RE: [Tomcat 4.1] Caching JSP Output via Filter PLZ HELP!!

[Jacob Hookom]

I did something very similar to what you have here, but I did a
DualServletOutputStream where if the printwriter was requested from the
HttpServletResponseWrapper, I would return a new PrintWriter that wrapped my
DualServletOutputStream.  The dual output stream contains the
super.getOutputStream() (the actual response output) and the
BufferedOutputStream that is used to getByteArray() and cache it.

It's very strange though because again, HTML files are successfully cached
and I can even look at the serialized content on the file system, but 0
bytes are written from JSP requests, even though I can see in my Log4j
output that indeed the getWriter() method was called on my
HttpServletResponseWrapper.

Best Regards,
Jacob Hookom

-----Original Message-----
From: li pan [mailto:[EMAIL PROTECTED]] 
Sent: Friday, January 24, 2003 11:01 PM
To: [EMAIL PROTECTED]
Subject: RE: [Tomcat 4.1] Caching JSP Output via Filter PLZ HELP!!


Hello Jacob
  I have successfully implemented this idea. I guess you mean that get the 
writer of JSP, and replace the writer with another one which will cache the 
jsp results as well as output them to the original writer? Yes, it works.
  I didn't use a filter, I simply hacked tomcat, so that my cache facility 
can be used by any web applications without modifying source codes of them.
  But I didn't get trouble by getWriter(), I guess maybe :
1 before you get the writer from the filter, tomcat has already done 
something to the writer? I get it right after the JSP instance is built.
2 tomcat does not allow you to change the writer of a response while it is 
in the filter chain? I also replace the response with my own wrapper, so I 
don't change it.

Here is my buffered writer:

package servercache;
import java.io.PrintWriter;
import java.nio.CharBuffer;
public class BufferedPrintWriter
    extends PrintWriter {

    private PrintWriter writer;
    private CharBuffer buffer = CharBuffer.allocate(1024);

    public BufferedPrintWriter(PrintWriter writer) {
        super(writer); //doesnot make any sense.
        this.writer = writer;
    }

    public void write(char[] buf, int offset, int count) {
        writer.write(buf, offset, count);
        buffer.put(buf, offset, count);
    }

    public void write(String str) {
        writer.write(str);
        buffer.put(str);
    }

    public void print(String str) {
        writer.print(str);

        if (str == null) {
            buffer.put("null");
        } else {
            buffer.put(str);
        }
    }

    public void println(String str) {
        writer.println(str);
        buffer.put(str);
        buffer.put("\n");
    }

    public CharBuffer getBuffer() {

        return buffer;
    }
}

and here is how it is created:

writer = new BufferedPrintWriter(response.getWriter());



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