Filter Example

Located in the tut-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 and Reading XML Streams for a more detailed discussion of StAX event parsing.

Building and Running the Filter Example Using NetBeans IDE

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

1. In NetBeans IDE, select File->Open Project.

2. In the Open Project dialog, navigate to the tut-install/javaeetutorial5/examples/stax/ directory.

3. Select the filter folder.

4. Select the Open as Main Project check box.

5. Click Open Project.

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.

Building and Running the Filter Example Using Ant

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

ant run-filter