Processing Xml With Java - A Guide To Sax, Dom, Jdom, Jaxp, And Trax

Receiving Processing Instructions

Each processing instruction that the parser reads is passed to the processingInstruction() method in one invocation. This includes processing instructions that occur before and after the root element. The target is given as the first argument and the data as the second argument.

public void processingInstruction (String target, String data)
 throws SAXException

Although many processing instructions such as xml-stylesheet use a pseudo-attribute format, this depends on the semantics defined for the particular target. The processingInstruction() method does not distinguish between processing instructions like xml-stylesheet that use pseudo-attributes and processing instructions like php that don't. The data of both kinds is passed to the processingInstruction() method as a single String. If you want to split that string into attributes and values, you have to write the code to do that yourself. SAX doesn't do it for you.

public void processingInstruction(String target, 
 String data) {

  if (target.equals("xml-stylesheet")) {
    ProcessingInstruction xml-stylesheet
     = new ProcessingInstruction(target, data);
    String href = xml-stylesheet.getValue("href");
  }

}

Example 6.11 demonstrates with a straightforward program to list the targets and data of all the processing instructions found in a document. Of course the real purpose of processing instructions is to pass their data to a separate program somehow identified by the target.

Example 6.11 A ContentHandler That Prints Processing Instruction Targets and Data on System.out

import org.xml.sax.*;
import org.xml.sax.helpers.XMLReaderFactory;

public class ProcessingInstructionLister extends DefaultHandler {


  public void processingInstruction(String target, String data) {

    System.out.println("Processing Instruction:");
    System.out.println("  target: " + target);
    System.out.println("  data:   " + data);
    System.out.println();

  }


  public static void main(String[] args) {

    try {
      XMLReader parser = XMLReaderFactory.createXMLReader(
        "org.apache.xerces.parsers.SAXParser"
      );
      ContentHandler handler = new ProcessingInstructionLister();
      parser.setContentHandler(handler);
      for (int i = 0; i < args.length; i++) {
        parser.parse(args[i]);
      }
    }
    catch (Exception e) {
      System.err.println(e);
    }
  }

}

Following is the output from running this program over styled_order.xml from Chapter 1. This document contains a single xml-stylesheet processing instruction. Note especially that the XML declaration is not considered to be a processing instruction and is not reported.

C:\XMLJAVA>java ProcessingInstructionLister styled_order.xml 
Processing Instruction:
  target: xml-stylesheet
  data:   type="text/css" href="order.css"