Example Code






Example Code

This section steps through the example StAX code included in the Java EE 5 Tutorial bundle. All example directories used in this section are located in the <INSTALL>/javaeetutorial5/examples/stax/ directory.

The topics covered in this section are as follows:

  • Example code organization

  • Example XML document

  • Cursor example

  • Cursor-to-Event example

  • Event example

  • Filter example

  • Read-and-Write example

  • Writer example

Example Code Organization

The <INSTALL>/javaeetutorial5/examples/stax/ directory contains the six StAX example directories:

  • Cursor example: The cursor directory contains CursorParse.java, which illustrates how to use the XMLStreamReader (cursor) API to read an XML file.

  • Cursor-to-Event example: The cursor2event directory contains CursorApproachEventObject.java, which illustrates how an application can get information as an XMLEvent object when using cursor API.

  • Event example: The event directory contains EventParse.java, which illustrates how to use the XMLEventReader (event iterator) API to read an XML file.

  • Filter example: The filter directory contains MyStreamFilter.java, which illustrates how to use the StAX Stream Filter APIs. In this example, the filter accepts only StartElement and EndElement events, and filters out the remainder of the events.

  • Read-and-Write example: The readnwrite directory contains EventProducerConsumer.java, which illustrates how the StAX producer/consumer mechanism can be used to simultaneously read and write XML streams.

  • Writer example: The writer directory contains CursorWriter.java, which illustrates how to use XMLStreamWriter to write an XML file programatically.

All of the StAX examples except for the Writer example use an example XML document, BookCatalog.xml.

Example XML Document

The example XML document, BookCatalog.xml, used by most of the StAX example classes, is a simple book catalog based on the common BookCatalogue namespace. The contents of BookCatalog.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 Example

Located in the <INSTALL>/javaeetutorial5/examples/stax/cursor/ directory, CursorParse.java demonstrates using the StAX cursor API to read an XML document. In the Cursor example, 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 a 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 print the information about
                  // the particular event by calling the 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 staticString getEventTypeString(inteventType)
   {
     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;
   }

Building and Running the Cursor Example Using NetBeans 5.5

Follow these instructions to build and run the Cursor example on your Application Server instance using the NetBeans 5.5 IDE.

1.
In NetBeans 5.5, select FileOpen Project.

2.
In the Open Project dialog, navigate to the <INSTALL>/javaeetutorial5/examples/stax/ directory.

3.
Select the cursor folder.

4.
Select the Open as Main Project checkbox.

5.
Click Open Project Folder.

6.
In the Projects tab, right-click the cursor project and select Properties. The Project Properties dialog is displayed.

7.
Enter the following in the Arguments field:

-x 1 BookCatalog.xml

8.
Click OK.

9.
Right-click the cursor project and select Run Project.

Building and Running the Cursor Example Using Ant

To compile and run the Cursor example using Ant, in a terminal window, go to the <INSTALL>/javaeetutorial5/examples/stax/cursor/ directory and type the following:

   ant run-cursor

Cursor-to-Event Example

Located in the <INSTALL>/javaeetutorial5/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, while the event iterator API's XMLEventReader returns immutable and persistent event objects. XMLStreamReader is more efficient, but XMLEventReader is easier to use, because 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);
   }

Building and Running the Cursor-to-Event Example Using NetBeans 5.5

Follow these instructions to build and run the Cursor-to-Event example on your Application Server instance using the NetBeans 5.5 IDE.

1.
In NetBeans 5.5, select FileOpen Project.

2.
In the Open Project dialog, navigate to the <INSTALL>/javaeetutorial5/examples/stax/ directory.

3.
Select the cursor2event folder.

4.
Select the Open as Main Project checkbox.

5.
Click Open Project Folder.

6.
In the Projects tab, right-click the cursor2event project and select Properties. The Project Properties dialog is displayed.

7.
Enter the following in the Arguments field:

BookCatalog.xml

8.
Click OK.

9.
Right-click the cursor2event project and select Run Project.

Note how the Book events are returned as strings.

Building and Running the Cursor-to-Event Example Using Ant

To compile and run the Cursor-to-Event example using Ant, in a terminal window, go to the <INSTALL>/javaeetutorial5/examples/stax/cursor2event/ directory and type the following:

   ant run-cursor2event

Event Example

Located in the <INSTALL>/javaeetutorial5/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;
   }

Returning the Output

When you run the Event example, the EventParse 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.

Building and Running the Event Example Using NetBeans 5.5

Follow these instructions to build and run the Event example on your Application Server instance using the NetBeans 5.5 IDE.

1.
In NetBeans 5.5, select FileOpen Project.

2.
In the Open Project dialog, navigate to the <INSTALL>/javaeetutorial5/examples/stax/ directory.

3.
Select the event folder.

4.
Select the Open as Main Project checkbox.

5.
Click Open Project Folder.

6.
In the Projects tab, right-click the event project and select Properties. The Project Properties dialog is displayed.

7.
Enter the following in the Arguments field:

BookCatalog.xml

8.
Click OK.

9.
Right-click the event project and select Run Project.

Building and Running the Event Example Using Ant

To compile and run the Event example using Ant, in a terminal window, go to the <INSTALL>/javaeetutorial5/examples/stax/event/ directory and type the following:

   ant run-event

Filter Example

Located in the <INSTALL>/javaeetutorial5/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 class 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_REFERENCES,
     Boolean.TRUE);
   xmlif.setProperty(
     XMLInputFactory.IS_SUPPORTING_EXTERNAL_ENTITIES,
     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 example.

Filtering the Stream

The final step is to filter the stream:

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

Returning the Output

When you run the Filter example, the MyStreamFilter 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 Iterator API (page 596) and Reading XML Streams (page 606) for a more detailed discussion of StAX event parsing.

Building and Running the Filter Example Using NetBeans 5.5

Follow these instructions to build and run the Filter example on your Application Server instance using the NetBeans 5.5 IDE.

1.
In NetBeans 5.5, select FileOpen Project.

2.
In the Open Project dialog, navigate to the <INSTALL>/javaeetutorial5/examples/stax/ directory.

3.
Select the filter folder.

4.
Select the Open as Main Project checkbox.

5.
Click Open Project Folder.

6.
In the Projects tab, right-click the filter project and select Properties. The Project Properties dialog is displayed.

7.
Enter the following in the Arguments field:

-f BookCatalog.xml

8.
Click OK.

9.
Right-click the filter project and select Run Project.

Building and Running the Filter Example Using Ant

To compile and run the Filter example using Ant, in a terminal window, go to the <INSTALL>/javaeetutorial5/examples/stax/filter/ directory and type the following:

   ant run-filter

Read-and-Write Example

Located in the <INSTALL>/javaeetutorial5/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.

The Read-and-Write example shows how the StAX producer/consumer mechanism can be used to read and write simultaneously. This example also shows how a stream can be modified and how new events can be added dynamically and then written to a 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;
   }

Returning the Output

When you run the Read-and-Write example, the EventProducerConsumer class is compiled, and the XML stream is parsed as events and written back to STDOUT. The output is the contents of the BookCatalog.xml file described in Example XML Document (page 614).

Building and Running the Read-and-Write Example Using NetBeans 5.5

Follow these instructions to build and run the Read-and-Write example on your Application Server instance using the NetBeans 5.5 IDE.

1.
In NetBeans 5.5, select FileOpen Project.

2.
In the Open Project dialog, navigate to the <INSTALL>/javaeetutorial5/examples/stax/ directory.

3.
Select the readnwrite folder.

4.
Select the Open as Main Project checkbox.

5.
Click Open Project Folder.

6.
In the Projects tab, right-click the readnwrite project and select Properties. The Project Properties dialog is displayed.

7.
Enter the following in the Arguments field:

BookCatalog.xml

8.
Click OK.

9.
Right-click the readnwrite project and select Run Project.

Building and Running the Read-and-Write Example Using Ant

To compile and run the Read-and-Write example using Ant, in a terminal window, go to the <INSTALL>/javaeetutorial5/examples/stax/readnwrite/ directory and type the following:

   ant run-readnwrite

Writer Example

Located in the <INSTALL>/javaeetutorial5/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();

Returning the Output

When you run the Writer example, the CursorWriter class is compiled, and the XML stream is parsed as events and written to a file named dist/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>

In the actual dist/CursorWriter-Output file, this stream is written without any line breaks; the breaks have been added here to make the listing easier to read. In this example, as with the object stream in the Event example, the namespace prefix is added to both the opening and closing HTML tags. Adding this prefix is not required by the StAX specification, but it is good practice when the final scope of the output stream is not definitively known.

Building and Running the Writer Example Using NetBeans 5.5

Follow these instructions to build and run the Writer example on your Application Server instance using the NetBeans 5.5 IDE.

1.
In NetBeans 5.5, select FileOpen Project.

2.
In the Open Project dialog navigate to the <INSTALL>/javaeetutorial5/examples/stax/ directory.

3.
Select the writer folder.

4.
Select the Open as Main Project checkbox.

5.
Click Open Project Folder.

6.
In the Projects tab, right-click the writer project and select Properties. The Project Properties dialog is displayed.

7.
Enter the following in the Arguments field:

-f dist/CursorWriter-Output

8.
Click OK.

9.
Right-click the writer project and select Run Project.

Building and Running the Writer Example Using Ant

To compile and run the Writer example using Ant, in a terminal window, go to the <INSTALL>/javaeetutorial5/examples/stax/writer/ directory and type the following:

   ant run-writer



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