The getContent() method of the URL and URLConnection
classes will not load content handlers in packages identified
by the java.content.handler.pkgs property from the local
classpath in a stand-alone application. This is because it
uses the bootclasspath class loader instead of the normal
application class loader. This bug is present starting in JDK 1.2
and continuing through JDK 1.3b1 on both Solaris and Windows.
It is not present in JDK 1.1. It is the change in class loading
behavior made in Java 2 that broke content handlers.

Here's a sample program that demonstrates the problem.
The program connects to my web server and attempts to get some
tab separated content. However, it fails to use this content handler
and instead uses the default content handler that's available in the
bootclasspath.  

---------Cut Here----------
package com.macfaq.net.www.content.text;

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


public class tab_separated_values extends ContentHandler {

  public static void main(String[] args) {
   
    
    System.setProperty("java.content.handler.pkgs", "com.macfaq.net.www.content"); 
    
    try {
      URL u = new URL("http://metalab.unc.edu/javafaq/addresses.tab");
      Object o = u.getContent();
      // o should be a Vector if the content handler is found. Is it?
      if (o instanceof Vector) {
        System.out.println("Test succeeded. o is a " + o.getClass()); 
      }
      else {
        System.out.println("Test failed. o is a " + o.getClass());         
      }
      
    }
    catch (Exception e) {
      e.printStackTrace(); 
    }
    
    
  }
  
  public Object getContent(URLConnection uc) throws IOException {

    return new Vector(); 

  }

}
---------Cut Here---------

Here's typical output:

% java com.macfaq.net.www.content.text.tab_separated_values
Test failed. o is a class sun.net.www.MeteredStream

There are multiple workarounds. Installing a ContentHandlerFactory 
will allow the local content handlers to be loaded. So will using 
the oldjava interpreter instead of the java interpreter. Finally you 
can use the non-standard -Xbootclasspath command line option to add 
your content handlers to the bootclasspath instead of the regular classpath. 
For example,

D:\JAVA\JNP2\examples\16\bugtest>java -Xbootclasspath:.;D:\jdk1.3\jre\lib\rt.jar
 com.macfaq.net.www.content.text.tab_separated_values
Test succeeded. o is a class java.util.Vector