().processingInstruction(target, data);
}
/** Filter for skippedEntity(). */
public void skippedEntity(String name) throws SAXException {
if (isAccepted())
getContentHandler().skippedEntity(name);
}
// We reset state in startDocument(), in case we're reused
/** Resets state. */
public void startDocument() {
init();
}
//*********************************************************************
// Private utility methods
public static boolean nodeMatchesStep(Step s,
String uri,
String localName,
String qName,
Attributes a) {
// if the name doesn't match, then we've got a loser
if (!s.isMatchingName(uri, localName))
return false;
// it's still in the game; check the predicates
List l = s.getPredicates();
for (int i = 0; l != null && i < l.size(); i++) {
Predicate p = (Predicate) l.get(i);
if (!(p instanceof AttributePredicate))
throw new UnsupportedOperationException
("only attribute predicates are supported by filter");
if (!((AttributePredicate) p).isMatchingAttribute(a))
return false; // all predicates must match
}
// it's survived
return true;
}
/** Returns true if events should be passed through, false otherwise. */
private boolean isAccepted() {
return (acceptedDepths.size() >= steps.size());
}
/** Returns true if events should be blocked, false otherwise. */
private boolean isExcluded() {
return (excludedDepth != -1);
}
}