displaying output from non-GUI Xerces applet

[Ron W Gilmour <gi...@lycos.com>]

Greetings!

I have a large XML-encoded bibliography (basically, repeated ENTRY 
elements, each with 4 children: AUTHOR, TITLE, SOURCE, ANNOTATION).  I 
would like to use Xerces to parse the XML in a non-displaying applet, then 
display the data as HTML in the browser.

I wrote a java application using Xerces/SAX which happily takes a string 
on the command line, finds all of the matching entries and returns them.  
I've spent a week trying to make this work in an applet with no luck.

The closest thing I can find to what I'm trying to write is the 
transformation applet that comes with Apache Xalan.  I notice that in the 
source code of that applet, the author (Scott Boag) creates a "trusted 
agent" thread to allow the applet to access foreign URL's.  Is this 
necessary even if the only file that the applet needs to access is in the 
same directory as the applet source?

The source code is pasted below.  The html page is just a 2 frame deal 
with an empty lower frame (for the results to appear in) and with the top 
frame containing a blank for the user to enter a search term and a button 
to start the search.  The following JavaScript is in the head of the upper 
frame: 

var searchString = "";
var results = "";

function clearFrames() {
	document.searchForm.searchBlank.value="";
	top.lower.document.open();
	top.lower.document.clear();
	top.lower.document.close();
}

function doSearch() {
    searchString = document.searchForm.searchBlank.value;
    results = document.SearchApplet.performSearch(searchString);
    top.lower.document.write("Results:<br>" + results);
}

The "clearFrames()" function is called "onLoad" from the body tag and 
the "doSearch()" function is called "onClick" from the search button:

<form name="searchForm" method="post">
<input type="text" name="searchBlank" maxlength="100" size="50">
<input type="button" name="searchButton" value="Search" 
onClick="doSearch();">
</form>
<applet name="SearchApplet" 
		code="SearchApplet.class" 
		archive="xerces.jar" 
		height="0" width="0">
<param name="uri" value="Royats.xml">
</applet>

When I load all of this (locally, using Internet Explorer 5.5), things 
look okay at first, but when I enter a search term and click the button, I 
get a javascript error that says "java.lang.NullPointerException".  
Nothing appears in the way of output, not even the "There is no output" 
message from the applet.

I apologize for the long post, but I'm getting a bit desperate.  Any help 
will be profoundly appreciated!

Sincerely,

Ron Gilmour
gilmr@lycos.com

import java.io.*;
import java.util.*;
import java.applet.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;
import org.apache.xerces.parsers.SAXParser;

public class SearchApplet extends Applet {
		
	public String results;
	public static String searchString;
	public String uri;

	public void init() {
    	uri = getParameter("uri");
	}

    public String performSearch(String searchString) {
    	
    	this.searchString = searchString;
    	
		ContentHandler contentHandler = new MyContentHandler();

		try {
	    	XMLReader parser = new SAXParser();
	    	parser.setContentHandler(contentHandler);
	    	parser.parse(uri);
		} catch (IOException e) {
	  	System.out.println("Error reading URI: " + e.getMessage());
		} catch (SAXException e) {
	    	System.out.println("Error parsing URI: " + e.getMessage());
		}
		results = MyContentHandler.getOutput();
		return results;
    }
    
}

// Class for reading and processing the XML data
	
class MyContentHandler implements ContentHandler {
    
	private Locator locator;
	private Vector entries;
	private String author;
	private String title;
    private String source;
    private String annotation;
    private CharArrayWriter contents;
    private Entry current;
    private String tempAuthor;
    private static String output;

   	public void setDocumentLocator(Locator locator) {
		this.locator = locator;
    }

    public void startDocument() throws SAXException {
		entries = new Vector();
		contents = new CharArrayWriter();
    }

   	public void startElement(String namespaceURI, 
		     String localName, String rawName, 
		     Attributes atts) throws SAXException {
			contents.reset();
    }

    public void characters(char[] ch, int start, int end) throws 
SAXException {
		contents.write(ch, start, end);
    }

    public void endElement (String namespaceURI, String localName, 
		    String rawName) throws SAXException {
		if (localName.equals("author")) {
	    	author = contents.toString();
		}
		else if (localName.equals("title")) {
	    	title = contents.toString();
		}
		else if (localName.equals("source")) {
	    	source = contents.toString();
		}
		else if (localName.equals("annotation")) {
	   		annotation = contents.toString();
		}
		else if (localName.equals("entry")) {
	    	entries.addElement(new Entry(author, title, source, 
annotation));
		}
    }

    public void endDocument() throws SAXException {
		for(int i=0; i<entries.size(); i++) {
	    	current = (Entry) entries.elementAt(i);
	    	tempAuthor = current.getAuthor().toUpperCase();
	    	if (tempAuthor.indexOf(SearchApplet.searchString) >= 0) {
			output += (current.getAuthor() + "<br>" + 
		   		current.getTitle() + "<br>" + 
		   	        current.getSource() + "<br>" + 
                                current.getAnnotation()+ "<br><br>");
	    	}
	}
    }

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

    public void startPrefixMapping(String prefix, String uri) {}

    public void endPrefixMapping(String prefix) {}

    public void ignorableWhitespace(char[] ch, int start, 
								
	int end) throws SAXException {}

    public void skippedEntity(String name) throws SAXException {}
    	
    public static String getOutput() {
    	if (output.length() > 0) {
    		return output;
    	} else {
    		return("There is no output!");
    	}
    }
}
    
    
// Class for holding Entry information
	
class Entry {
    private String author, title, source, annotation;

    // Constructor
    public Entry (String author, String title,
		  String source, String annotation) {
	this.author = author;
	this.title = title;
	this.source = source;
	this.annotation = annotation;
    }

    // Accessor methods
    public String getAuthor() { return author; }
    public String getTitle() { return title; }
    public String getSource() { return source; }
    public String getAnnotation() { return annotation; }
}

---
You are currently subscribed to java_xml as: gilmr@lycos.com
To unsubscribe send a blank email to leave-java_xml-542774O@p2p.wrox.com



--------- End Forwarded Message ---------



Get 250 color business cards for FREE!
http://businesscards.lycos.com/vp/fastpath/

---------------------------------------------------------------------
To unsubscribe, e-mail: xerces-j-user-unsubscribe@xml.apache.org
For additional commands, e-mail: xerces-j-user-help@xml.apache.org