Sample Code

This section steps through the sample StAX code included in the J2EE 1.4 Tutorial bundle. All sample directories used in this section are located off the <javaee.tutorial.home>/examples/stax directory.

The topics covered in this section are as follows:

Sample Code Organization

There are seven StAX sample directories in <javaee.tutorial.home>/examples/stax:

Configuring Your Environment for Running the Samples

The instructions for configuring your environment are the same as those for running the other J2EE Tutorial samples. Specifically, to configure your environment for running the StAX examples, follow the steps below.

Note: If you are configuring the samples to run in a Microsoft Windows environment, use UNIX-style forward slashes (/) rather than Windows-style backslashes (\) to separate directory names when specifying paths in the steps below. For example, if your Application Server PE installation is in c:\Sun\AppServer, specify c:/Sun/AppServer instead.

  1. Set the following two properties in <javaee.tutorial.home>/examples/common/build.properties:
    • javaee.home to the directory in which SJSAS PE 9.0 is installed
    • javaee.tutorial.home to the directory in which the J2EE 1.4 Tutorial is installed.
  2. Specify the admin password used for your Application Server installation in <javaee.tutorial.home>/examples/common/admin-password.txt.
  3. You may also need to specify the path to the asant command in your PATH environment variable; for example, on UNIX/Linux:
    4.   export PATH=$PATH:/opt/SUNWappserver/bin/ 
 
    
or, on Windows:

    
  set PATH=%PATH%;c:\Sun\AppServer\bin 
 
    
asant is a script wrapper around the implementation of Ant bundled with the J2EE 1.4 Tutorial. Be sure to use this Ant implementation when running the tutorial samples rather than any other Ant implementation you may have installed on your system. Also be sure to use the asant wrapper rather than running Ant directly.
  4. Finally, note that the build.xml files in the various stax sample directories include classpath references to <javaee.home>/lib/javaee.jar and <javaee.home>/lib/appserv-ws.jar. You should not change these values, and if you create your own build.xml files, be sure to include these classpath references.

Running the Samples

The samples are run by means of the asant Ant wrapper and three build targets, defined in the <javaee.tutorial.home>/stax/samples/build.xml file. When you run any of the samples, the compiled class files are placed in a directory named ./build. This directory is created if it does not exist already.

Note: As mentioned above, be sure to use the implementation of Ant bundled with the J2EE Tutorial rather than any version of Ant you may already have installed on your system. Also be sure to use the asant wrapper script rather than running Ant directly.

There is a separate build.xml file in each of the stax sample directories except common, and each build.xml file provides the same three targets. Switch to the directory containing the sample you want to run, and then run the desired build.xml target from there.

The three Ant targets defined in each of the StAX build.xml files are:

For example, to run the cursor example: 

cd <javaee.tutorial.home>/examples/stax/cursor
asant build
asant run

Sample XML Document

The sample XML document, BookCatalogue.xml, used by most of the StAX sample classes is located in the <javaee.tutorial.home>/examples/stax/common/data directory, and is a simple book catalog based on the common BookCatalogue namespace. The contents of BookCatalogue.xml are listed below: 

<?xml version="1.0" encoding="UTF-8"?>
<BookCatalogue xmlns="http://www.publishing.org">
  <Book>
    <Title>Yogasana Vijnana: the Science of Yoga</Title>
    <author>Dhirendra Brahmachari</Author>
    <Date>1966</Date>
    <ISBN>81-40-34319-4</ISBN>
    <Publisher>Dhirendra Yoga Publications</Publisher>
    <Cost currency="INR">11.50</Cost>
  </Book>
  <Book>
    <Title>The First and Last Freedom</Title>
    <Author>J. Krishnamurti</Author>
    <Date>1954</Date>
    <ISBN>0-06-064831-7</ISBN>
    <Publisher>Harper &amp; Row</Publisher>
    <Cost currency="USD">2.95</Cost>
  </Book>
</BookCatalogue>

cursor Sample - CursorParse.java

Located in the <javaee.tutorial.home>/examples/stax/cursor directory, CursorParse.java demonstrates using the StAX cursor API to read an XML document. In this sample, the application instructs the parser to read the next event in the XML input stream by calling <code>next()</code>.

Note that <code>next()</code> just returns an integer constant corresponding to underlying event where the parser is positioned. The application needs to call the relevant function to get more information related to the underlying event.

You can imagine this approach as a virtual cursor moving across the XML input stream. There are various accessor methods which can be called when that virtual cursor is at particular event.

Stepping Through Events

In this example, the client application pulls the next event in the XML stream by calling the next() method on the parser; for example: 

try
  {
    for(int i =  0 ; i  < count ; i++)
      {
        //pass the file name.. all  relative  entity 
        //references will be resolved against  this as
        //base URI.
        XMLStreamReader xmlr  = 
xmlif.createXMLStreamReader(filename, new 
FileInputStream(filename));
        //when XMLStreamReader is created, it is positioned 
at START_DOCUMENT event.
        int eventType = xmlr.getEventType();
        //printEventType(eventType);
        printStartDocument(xmlr);
        //check if there are  more events  in  the input stream
        while(xmlr.hasNext())
          {
            eventType =  xmlr.next();
            //printEventType(eventType);
            //these functions  prints the information about 
the  particular event by calling relevant function
            printStartElement(xmlr);
            printEndElement(xmlr);
            printText(xmlr);
            printPIData(xmlr);
            printComment(xmlr);
          }
      }

Note that next() just returns an integer constant corresponding to the event underlying the current cursor location. The application calls the relevant function to get more information related to the underlying event. There are various accessor methods which can be called when the cursor is at particular event.

Returning String Representations

Because the next() method only returns integers corresponding to underlying event types, you typically need to map these integers to string representations of the events; for example: 

public final static  String getEventTypeString(int  eventType)
{
  switch  (eventType)
    {
        case XMLEvent.START_ELEMENT:
          return "START_ELEMENT";
        case XMLEvent.END_ELEMENT:
          return "END_ELEMENT";
        case XMLEvent.PROCESSING_INSTRUCTION:
          return "PROCESSING_INSTRUCTION";
        case XMLEvent.CHARACTERS:
          return "CHARACTERS";
        case XMLEvent.COMMENT:
          return "COMMENT";
        case XMLEvent.START_DOCUMENT:
          return "START_DOCUMENT";
        case XMLEvent.END_DOCUMENT:
          return "END_DOCUMENT";
        case XMLEvent.ENTITY_REFERENCE:
          return "ENTITY_REFERENCE";
        case XMLEvent.ATTRIBUTE:
          return "ATTRIBUTE";
        case XMLEvent.DTD:
          return "DTD";
        case XMLEvent.CDATA:
          return "CDATA";
        case XMLEvent.SPACE:
          return "SPACE";
    }
  return  "UNKNOWN_EVENT_TYPE ,   "+ eventType;
}

Running the Sample

When you run the CursorParse sample, the class is compiled, and the XML stream is parsed and returned to STDOUT.

cursor2event Sample - CursorApproachEventObject.java

Located in the <javaee.tutorial.home>/examples/stax/cursor2event directory, CursorApproachEventObject.java demonstrates how to get information returned by an XMLEvent object even when using the cursor API.

The idea here is that the cursor API's XMLStreamReader returns integer constants corresponding to particular events, where as the event iterator API's XMLEventReader returns immutable and persistent event objects. XMLStreamReader is more efficient, but XMLEventReader is easier to use, as all the information related to a particular event is encapsulated in a returned XMLEvent object. However, the disadvantage of event approach is the extra overhead of creating objects for every event, which consumes both time and memory.

With this mind, XMLEventAllocator can be used to get event information as an XMLEvent object, even when using the cursor API.

Instantiating an XMLEventAllocator

The first step is to create a new XMLInputFactory and instantiate an XMLEventAllocator: 

XMLInputFactory xmlif = XMLInputFactory.newInstance();
System.out.println("FACTORY: " + xmlif);
xmlif.setEventAllocator(new XMLEventAllocatorImpl());
allocator = xmlif.getEventAllocator();
XMLStreamReader xmlr = xmlif.createXMLStreamReader(filename, 
new FileInputStream(filename));

Creating an Event Iterator

The next step is to create an event iterator: 

int eventType = xmlr.getEventType();
while(xmlr.hasNext()){
  eventType = xmlr.next();
  //Get all "Book" elements as XMLEvent object
  if(eventType == XMLStreamConstants.START_ELEMENT && 
xmlr.getLocalName().equals("Book")){
    //get immutable XMLEvent
    StartElement event = getXMLEvent(xmlr).asStartElement();
    System.out.println("EVENT: " + event.toString());
  }
}

Creating the Allocator Method

The final step is to create the XMLEventAllocator method: 

private static XMLEvent getXMLEvent(XMLStreamReader reader) 
throws XMLStreamException{
  return allocator.allocate(reader);
}

Running the Sample

When you run the CursorApproachEventObject sample, the class is compiled, and the XML stream is parsed and returned to STDOUT. Note how the Book events are returned as strings.

event Sample - EventParse.java

Located in the <javaee.tutorial.home>/examples/stax/event directory, EventParse.java demonstrates how to use the StAX event API to read an XML document.

Creating an Input Factory

The first step is to create a new instance of XMLInputFactory: 

XMLInputFactory factory = XMLInputFactory.newInstance();
System.out.println("FACTORY: " + factory);

Creating an Event Reader

The next step is to create an instance of XMLEventReader: 

XMLEventReader r = factory.createXMLEventReader(filename, new 
FileInputStream(filename));

Creating an Event Iterator

The third step is to create an event iterator: 

XMLEventReader r = factory.createXMLEventReader(filename, new 
FileInputStream(filename));
while(r.hasNext()) {
  XMLEvent e = r.nextEvent();
  System.out.println(e.toString());
}

Getting the Event Stream

The final step is to get the underlying event stream: 

public final static String getEventTypeString(int eventType)
{
  switch (eventType)
    {
      case XMLEvent.START_ELEMENT:
        return "START_ELEMENT";
      case XMLEvent.END_ELEMENT:
        return "END_ELEMENT";
      case XMLEvent.PROCESSING_INSTRUCTION:
        return "PROCESSING_INSTRUCTION";
      case XMLEvent.CHARACTERS:
        return "CHARACTERS";
      case XMLEvent.COMMENT:
        return "COMMENT";
      case XMLEvent.START_DOCUMENT:
        return "START_DOCUMENT";
      case XMLEvent.END_DOCUMENT:
        return "END_DOCUMENT";
      case XMLEvent.ENTITY_REFERENCE:
        return "ENTITY_REFERENCE";
      case XMLEvent.ATTRIBUTE:
        return "ATTRIBUTE";
      case XMLEvent.DTD:
        return "DTD";
      case XMLEvent.CDATA:
        return "CDATA";
      case XMLEvent.SPACE:
        return "SPACE";
    }
  return "UNKNOWN_EVENT_TYPE " + "," + eventType;
}

Running the Sample

When you run the EventParse sample, the class is compiled, and the XML stream is parsed as events and returned to STDOUT. For example, an instance of the Author element is returned as: 

<['http://www.publishing.org']::Author>
Dhirendra Brahmachari
</['http://www.publishing.org']::Author>

Note in this example that the event comprises an opening and closing tag, both of which include the namespace. The content of the element is returned as a string within the tags.

Similarly, an instance of the Cost element is returned as: 

<['http://www.publishing.org']::Cost currency='INR'>
11.50
</['http://www.publishing.org']::Cost>

In this case, the currency attribute and value are returned in the opening tag for the event.

See earlier in this chapter, in the "Iterator API" and "Reading XML Streams" sections, for a more detailed discussion of StAX event parsing.

filter Sample - MyStreamFilter.java

Located in the <javaee.tutorial.home>/examples/stax/filter directory, MyStreamFilter.java demonstrates how to use the StAX stream filter API to filter out events not needed by your application. In this example, the parser filters out all events except StartElement and EndElement.

Implementing the StreamFilter Class

The MyStreamFilter implements javax.xml.stream.StreamFilter: 

public class MyStreamFilter implements 
javax.xml.stream.StreamFilter{

Creating an Input Factory

The next step is to create an instance of XMLInputFactory. In this case, various properties are also set on the factory: 

XMLInputFactory xmlif = null ;
try{
xmlif = XMLInputFactory.newInstance();
xmlif.setProperty(XMLInputFactory.IS_REPLACING_ENTITY_REFERENC
ES,Boolean.TRUE);
xmlif.setProperty(XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTIT
IES,Boolean.FALSE);
xmlif.setProperty(XMLInputFactory.IS_NAMESPACE_AWARE , 
Boolean.TRUE);
xmlif.setProperty(XMLInputFactory.IS_COALESCING , 
Boolean.TRUE);
}catch(Exception ex){
  ex.printStackTrace();
}
System.out.println("FACTORY: " + xmlif);
System.out.println("filename = "+ filename);

Creating the Filter

The next step is to instantiate a file input stream and create the stream filter: 

FileInputStream fis = new FileInputStream(filename);
        
XMLStreamReader xmlr = 
xmlif.createFilteredReader(xmlif.createXMLStreamReader(fis), 
new MyStreamFilter());

int eventType = xmlr.getEventType();
printEventType(eventType);
while(xmlr.hasNext()){
  eventType = xmlr.next();
  printEventType(eventType);
  printName(xmlr,eventType);
  printText(xmlr);
  if(xmlr.isStartElement()){
    printAttributes(xmlr);
  }
  printPIData(xmlr);
  System.out.println("-----------------------------");
}

Capturing the Event Stream

The next step is to capture the event stream. This is done in basically the same way as in the event Sample - EventParse.java sample.

Filtering the Stream

The final step is the filter the stream: 

public boolean accept(XMLStreamReader reader) {
  if(!reader.isStartElement() && !reader.isEndElement())
    return false;
  else
    return true;
}

Running the Sample

When you run the MyStreamFilter sample, the class is compiled, and the XML stream is parsed as events and returned to STDOUT. For example an Author event is returned as follows: 

EVENT TYPE(1):START_ELEMENT
HAS NAME: Author
HAS NO TEXT
HAS NO ATTRIBUTES
-----------------------------
EVENT TYPE(2):END_ELEMENT
HAS NAME: Author
HAS NO TEXT
-----------------------------

Similarly, a Cost event is returned as follows: 

EVENT TYPE(1):START_ELEMENT
HAS NAME: Cost
HAS NO TEXT

HAS ATTRIBUTES: 
ATTRIBUTE-PREFIX: 
ATTRIBUTE-NAMESP: null
ATTRIBUTE-NAME:   currency
ATTRIBUTE-VALUE: USD
ATTRIBUTE-TYPE:  CDATA

-----------------------------
EVENT TYPE(2):END_ELEMENT
HAS NAME: Cost
HAS NO TEXT
-----------------------------

See earlier in this chapter, in the "Iterator API" and "Reading XML Streams" sections, for a more detailed discussion of StAX event parsing.

readnwrite Sample - EventProducerConsumer.java

Located in the <javaee.tutorial.home>/examples/stax/readnwrite directory, EventProducerConsumer.java demonstrates how to use a StAX parser simultaneously as both a producer and a consumer.

The StAX XMLEventWriter API extends from the XMLEventConsumer interface, and is referred to as an event consumer. By contrast, XMLEventReader is an event producer. StAX supports simultaneous reading and writing, such that it is possible to read from one XML stream sequentially and simultaneously write to another stream.

This sample shows how the StAX producer/consumer mechanism can be used to read and write simultaneously. This sample also shows how a stream can be modified, and new events can be added dynamically and then written to different stream.

Creating an Event Producer/Consumer

The first step is to instantiate an event factory and then create an instance of an event producer/consumer: 

XMLEventFactory m_eventFactory=XMLEventFactory.newInstance();
public EventProducerConsumer() {
}
.
.
.
try{
  EventProducerConsumer ms = new EventProducerConsumer();
  
  XMLEventReader reader = 
XMLInputFactory.newInstance().createXMLEventReader(new 
java.io.FileInputStream(args[0]));
  XMLEventWriter writer = 
XMLOutputFactory.newInstance().createXMLEventWriter(System.out
);

Creating an Iterator

The next step is to create an iterator to parse the stream: 

while(reader.hasNext())
  {
    XMLEvent event = (XMLEvent)reader.next();
    if(event.getEventType() == event.CHARACTERS)
      {
        
writer.add(ms.getNewCharactersEvent(event.asCharacters()));
      }
    else
      {
        writer.add(event);
      }
  }
writer.flush();

Creating a Writer

The final step is to create a stream writer in the form of a new Character event: 

Characters getNewCharactersEvent(Characters event){
  if(event.getData().equalsIgnoreCase("Name1")){
    return 
m_eventFactory.createCharacters(Calendar.getInstance().getTime
().toString());

  }
  //else return the same event
  else return event;
}

Running the Sample

When you run the EventProducerConsumer sample, the class is compiled, and the XML stream is parsed as events and written back to STDOUT: 

<?xml version="1.0" encoding="UTF-8"?>
<BookCatalogue xmlns="http://www.publishing.org">
  <Book>
    <Title>Yogasana Vijnana: the Science of Yoga</Title>
    <Author>Dhirendra Brahmachari</Author>
    <Date>1966</Date>
    <ISBN>81-40-34319-4</ISBN>
    <Publisher>Dhirendra Yoga Publications</Publisher>
    <Cost currency="INR">11.50</Cost>
  </Book>

  <Book>
    <Title>The First and Last Freedom</Title>
    <Author>J. Krishnamurti</Author>
    <Date>1954</Date>
    <ISBN>0-06-064831-7</ISBN>
    <Publisher>Harper &amp; Row</Publisher>
    <Cost currency="USD">2.95</Cost>
  </Book>
</BookCatalogue>

writer Sample - CursorWriter.java

Located in the <javaee.tutorial.home>/examples/stax/writer directory, CursorWriter.java demonstrates how to use the StAX cursor API to write an XML stream.

Creating the Output Factory

The first step is to create an instance of XMLOutputFactory: 

XMLOutputFactory xof =  XMLOutputFactory.newInstance();

Creating a Stream Writer

The next step is to create an instance of XMLStreamWriter: 

XMLStreamWriter xtw = null;

Writing the Stream

The final step is to write the XML stream. Note that the stream is flushed and closed after the final EndDocument is written: 

xtw = xof.createXMLStreamWriter(new FileWriter(fileName));
xtw.writeComment("all elements here are explicitly in the HTML 
namespace");
xtw.writeStartDocument("utf-8","1.0");
xtw.setPrefix("html", "http://www.w3.org/TR/REC-html40");
xtw.writeStartElement("http://www.w3.org/TR/REC-
html40","html");
xtw.writeNamespace("html", "http://www.w3.org/TR/REC-html40");
xtw.writeStartElement("http://www.w3.org/TR/REC-
html40","head");
xtw.writeStartElement("http://www.w3.org/TR/REC-
html40","title");
xtw.writeCharacters("Frobnostication");
xtw.writeEndElement();
xtw.writeEndElement();
xtw.writeStartElement("http://www.w3.org/TR/REC-
html40","body");
xtw.writeStartElement("http://www.w3.org/TR/REC-html40","p");
xtw.writeCharacters("Moved to");
xtw.writeStartElement("http://www.w3.org/TR/REC-html40","a");
xtw.writeAttribute("href","http://frob.com");
xtw.writeCharacters("here");
xtw.writeEndElement();
xtw.writeEndElement();
xtw.writeEndElement();
xtw.writeEndElement();
xtw.writeEndDocument();
xtw.flush();
xtw.close();

Running the Sample

When you run the CursorWriter sample, the class is compiled, and the XML stream is parsed as events and written to a file named CursorWriter-Output: 

<!--all elements here are explicitly in the HTML namespace-->
<?xml version="1.0" encoding="utf-8"?>
<html:html xmlns:html="http://www.w3.org/TR/REC-html40">
<html:head>
<html:title>Frobnostication</html:title></html:head>
<html:body>
<html:p>Moved to <html:a href="http://frob.com">here</html:a>
</html:p>
</html:body>
</html:html>

Note that in the actual CursorWriter-Output file, this stream is written without any linebreaks; the breaks have been added here to make the listing easier to read. In this example, as with the object stream in the event Sample - EventParse.java sample, the namespace prefix is added to both the opening and closing HTML tags. This is not required by the StAX specification, but it is good practice when the final scope of the output stream is not definitively known.