Getting at Response data in a servlet filter??

Question

Hi,
I'm hoping an expert would point me in the right direction.
I'm writing a filter that'll act like a proxy. It'll need to inspect the response data coming back from the server, and also forward the response data back to the browser.
As a first step, I've written a TestFilter that'll print the response data. When I go to print the response data in the TestFilter, it doesn't print anything! However, if I get print the contentLength of the response, it shows up as 3000!
I know response isn't null, as the page gets displayed on to the browser that makes the request.
How do I get at the response data?
Thanks,
--Sridhar
Here is the sample filter -
// HeaderFilter.java
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
public class HeaderFilter extends GenericFilter {
public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
throws java.io.IOException, javax.servlet.ServletException {
ServletContext context = filterConfig.getServletContext();
HttpServletRequest request = (HttpServletRequest)req;
CharResponseWrapper wrapper = new CharResponseWrapper((HttpServletResponse)resp);
chain.doFilter(request, wrapper);
System.out.println("******RESPONSE INFO******");
System.out.println("The response is " + wrapper.toString());
class CharResponseWrapper extends HttpServletResponseWrapper {
private CharArrayWriter output;
public String toString() {
return output.toString();
public CharResponseWrapper(HttpServletResponse response){
super(response);
output = new CharArrayWriter();
public PrintWriter getWriter(){
return new PrintWriter(output);
// Here is the output...
******RESPONSE INFO******
The response is

Answer 1

I'm still baffled!!
Here is the output I see in the console when I expect to see a lot more. This is the behaviour under both JRun & Weblogic. It makes me think that I'm missing something subtle!
Could the experts point me in the right direction? This is really stumping me & the deadlines are looming large :(
Output is -
*** TEST FILTER ***
************** RESPONSE DATA ***********
[B@2fb7ef
Here is the test filter implementation -
// TestFilter.java
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.OutputStream;
public class TestFilter extends GenericFilter {
public void doFilter(final ServletRequest request, final ServletResponse response, FilterChain chain) throws IOException, ServletException
System.out.println("*** TEST FILTER ***");
OutputStream out = response.getOutputStream();
TestResponseWrapper wrapper = new TestResponseWrapper((HttpServletResponse) response);
chain.doFilter(request, wrapper);
System.out.println("************** RESPONSE DATA ***********");
System.out.println(wrapper.getData());
out.write(wrapper.getData());
out.close();
// TestResponseWrapper.java
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import java.io.ByteArrayOutputStream;
import java.io.PrintWriter;
public class TestResponseWrapper extends HttpServletResponseWrapper{   
private ByteArrayOutputStream output;
private int contentLength;
private String contentType;
public TestResponseWrapper(HttpServletResponse response) {       
super(response);
output = new ByteArrayOutputStream();
public ServletOutputStream getOutputStream() {       
return new FilterServletOutputStream(output);
public byte[] getData() {
return output.toByteArray();
public PrintWriter getWriter() {   
return new PrintWriter(getOutputStream(), true);
public void setContentType(String type) {       
this.contentType = type;
super.setContentType(type);
public String getContentType() {       
return this.contentType;
public int getContentLength() {    
return contentLength;
public void setContentLength(int length) {       
this.contentLength=length;
super.setContentLength(length);
// FilterOutputStream.java
import javax.servlet.ServletOutputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
public class FilterServletOutputStream extends ServletOutputStream {
private DataOutputStream stream;
public FilterServletOutputStream(OutputStream output) {       
stream = new DataOutputStream(output);
public void write(int b) throws IOException {       
stream.write(b);
public void write(byte[] b) throws IOException {       
stream.write(b);
public void write(byte[] b, int off, int len) throws IOException {       
stream.write(b, off, len);