Render a JSP page into HTML in a String

Question

I am using a mail template system that gets templates as JSP pages placed in /WEB-INF/mailtemplates/
I want to internally parse JSPs as if they were real JSPs in my tomcat but:
- Get get them using getResourceAsStream (or any other way)
- make JSP engine translate JSP into HTML into a String object.
- Send a mail with this HTML. (this part is already finished)
What I need is a method with the following proposed signature:
public String getMailTemplate(java.io.InputStream jspPageStream, javax.servlet.HttpServletRequest request) {}
The method must get the JSP from the stream, render it into the HTML and return it as a String.
Of course, it must render the JSP as a real JSP, using the apserver JSP engine. It must so replace any tags and EL objects:
${session.user.name} -> The name of the user
<c:forEach, ...
etc. etc. etc.
�Any ideas / directions on how to achieve this?
thanks,
Ignacio

Answer 1

Ok, just tried it out myself, and I'm getting the same result you are.
Nothing makes it out to the RedirectingServletResponse.
It appears to be buffering it somewhere in the included page.
If you put a command to flush the buffer on the jsp page being included: <% out.flush; %> then it works.
So why doesn't it work normally? Why doesn't the call to requestDispatcher.include (or forward) flush/commit its response?
I will admit to being stuck on this one. I'm figuring its something in the internal workings of Tomcat/JSP to do with when a page is flushed or not, but I can't thing of anything right now.
Here is the test I put together to try this out (along with a few corrections to my previous code). I will admit to being stumped :-)
The response wrapper:
package web;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintWriter;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
public class RedirectingServletResponse extends HttpServletResponseWrapper {
    RedirectServletStream out;
     * @param arg0
    public RedirectingServletResponse(HttpServletResponse response, OutputStream out) {
        super(response);
        this.out = new RedirectServletStream(out);
    /* (non-Javadoc)
     * @see javax.servlet.ServletResponse#flushBuffer()
    public void flushBuffer() throws IOException {
         out.flush();       
    /* (non-Javadoc)
     * @see javax.servlet.ServletResponse#getOutputStream()
    public ServletOutputStream getOutputStream() throws IOException {
        return out;
    /* (non-Javadoc)
     * @see javax.servlet.ServletResponse#getWriter()
    public PrintWriter getWriter() throws IOException {
        return new PrintWriter(out);
    /* (non-Javadoc)
      * @see javax.servlet.ServletResponseWrapper#getResponse()
     public ServletResponse getResponse() {
          return super.getResponse();
     /* (non-Javadoc)
      * @see javax.servlet.ServletResponseWrapper#setResponse(javax.servlet.ServletResponse)
     public void setResponse(ServletResponse arg0) {
          super.setResponse(arg0);
     private static class RedirectServletStream extends ServletOutputStream {
        OutputStream out;
        RedirectServletStream(OutputStream out) {
            this.out = out;
        public void write(int param) throws java.io.IOException {
            out.write(param);
A JSP using this class: requestWrapperTest.jsp
<%@ page import="java.io.*" %>
<%@ page import="web.RedirectingServletResponse" %>
<%@ page contentType="text/html;charset=UTF8" %>
<%!
public String getEmailText(HttpServletRequest request, HttpServletResponse response, String emailURL) {
     try{
       // create an output stream - to file, to memory...
       ByteArrayOutputStream out = new ByteArrayOutputStream();
       // create the "dummy" response object
       RedirectingServletResponse dummyResponse;
       dummyResponse = new RedirectingServletResponse(response, out);
       // get a request dispatcher for the email template to load 
       RequestDispatcher rd = request.getRequestDispatcher(emailURL);
       // execute that JSP
       rd.include(request, dummyResponse);
       // at this point the ByteArrayOutputStream has had the response written into it.
       dummyResponse.flushBuffer();
       byte[] result = out.toByteArray();
       System.out.println("result = " + result.length);
       // now you can do with it what you will.
       String emailText = new String(result);
       return emailText;
     catch (Exception e){
          e.printStackTrace(System.out);
          return "DANGER WILL ROBINSON!";
%>
<html>
<body>
<h2> Server Info Virtual!!</h2>
Server info = <%= application.getServerInfo() %> <br>
Servlet engine version = <%=  application.getMajorVersion() %>.<%= application.getMinorVersion() %><br>
Java version = <%= System.getProperty("java.vm.version") %><br>
<hr>
<%
  String result = getEmailText(request, response, "/testLoad.jsp");
  System.out.println(result);
%>
<%= result %>
</body>
</html>------------------------------------------------------------------
And the template page being included: testLoad.jsp
This is the page loaded for testing
<%
   System.out.println("in the inner jsp");
   // uncomment the following line to see this example work
   //out.flush();
%>