Problems with Compression Servlet Filter

[Reema Patel]

Hello All,
I have a simple requirement, I want to compress the response contents. I'm using a filter, wherein I first check if the browser supports zipping. I'm also printing debugging statements inside the write() method, they are getting printed but the problem is that I don't get to see anything on the page (its blank).

Pls. help..
Here is the code...

Filter Code

  
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.zip.GZIPOutputStream;
 
public class CompressionFilter implements  Filter{
  public CompressionFilter() {
  }
  private ServletContext ctx;
  private FilterConfig cfg;
 
    /**
     * The init method saves the config object and a quick reference to the
     * servlet context object (for logging purposes).
     */
  public void init(FilterConfig cfg)
         throws ServletException {
    this.cfg = cfg;
    ctx = cfg.getServletContext();
    ctx.log(cfg.getFilterName() + " initialized.");
  }
 
    /**
     * The heart of this filter wraps the response object with a Decorator
     * that wraps the output stream with a compression I/O stream.
     * Compression of the output stream is only performed if and only if
     * the client includes an Accept-Encoding header (specifically, for gzip).
     */
  public void doFilter(ServletRequest req,
                       ServletResponse resp,
                       FilterChain fc)
         throws IOException, ServletException {
    HttpServletRequest request = (HttpServletRequest) req;
    HttpServletResponse response = (HttpServletResponse) resp;
 
    // Dose the client accept GZIP compression?
    String valid_encodings = request.getHeader("Accept-Encoding");
    if ( (valid_encodings != null) && (valid_encodings.indexOf("gzip") > -1) ) {
 
      // Then wrap the response object with a compression wrapper
      // We'll look at this class in a minute.
      RMCompressionResponseWrapper wrappedResp
        = new RMCompressionResponseWrapper(response);
getGZIPOutputStream
      // Declare that the response content is being GZIP encoded.
      //wrappedResp.setHeader("Content-Encoding", "gzip");
wrappedResp.addHeader("Content-Encoding", "gzip");
 
      // Chain to the next component (thus processing the request)
      fc.doFilter(request, wrappedResp);
 
      // A GZIP compression stream must be "finished" which also
      // flushes the GZIP stream buffer which sends all of its
      // data to the original response stream.
      GZIPOutputStream gzos = wrappedResp.getGZIPOutputStream();
      gzos.finish();
      // The container handles the rest of the work.
 
      ctx.log(cfg.getFilterName() + ": finished the request.");
 
    } else {
      fc.doFilter(request, response);
      ctx.log(cfg.getFilterName() + ": no encoding performed.");
    }
  }
 
  public void destroy() {
      // nulling out my instance variables
      cfg = null;
      ctx = null;
  }
 
 
}  

Customized Response Wrapper Code

import javax.servlet.http.HttpServletResponseWrapper;
 
import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
import java.util.zip.GZIPOutputStream;
 
public class CompressionResponseWrapper extends HttpServletResponseWrapper {
 
  /** the compressed output stream for the servlet response */
    private GZIPServletOutputStream servletGzipOS = null;
 
    /** the PrintWriter object to the compressed output stream */
    private PrintWriter pw = null;
 
    /**
     * The constructor performs the Decorator responsibility of storing
     * a reference to the object being decorated, in this case the HTTP
     * response object.
     */
    CompressionResponseWrapper(HttpServletResponse resp) {
      super(resp);
    }
 
    //
    // Override HttpServletResponse methods to use our stream objects
    //
 
    /**
     * This state variable holds the first stream object created.
     */
    private Object streamUsed = null;
 
    /**
     * Provide access to a decorated servlet output stream.
     */
    public ServletOutputStream getOutputStream() throws IOException {
        // Allow the servlet to access a servlet output stream (SOS)
        // only if the servlet has not already accessed the print writer.
/*      if ( (streamUsed != null) && (streamUsed != servletGzipOS) ) {
        throw new IllegalStateException();
      }*/
      // Wrap the original servlet output stream with our compression SOS.
      // We'll look at this class in a minute.
      if ( servletGzipOS == null ) {
        servletGzipOS
            = new GZIPServletOutputStream(getResponse()
                                          .getOutputStream());
        streamUsed = servletGzipOS;
      }
      return servletGzipOS;
    }
 
    /**
     *  Provide access to a decorated print writer.
     */
    public PrintWriter getWriter() throws IOException {
      // Allow the servlet to access a print writer only if the
      // servlet has not already accessed the servlet output stream.
     /* if ( (streamUsed != null) && (streamUsed != pw) ) {
        throw new IllegalStateException();
      }*/
      // To make a print writer, we have to first wrap the servlet output stream
      // and then wrap the compression SOS in two additional OS decorators:
      // OutputStreamWriter which converts characters into bytes, and then a
      // PrintWriter on top of the OSWriter object.
      if ( pw == null ) {
        servletGzipOS
            = new GZIPServletOutputStream(getResponse().getOutputStream());
        // Use the response charset to create the OSWriter
        OutputStreamWriter osw
            = new OutputStreamWriter(servletGzipOS,
                                     getResponse().getCharacterEncoding());
        // Wrap the OSWriter in the PrintWriter
        pw = new PrintWriter(osw);
        streamUsed = pw;
      }
      return pw;
    }
 
    /**
     * Ignore this method, because the real output will be compressed.
     */
    public void setContentLength(int len) { }
 
    //
    // Decorator methods (used by the Filter)
    //
 
    /**
     * This gives the compression filter a handle on the GZIP output stream
     * so that it (the filter) can "finish" and flush the GZIP stream.
     */
    public GZIPOutputStream getGZIPOutputStream() {
      return this.servletGzipOS.internalGzipOS;
    }
  }
 
 
  /**
   * This helper class is a Decorator on the ServletOutputStream abstract
   * class which delegates the real work of compressing the generated content
   * using a standard GZIP output stream.
   *
   * There is only one abstract method in the SOS class which this Decorator
   * must implement: write(int).  This is where all of the delegation magic
   * occurs.
   */
  class GZIPServletOutputStream extends ServletOutputStream {
 
    /**
     * Keep a reference to raw GZIP stream.
     * This instance variable is package-private to allow the compression
     * response wrapper access to this variable.
     */
    GZIPOutputStream internalGzipOS;
 
    /** Decorator constructor */
    GZIPServletOutputStream(ServletOutputStream sos) throws IOException {
      this.internalGzipOS = new GZIPOutputStream(sos);
    }
 
    /**
     * This method implements the compression decoration by delegating the
     * write() call to the GZIP compression stream, which is wrapping the
     * original servlet output stream, which is (ultimately) wrapping the
     * TCP network output stream to the client.
     */
    public void write(int param) throws java.io.IOException {
      System.out.println("]]]]]]]]]]]]]INSIDE WRITE(INT) METHOD[[[[[[[[[[[[[[");
      internalGzipOS.write(param);
    }
    public void write(byte b[]) throws IOException {
        System.out.println("]]]]]]]]]]]]]INSIDE WRITE(BYTE[]) METHOD[[[[[[[[[[[[[[");
        internalGzipOS.write(b, 0, b.length);
      }
 
      public void write(byte b[], int off, int len)
          throws IOException {
        System.out.println("]]]]]]]]]]]]]INSIDE WRITE(BYTE[],INT,INT) METHOD[[[[[[[[[[[[[[");
        internalGzipOS.write(b, off, len);
      }
 
 
 
}
   

The problem is that i'm getting a blank page.
I have tried to run on IE 6 and Mozilla 5.0 and I'm using Tomcat 5 at the web container.

Thanks,
Reema

[ August 07, 2006: Message edited by: Reema Patel ]
[ August 07, 2006: Message edited by: Reema Patel ]

[Bear Bibeault]

Please use UBB code tags when posting more than one line of code.

[Reema Patel]

[Thread hi-jack removed. Reema, please ask your questions in your own topics that you open. Do not hi-jack other people's topics.]
[ August 08, 2006: Message edited by: Bear Bibeault ]

[Ben Souther]

Tomcat has compression built in.
You just have to turn it on.

Look for the "compression" attribute in this http connector config page:
http://tomcat.apache.org/tomcat-5.5-doc/config/http.html

[Reema Patel]

Hey,
I can now run the filter code on BEA WLS, but the problem is that it is showing junk text. Also, ironically the filter mechanism is taking along time.
Reema

[Ben Souther]

Originally posted by Reema Patel:
Hey,
I can now run the filter code on BEA WLS, but the problem is that it is showing junk text. Also, ironically the filter mechanism is taking along time.
Reema

I thought you said you were using Tomcat. ? .
[ August 11, 2006: Message edited by: Ben Souther ]

[Reema Patel]

HI Ben,
Thanks for the post.
Earlier I used Tomcat 5.
This time I'm using WLS 8

Thanks,
Reema