A problem with a Filter

Question

I'm not sure whether filters shoud be discussed here - but I'll give it a try.
So, I'm having a filter that takes the response, changes it, and then prints it to the client (the way it is shown in the Sun tutorial)
out = res.getOutputStream();
response = (HttpServletResponse) res;
request = (HttpServletRequest) req;
MemoryResponseWrapper responseWrapper = new MemoryResponseWrapper(response);
filterChain.doFilter(request, responseWrapper);
responseText = responseWrapper.toString();
// some actions with the responseText
out.print(responseText);
out.flush();
out.close();
public class MemoryResponseWrapper extends HttpServletResponseWrapper {
    private CharArrayWriter mOutput;
    public MemoryResponseWrapper(HttpServletResponse response){
        super(response);
        mOutput = new CharArrayWriter();
    public String toString() {
        String result = mOutput.toString();
        return result;
     public PrintWriter getWriter() throws IOException {
          PrintWriter output = new PrintWriter(mOutput);
                                         return output;
}There are two scenarios:
- public void doFilter(..) { .. } - in this case the users' session are mixed - users get other users' pages instead of their own.
- public synchronized void doFilter(..) { .. } - the above problem is not occuring, but the pages load very slowly (probably due to the synchronization)
Also, I think it's important to mention - in the filter body I call request.getSession();
Using Tomcat 5.0, JDK 1.4.2
Message was edited by:
Glammy

Answer 1

Instead of synchronizing the doFilter() method, thereby making all requests to all servlets controlled by the filter wait in line, I think it would be better to try making the filter and servlets thread-safe. Not using class-level (instance or static) variables and only using local variables would go a long way towards completing that task.