Flushing output stream is ignored in a Servlet under Tomcat via AJP

Question

Suppose I have a Java Servlet that takes a while to finish computing it's response, but I'd like the client to see intermediate response rather than wait for it to finish. For example, suppose I have the following doGet code:

protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
{
    resp.setContentType("text/html");
    PrintWriter out = new PrintWriter(resp.getOutputStream());

    out.println("<h1>The Title</h1>");
    out.flush();

    // ... some computation that takes a while

    // ... now print the result via out

    out.close();
}

When I am running Tomcat locally, and accessing the Servlet, I can see the <h1> before the entire computation is completed.

However, when I run it on my server, and access it via Apache, I only get the response after the entire request is completed (in other words, I get a blank screen instead of the <h1> which I expect to receive).

I suspect that the issue is somewhere in AJP or Apache, seems like it's ignoring the calls to flush(), but I can't seem to find where the problem is.

On the server I'm using Tomcat 6, Apache 2.2.21 and AJP 1.3

Answer 1

Turned out all I needed was to build the APR based Native library for Tomcat. After properly building and installing it based on the instructions here, it worked fine with AJP.