Question

I have a small servlet returning several html pages. The content of one of these pages is pretty complex, but changes only every hour or so. However, it is requested often by users. I want to avoid recomputing it at each request.

I was wondering whether it is possible to prepare a gzip-ed version in memory (byte array), and set it as the response to all HTML requests for this page. I would also recompute a new cached gzip-ed version every hour.

If this is possible, how can I do this? Should I use a filter? For the sake of this question, we can assume that all browsers can handle gzip-ed responses. I am looking for a code example.

Answer 1

After quite some googling, this seems to be the solution:

public class MyFilter implements Filter {

    private byte[] my_gzipped_page = ....

    public void doFilter(ServletRequest req, ServletResponse res,
        FilterChain chain) throws IOException, ServletException {

        if (req instanceof HttpServletRequest) {

            HttpServletRequest request = (HttpServletRequest) req;
            HttpServletResponse response = (HttpServletResponse) res;

            String ae = request.getHeader("accept-encoding");

            if (ae != null && ae.indexOf("gzip") != -1) {

                response.addHeader("Content-Length",
                    Integer.toString(my_gzipped_page.length)); 
                response.addHeader("Content-Encoding", "gzip");

                OutputStream output = response.getOutputStream();
                output.write(my_gzipped_page);
                output.flush();
                output.close();

                return;

            } else ...

        }
    }
    ...
}