saxlocalnamecount.java

Read web RSS Feeds to break it into simple tags elements

// JAXP packages
import javax.xml.parsers.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;

import java.util.*;
import java.io.*;

/**
 * Program to count the number of elements using only the localName
 * component of the element, in an XML document.  Namespace names are
 * ignored for simplicity.  This example also shows one way to turn on
 * validation and how to use a SAX ErrorHandler.
 *
 * Notes: DefaultHandler is a SAX helper class that implements the SAX
 * ContentHandler interface by providing no-op methods.  This class
 * overrides some of the methods by extending DefaultHandler.  This program
 * turns on namespace processing and uses SAX2 interfaces to process XML
 * documents which may or may not be using namespaces.
 *
 * Update 2002-04-18: Added code that shows how to use JAXP 1.2 features to
 * support W3C XML Schema validation.  See the JAXP 1.2 maintenance review
 * specification for more information on these features.
 *
 */
public class SAXLocalNameCount extends DefaultHandler {

    /** A Hashtable with tag names as keys and Integers as values */
    private Hashtable tags;

    // Parser calls this once at the beginning of a document
    public void startDocument() throws SAXException {
        tags = new Hashtable();
    }

    // Parser calls this for each element in a document
    public void startElement(String namespaceURI, String localName,
                             String qName, Attributes atts)
	throws SAXException
    {
        String key = localName;
        Object value = tags.get(key);
        if (value == null) {
            // Add a new entry
            tags.put(key, new Integer(1));
        } else {
            // Get the current count and increment it
            int count = ((Integer)value).intValue();
            count++;
            tags.put(key, new Integer(count));
        }
    }

    // Parser calls this once after parsing a document
    public void endDocument() throws SAXException {
        Enumeration e = tags.keys();
        while (e.hasMoreElements()) {
            String tag = (String)e.nextElement();
            int count = ((Integer)tags.get(tag)).intValue();
            System.out.println("Local Name \"" + tag + "\" occurs " + count
                               + " times");
        }
    }

    /**
     * Convert from a filename to a file URL.
     */
    private static String convertToFileURL(String filename) {
        // On JDK 1.2 and later, simplify this to:
        // "path = file.toURL().toString()".
        String path = new File(filename).getAbsolutePath();
        if (File.separatorChar != '/') {
            path = path.replace(File.separatorChar, '/');
        }
        if (!path.startsWith("/")) {
            path = "/" + path;
        }
        return "file:" + path;
    }

    private static void usage() {
        System.err.println("Usage: SAXLocalNameCount [-options] <file.xml>");
        System.err.println("       -dtd = DTD validation");
        System.err.println("       -usage or -help = this message");
        System.exit(1);
    }

    static public void main(String[] args) throws Exception {
        String filename = null;
        boolean dtdValidate = false;
        String schemaSource = null;

        // Parse arguments
        for (int i = 0; i < args.length; i++) {
            if (args[i].equals("-dtd")) {
                dtdValidate = true;
            } else if (args[i].equals("-usage")) {
                usage();
            } else if (args[i].equals("-help")) {
                usage();
            } else {
                filename = args[i];

                // Must be last arg
                if (i != args.length - 1) {
                    usage();
                }
            }
        }
        if (filename == null) {
            usage();
        }

        // There are several ways to parse a document using SAX and JAXP.
        // We show one approach here.  The first step is to bootstrap a
        // parser.  There are two ways: one is to use only the SAX API, the
        // other is to use the JAXP utility classes in the
        // javax.xml.parsers package.  We use the second approach here
        // because at the time of this writing it probably is the most
        // portable solution for a JAXP compatible parser.  After
        // bootstrapping a parser/XMLReader, there are several ways to
        // begin a parse.  In this example, we use the SAX API.

        // Create a JAXP SAXParserFactory and configure it
        SAXParserFactory spf = SAXParserFactory.newInstance();

        // Set namespaceAware to true to get a parser that corresponds to
        // the default SAX2 namespace feature setting.  This is necessary
        // because the default value from JAXP 1.0 was defined to be false.
        spf.setNamespaceAware(true);

        // Validation part 1: set whether validation is on
        spf.setValidating(dtdValidate);

        // Create a JAXP SAXParser
        SAXParser saxParser = spf.newSAXParser();



        // Get the encapsulated SAX XMLReader
        XMLReader xmlReader = saxParser.getXMLReader();

        // Set the ContentHandler of the XMLReader
        xmlReader.setContentHandler(new SAXLocalNameCount());

        // Set an ErrorHandler before parsing
        xmlReader.setErrorHandler(new MyErrorHandler(System.err));

        // Tell the XMLReader to parse the XML document
        xmlReader.parse(convertToFileURL(filename));
    }

    // Error handler to report errors and warnings
    private static class MyErrorHandler implements ErrorHandler {
        /** Error handler output goes here */
        private PrintStream out;

        MyErrorHandler(PrintStream out) {
            this.out = out;
        }

        /**
         * Returns a string describing parse exception details
         */
        private String getParseExceptionInfo(SAXParseException spe) {
            String systemId = spe.getSystemId();
            if (systemId == null) {
                systemId = "null";
            }
            String info = "URI=" + systemId +
                " Line=" + spe.getLineNumber() +
                ": " + spe.getMessage();
            return info;
        }

        // The following methods are standard SAX ErrorHandler methods.
        // See SAX documentation for more info.

        public void warning(SAXParseException spe) throws SAXException {
            out.println("Warning: " + getParseExceptionInfo(spe));
        }
        
        public void error(SAXParseException spe) throws SAXException {
            String message = "Error: " + getParseExceptionInfo(spe);
            throw new SAXException(message);
        }

        public void fatalError(SAXParseException spe) throws SAXException {
            String message = "Fatal Error: " + getParseExceptionInfo(spe);
            throw new SAXException(message);
        }
    }
}