File: faq-sax.xml

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<?xml version='1.0' encoding='UTF-8'?>
<!--
 * 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.
-->
<!DOCTYPE faqs SYSTEM 'dtd/faqs.dtd'>
<faqs title='Programming with SAX'>

 <faq title="Creating a SAX Parser">
  <q>How do I create a SAX parser?</q>
  <a>
   <p>
    You can create a SAX parser by using the Java APIs for
    XML Processing (JAXP). The following source code shows
    how:
   </p>
   <source>import java.io.IOException; 
import javax.xml.parsers.FactoryConfigurationError;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

  ...

String xmlFile = &quot;file:///&parserdir;/data/personal.xml&quot;; 
try {
    SAXParserFactory factory = SAXParserFactory.newInstance();
    factory.setNamespaceAware(true);
    SAXParser parser = factory.newSAXParser();
    DefaultHandler handler = /* custom handler class */;
    parser.parse(xmlFile, handler);
} 
catch (FactoryConfigurationError e) {
    // unable to get a document builder factory
} 
catch (ParserConfigurationException e) {
    // parser was unable to be configured
catch (SAXException e) {
    // parsing error
} 
catch (IOException e) {
    // i/o error
}</source>
  </a>
 </faq>

  <faq title='Incomplete character data is received via SAX'>
  <q>Why does the SAX parser lose some character data or why is the data split 
  into several chunks?</q>
  <a>
  <p>If you read the <jump href='http://www.saxproject.org/apidoc/org/xml/sax/ContentHandler.html#characters(char[],%20int,%20int)'>SAX</jump> 
  documentation, you will find that SAX may deliver contiguous text as multiple calls to 
<code>characters</code>, for reasons having to do with parser efficiency and input 
buffering. It is the programmer's responsibility to deal with that 
appropriately, e.g. by accumulating text until the next non-characters 
event.
 </p>
 <p>
   Xerces will split calls to <code>characters</code> at the end of an internal buffer,
   at a new line and also at a few other boundaries. You can never rely on contiguous
   text to be passed in a single characters callback.
 </p>
  </a>
  </faq>
  
  <faq title='Ignorable Whitespace and XML Schemas'>
    <q>Why doesn't the SAX parser report ignorable whitespace for XML Schemas?</q>
    <a>
      <p>SAX is very clear that ignorableWhitespace is only called for
         <jump href="http://www.w3.org/TR/2006/REC-xml-20060816/#sec-white-space">
         element content whitespace</jump>, which is defined in the context of a DTD.
         The result of schema validation is the Post-Schema-Validation Infoset (PSVI). 
         Schema processors augment the base Infoset by adding new properties to 
         element and attribute information items, but not character information items.
         Schemas do not change whether a character is element content whitespace.
      </p>
    </a>
  </faq>
  
  <faq title="Attributes and ContentHandler.startElement">
    <q>Why is the Attributes parameter passed to startElement always a 
    reference to the same object?</q>
    <a>
      <p>Outside the scope of <code>startElement</code>, the value of the 
         <code>Attributes</code> parameter is undefined. For each instance of Xerces'
         SAX parser, there exists only one <code>Attributes</code> instance which 
         is reused for every new set of attributes. Before each 
         <code>startElement</code> callback, the previous values in this object
         will be overwritten. This is done for performance reasons in order
         to reduce object creation. To persist a set of attributes
         beyond <code>startElement</code> the object should be cloned, for
         instance by using <code>org.xml.sax.helpers.AttributesImpl</code>.
      </p>
    </a>
  </faq>
  
  <faq title="Namespace of xmlns attributes">
    <q>Why does the SAX parser report that xmlns attributes have no namespace?</q>
    <a>
       <p>An erratum for the Namespaces in XML Recommendation put namespace declaration 
          attributes in the namespace "http://www.w3.org/2000/xmlns/". By default, 
          SAX2 (SAX 2.0.2) follows the original Namespaces in XML Recommendation, so 
          conforming parsers must report that these attributes have no namespace. To
          configure the parser to report a namespace for such attributes, turn on
          the <link idref='features' anchor='xmlns-uris'>xmlns-uris</link> feature.
       </p>
       <p>When using Xerces 2.6.2 (or prior) or other parser implementations
          that do not support this feature, your code must handle this discrepancy
          when interacting with APIs such as DOM and applications which expect a namespace 
          for xmlns attributes.
       </p>
    </a>
  </faq>

  <faq title="Encodings and XML Version via SAX">
    <q>Is there any way I can determine what encoding an entity was
    written in, or what XML version the document conformed to, if I'm
    using SAX?</q>
    <a>
        <p>Yes. As of SAX 2.0.2 encoding and version information is made
        available through the <code>org.xml.sax.ext.Locator2</code>
        interface. In Xerces, instances of the SAX <code>Locator</code> interface
        passed to a <code>setDocumentLocator</code> call will also implement
        the <code>Locator2</code> interface. You can determine the encoding
        and XML version of the entity currently being parsed by calling the
        <code>getEncoding()</code> and <code>getXMLVersion()</code> methods.
        </p>
    </a>
  </faq>
  

</faqs>