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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.jackrabbit.commons.xml;
import java.io.OutputStream;
import java.io.StringWriter;
import java.io.Writer;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.sax.TransformerHandler;
import javax.xml.transform.stream.StreamResult;
import org.xml.sax.Attributes;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.AttributesImpl;
import org.xml.sax.helpers.DefaultHandler;
/**
* A {@link ContentHandler} that serializes SAX events to a given
* {@link Result} instance. The JAXP {@link SAXTransformerFactory}
* facility is used for the serialization.
*
* This class explicitly ensures that all namespace prefixes are also
* present as xmlns attributes in the serialized XML document. This avoids
* problems with Xalan's serialization behaviour which was (at least during
* JDK 1.4) to ignore namespaces if they were not present as xmlns attributes.
*
* NOTE: The code in this class was originally written for Apache Cocoon and
* is included with some modifications here in Apache Jackrabbit. See the
* org.apache.cocoon.serialization.AbstractTextSerializer class in the
* cocoon-pipeline-impl component for the original code.
*
* @since Jackrabbit JCR Commons 1.5
*/
public class SerializingContentHandler extends DefaultContentHandler {
/**
* The character encoding used for serialization (UTF-8).
* The encoding is fixed to make the text/xml content type safer to use.
*
* @see JCR-1621
*/
public static final String ENCODING = "UTF-8";
/** The URI for xml namespaces */
private static final String XML = "http://www.w3.org/XML/1998/namespace";
/**
* The factory used to create serializing SAX transformers.
*/
private static final SAXTransformerFactory FACTORY =
// Note that the cast from below is strictly speaking only valid when
// the factory instance supports the SAXTransformerFactory.FEATURE
// feature. But since this class would be useless without this feature,
// it's no problem to fail with a ClassCastException here and prevent
// this class from even being loaded. AFAIK all common JAXP
// implementations do support this feature.
(SAXTransformerFactory) TransformerFactory.newInstance();
/**
* Flag that indicates whether we need to work around the issue of
* the serializer not automatically generating the required xmlns
* attributes for the namespaces used in the document.
*/
private static final boolean NEEDS_XMLNS_ATTRIBUTES =
needsXmlnsAttributes();
/**
* Probes the available XML serializer for xmlns support. Used to set
* the value of the {@link #NEEDS_XMLNS_ATTRIBUTES} flag.
*
* @return whether the XML serializer needs explicit xmlns attributes
*/
private static boolean needsXmlnsAttributes() {
try {
StringWriter writer = new StringWriter();
TransformerHandler probe = FACTORY.newTransformerHandler();
probe.setResult(new StreamResult(writer));
probe.startDocument();
probe.startPrefixMapping("p", "uri");
probe.startElement("uri", "e", "p:e", new AttributesImpl());
probe.endElement("uri", "e", "p:e");
probe.endPrefixMapping("p");
probe.endDocument();
return writer.toString().indexOf("xmlns") == -1;
} catch (Exception e) {
throw new UnsupportedOperationException("XML serialization fails");
}
}
/**
* Creates a serializing content handler that writes to the given stream.
*
* @param output serialization target
* @return serializing content handler
* @throws SAXException if the content handler could not be initialized
*/
public static DefaultHandler getSerializer(OutputStream output)
throws SAXException {
return getSerializer(new StreamResult(output));
}
/**
* Creates a serializing content handler that writes to the given writer.
*
* @param writer serialization target
* @return serializing content handler
* @throws SAXException if the content handler could not be initialized
*/
public static DefaultHandler getSerializer(Writer writer)
throws SAXException {
return getSerializer(new StreamResult(writer));
}
/**
* Creates a serializing content handler that writes to the given result.
*
* @param result serialization target
* @return serializing content handler
* @throws SAXException if the content handler could not be initialized
*/
public static DefaultHandler getSerializer(Result result)
throws SAXException {
try {
TransformerHandler handler = FACTORY.newTransformerHandler();
handler.setResult(result);
// Specify the output properties to avoid surprises especially in
// character encoding or the output method (might be html for some
// documents!)
Transformer transformer = handler.getTransformer();
transformer.setOutputProperty(OutputKeys.METHOD, "xml");
transformer.setOutputProperty(OutputKeys.ENCODING, ENCODING);
transformer.setOutputProperty(OutputKeys.INDENT, "no");
if (NEEDS_XMLNS_ATTRIBUTES) {
// The serializer does not output xmlns declarations,
// so we need to do it explicitly with this wrapper
return new SerializingContentHandler(handler);
} else {
return new DefaultContentHandler(handler);
}
} catch (TransformerConfigurationException e) {
throw new SAXException("Failed to initialize XML serializer", e);
}
}
/**
* The prefixes of startPrefixMapping() declarations for the coming element.
*/
private List prefixList = new ArrayList();
/**
* The URIs of startPrefixMapping() declarations for the coming element.
*/
private List uriList = new ArrayList();
/**
* Maps of URI<->prefix mappings. Used to work around a bug in the Xalan
* serializer.
*/
private Map uriToPrefixMap = new HashMap();
private Map prefixToUriMap = new HashMap();
/**
* True if there has been some startPrefixMapping() for the coming element.
*/
private boolean hasMappings = false;
/**
* Stack of the prefixes of explicitly generated prefix mapping calls
* per each element level. An entry is appended at the beginning of each
* {@link #startElement(String, String, String, Attributes)} call and
* removed at the end of each {@link #endElement(String, String, String)}
* call. By default the entry for each element is null to
* avoid losing performance, but whenever the code detects a new prefix
* mapping that needs to be registered, the null entry is
* replaced with a list of explicitly registered prefixes for that node.
* When that element is closed, the listed prefixes get unmapped.
*
* @see #checkPrefixMapping(String, String)
* @see JCR-1767
*/
private final List addedPrefixMappings = new ArrayList();
private SerializingContentHandler(ContentHandler handler) {
super(handler);
}
public void startDocument() throws SAXException {
// Cleanup
this.uriToPrefixMap.clear();
this.prefixToUriMap.clear();
clearMappings();
super.startDocument();
}
/**
* Track mappings to be able to add xmlns: attributes
* in startElement().
*/
public void startPrefixMapping(String prefix, String uri) throws SAXException {
// Store the mappings to reconstitute xmlns:attributes
// except prefixes starting with "xml": these are reserved
// VG: (uri != null) fixes NPE in startElement
if (uri != null && !prefix.startsWith("xml")) {
this.hasMappings = true;
this.prefixList.add(prefix);
this.uriList.add(uri);
// append the prefix colon now, in order to save concatenations later, but
// only for non-empty prefixes.
if (prefix.length() > 0) {
this.uriToPrefixMap.put(uri, prefix + ":");
} else {
this.uriToPrefixMap.put(uri, prefix);
}
this.prefixToUriMap.put(prefix, uri);
}
super.startPrefixMapping(prefix, uri);
}
/**
* Checks whether a prefix mapping already exists for the given namespace
* and generates the required {@link #startPrefixMapping(String, String)}
* call if the mapping is not found. By default the registered prefix
* is taken from the given qualified name, but a different prefix is
* automatically selected if that prefix is already used.
*
* @see JCR-1767
* @param uri namespace URI
* @param qname element name with the prefix, or null
* @throws SAXException if the prefix mapping can not be added
*/
private void checkPrefixMapping(String uri, String qname)
throws SAXException {
// Only add the prefix mapping if the URI is not already known
if (uri != null && uri.length() > 0 && !uri.startsWith("xml")
&& !uriToPrefixMap.containsKey(uri)) {
// Get the prefix
String prefix = "ns";
if (qname != null && qname.length() > 0) {
int colon = qname.indexOf(':');
if (colon != -1) {
prefix = qname.substring(0, colon);
}
}
// Make sure that the prefix is unique
String base = prefix;
for (int i = 2; prefixToUriMap.containsKey(prefix); i++) {
prefix = base + i;
}
int last = addedPrefixMappings.size() - 1;
List prefixes = (List) addedPrefixMappings.get(last);
if (prefixes == null) {
prefixes = new ArrayList();
addedPrefixMappings.set(last, prefixes);
}
prefixes.add(prefix);
startPrefixMapping(prefix, uri);
}
}
/**
* Ensure all namespace declarations are present as xmlns: attributes
* and add those needed before calling superclass. This is a workaround for a Xalan bug
* (at least in version 2.0.1) : org.apache.xalan.serialize.SerializerToXML
* ignores start/endPrefixMapping().
*/
public void startElement(
String eltUri, String eltLocalName, String eltQName, Attributes attrs)
throws SAXException {
// JCR-1767: Generate extra prefix mapping calls where needed
addedPrefixMappings.add(null);
checkPrefixMapping(eltUri, eltQName);
for (int i = 0; i < attrs.getLength(); i++) {
checkPrefixMapping(attrs.getURI(i), attrs.getQName(i));
}
// try to restore the qName. The map already contains the colon
if (null != eltUri && eltUri.length() != 0 && this.uriToPrefixMap.containsKey(eltUri)) {
eltQName = this.uriToPrefixMap.get(eltUri) + eltLocalName;
}
if (this.hasMappings) {
// Add xmlns* attributes where needed
// New Attributes if we have to add some.
AttributesImpl newAttrs = null;
int mappingCount = this.prefixList.size();
int attrCount = attrs.getLength();
for (int mapping = 0; mapping < mappingCount; mapping++) {
// Build infos for this namespace
String uri = (String) this.uriList.get(mapping);
String prefix = (String) this.prefixList.get(mapping);
String qName = prefix.equals("") ? "xmlns" : ("xmlns:" + prefix);
// Search for the corresponding xmlns* attribute
boolean found = false;
for (int attr = 0; attr < attrCount; attr++) {
if (qName.equals(attrs.getQName(attr))) {
// Check if mapping and attribute URI match
if (!uri.equals(attrs.getValue(attr))) {
throw new SAXException("URI in prefix mapping and attribute do not match");
}
found = true;
break;
}
}
if (!found) {
// Need to add this namespace
if (newAttrs == null) {
// Need to test if attrs is empty or we go into an infinite loop...
// Well know SAX bug which I spent 3 hours to remind of :-(
if (attrCount == 0) {
newAttrs = new AttributesImpl();
} else {
newAttrs = new AttributesImpl(attrs);
}
}
if (prefix.equals("")) {
newAttrs.addAttribute(XML, qName, qName, "CDATA", uri);
} else {
newAttrs.addAttribute(XML, prefix, qName, "CDATA", uri);
}
}
} // end for mapping
// Cleanup for the next element
clearMappings();
// Start element with new attributes, if any
super.startElement(eltUri, eltLocalName, eltQName, newAttrs == null ? attrs : newAttrs);
} else {
// Normal job
super.startElement(eltUri, eltLocalName, eltQName, attrs);
}
}
/**
* Receive notification of the end of an element.
* Try to restore the element qName.
*/
public void endElement(String eltUri, String eltLocalName, String eltQName) throws SAXException {
// try to restore the qName. The map already contains the colon
if (null != eltUri && eltUri.length() != 0 && this.uriToPrefixMap.containsKey(eltUri)) {
eltQName = this.uriToPrefixMap.get(eltUri) + eltLocalName;
}
super.endElement(eltUri, eltLocalName, eltQName);
// JCR-1767: Generate extra prefix un-mapping calls where needed
int last = addedPrefixMappings.size() - 1;
List prefixes = (List) addedPrefixMappings.remove(last);
if (prefixes != null) {
Iterator iterator = prefixes.iterator();
while (iterator.hasNext()) {
endPrefixMapping((String) iterator.next());
}
}
}
/**
* End the scope of a prefix-URI mapping:
* remove entry from mapping tables.
*/
public void endPrefixMapping(String prefix) throws SAXException {
// remove mappings for xalan-bug-workaround.
// Unfortunately, we're not passed the uri, but the prefix here,
// so we need to maintain maps in both directions.
if (this.prefixToUriMap.containsKey(prefix)) {
this.uriToPrefixMap.remove(this.prefixToUriMap.get(prefix));
this.prefixToUriMap.remove(prefix);
}
if (hasMappings) {
// most of the time, start/endPrefixMapping calls have an element event between them,
// which will clear the hasMapping flag and so this code will only be executed in the
// rather rare occasion when there are start/endPrefixMapping calls with no element
// event in between. If we wouldn't remove the items from the prefixList and uriList here,
// the namespace would be incorrectly declared on the next element following the
// endPrefixMapping call.
int pos = prefixList.lastIndexOf(prefix);
if (pos != -1) {
prefixList.remove(pos);
uriList.remove(pos);
}
}
super.endPrefixMapping(prefix);
}
public void endDocument() throws SAXException {
// Cleanup
this.uriToPrefixMap.clear();
this.prefixToUriMap.clear();
clearMappings();
super.endDocument();
}
private void clearMappings() {
this.hasMappings = false;
this.prefixList.clear();
this.uriList.clear();
}
}