Problems with servlet filters

Question

Hello,
I'm trying to implement filters for some of the examples presented in the j2ee tutorial. Thus, I've realized a very simple filter that works very well for the Converter example (mapped to the index.jsp URL). But this filter doesn't work with the Duke's Bank application and I don't understand why. I've tried to map this filter to the Dispatcher servlet and also to different URLs, the filter is actually executed, but the client gets no response from the server.
Here's the source code for my filter :
package com.sun.ebank.web.filters;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public final class MyFilter implements Filter {
private FilterConfig filterConfig = null;
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig = filterConfig;
public void destroy() {
this.filterConfig = null;
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
if (filterConfig == null) return;
HttpServletRequest hr = (HttpServletRequest)request;
System.out.println ("MyFilter : " + hr.getMethod () +      " URL=" + hr.getRequestURL () +          " QueryString={" + hr.getQueryString () + "}");
chain.doFilter(request, response);
public String toString() {
if (filterConfig ==null) return ("MyFilter()");
StringBuffer sb = new StringBuffer("MyFilter(");
sb.append(filterConfig);
sb.append(")");
return (sb.toString());
Can anybody help me?
Thanks,
B.F.

Answer 1

As you're not actually doing anything in this filter but a quick System.out.print, there doesn't appear to be a problem with the filter code.
What does your web.xml file look like?
Does your IDE allow you to trace through the filter to the next target in the chain? If so, where does the code die? If not, use System.out.print statements to determine how far into the code you get.
No response to the client usually means that the response didn't have any content set. You can verify this by checking the state of the response object after doFilter has been called; if the headers haven't been set then something crashed in a bad way.
Good luck!