[SOLVED] Servlet filter for caching

Servlet filter for caching

I'm creating a servlet filter for caching. The idea is to cache the response body to memcached. The response body is generated by (result is a string):

 response.getWriter().print(result);

My question is that, since the response body will be put into the memcached without modification, do I still need to create a customized HttpServletResponseWrapper? Can anyone provide any skeleton code for this filter?

Solution

You need to be able to capture the servlet's output in your filter.

For this, you need to inject a customized HttpServletResponseWrapper that collects all output sent to getWriter().print() somewhere so that you can hand it off to memcached.

Maybe something along the lines of:

ByteArrayOutputStream baos = new ByteArrayOutputStream(3000); 
final PrintWriter w = new PrintWriter(new OutputStreamWriter(baos, "UTF-8"));

HttpServletResponse wrapper = new HttpServletResponseWrapper(response) {

    @Override
    public PrintWriter getWriter() throws IOException {
        return w;
    }

};

If this is a bigger project and you have more control over the network infrastructure, it might also be a good idea to not do this in Java, but just use a separate proxy server in front of the Servlet container. You can control what should be cached by the usual Cache-Control HTTP headers (which you can set using a filter if the servlet does not already do it).