RequestDispatcher showing error??

[Joe San]

Hi Guys,

I tried the code as below,

protected void service (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String pp = request.getParameter("login");
//System.out.println(pp);
//PrintWriter out = response.getWriter();
ServletOutputStream os = response.getOutputStream();
os.print("This is before the forward");
RequestDispatcher view = request.getRequestDispatcher("/test.jsp");
view.forward(request, response);
System.out.println("Printed after the forward");
}

I call the above servlet from my jsp called test.jsp and forward it using the requestdispatcher to the same jsp again. When I tried the above example, I got the following error...

java.lang.IllegalStateException: getOutputStream() has already been called for this response
org.apache.coyote.tomcat5.CoyoteResponse.getWriter(CoyoteResponse.java:599)
org.apache.coyote.tomcat5.CoyoteResponseFacade.getWriter(CoyoteResponseFacade.java:163)
org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:122)
org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:115)
org.apache.jasper.runtime.PageContextImpl.release(PageContextImpl.java:190)
org.apache.jasper.runtime.JspFactoryImpl.internalReleasePageContext(JspFactoryImpl.java:115)
org.apache.jasper.runtime.JspFactoryImpl.releasePageContext(JspFactoryImpl.java:75)
org.apache.jsp.test_jsp._jspService(test_jsp.java:67)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
com.example.ExampleServlet.service(ExampleServlet.java:28)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

[Joe San]

But when I tried PrintWriter outp = response.getWriter(); instead of ServletOutpurStream, I'm getting the desired o/p??

[Joe San]

What happens if I do the forward using a jsp:forward say in a jsp page and If I use ServletOutputStream, will I still get IllegalStateException??

[Joe San]

Any help ranchers?? Satou I was expecting your reply!

[Sergio Tridente]

Ooof. This is a tough one. I'll try to answer it using the specs.

Accordingly to JSP.12.2.3:

The initial JspWriter object is associated with the PrintWriter object of the ServletResponse in a way that depends on whether the page is or is not buffered.
If the page is not buffered, output written to this JspWriter object will be written through to the PrintWriter directly, which will be created if necessary by invoking the getWriter() method on the response object. But if the page is buffered, the PrintWriter object will not be created until the buffer is flushed and operations like setContentType() are legal. Since this flexibility simplifies programming substantially, buffering is the default for JSP pages.

And SRV.14.2.22 states:

getOutputStream()
Throws:
IllegalStateException - if the getWriter method has been called on this response

getWriter()
Throws:
IllegalStateException - if the getOutputStream method has already been called for this response object

In your case, what happened is that you first called ServletResponse.getOutputStream() in your servlet and then after forwarding to the jsp page, the jsp page tried to obtain the JspWriter which in turn is bounded to a PrintWriter object (this means that at some point there is a call to ServletResponse.getWriter()). In the end, you finished calling getOutputStream() and getWriter() on the same ServletResponse object. That's why you've got a IllegalStateException.

The same would be true if you forward from your jsp page to the servlet that uses the ServletOutputStream.

My conclusion would be: if you are forwarding from/to a jsp page, don't use ServletResponse.getOutputStream().
[ April 30, 2007: Message edited by: Sergio Tridente ]

[Napu Sun]

Thanks, Sergio.
You made this very clear. I tested it works in the way what you pointed out: we cannot invoke getOutputStream and getWriter in the same response object.

[Joe San]

Sergio,

When I tried this example by uncommenting the PrintWriter out = response.getWriter() and commented the outputstream, I'm able to run it without any errors...

[Joe San]

I tried the following,

The service method,

protected void service (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String pp = request.getParameter("login");

PrintWriter outp = response.getWriter();

outp.print("This is the output from the servlet");
outp.flush();
RequestDispatcher view = request.getRequestDispatcher("/test.jsp");
view.forward(request, response);
System.out.println("Printed after the forward");
}

I try to access this servlet from a jsp and I'm getting the o/p as "This is the output from the servlet". It should have thrown an IllegalStateException right as we are doing the forward after the response is comitted?? But at the same time when I try using the ServletOutputStream as below I'm getting the same o/p???,

protected void service (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String pp = request.getParameter("login");
//System.out.println(pp);
//PrintWriter outp = response.getWriter();
ServletOutputStream outp = response.getOutputStream();
outp.print("This is the output from the servlet");
outp.flush();
RequestDispatcher view = request.getRequestDispatcher("/test.jsp");
view.forward(request, response);
System.out.println("Printed after the forward");
}

This is my test.jsp in both cases

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<form action="ExampleServlet" method="POST">
Login Name: <input type="text" name="login">
<input type="submit" value="SUBMIT">
<% out.println("This is written by the jsp");%>
 
</form>
</body>
</html>

[Joe San]

If I don't use the line outp.flush(), then with the ServletOutputStream, I'm getting an IllegalState but when I use a PrintWriter (without the line outp.flush()), I'm not getting an IllegalState and I'm able to see the desired o/p?? WHY???

[Joe San]

Guys,

What is the whole catch with RequestDispatcher.forward, jsp:forward and the flush method call?? Can anyone summarize this here?? I could have summarized it in my SCWCD Hints page but still I'm dubious about flush() call and the ServletOutputStream...as I posted my question above...

[Sergio Tridente]

First:
getOutputStream() and getWriter() on the same ServletResponse object is a NO NO. Take a look at my first post to find the spec's citation.

Originally posted by Jothi Shankar Kumar Sankararaj:
I try to access this servlet from a jsp and I'm getting the o/p as "This is the output from the servlet". It should have thrown an IllegalStateException right as we are doing the forward after the response is comitted?? But at the same time when I try using the ServletOutputStream as below I'm getting the same o/p???,

My bet is that it is throwing the exception but you are not seeing it in the browser because... the reponse had already been commited. Try writing to the console to see what happens (catch the exception and write to the console).

[Joe San]

Yeah, you are right sergio. Maybe I will try that. Can you summarize the whole thing related to RequestDispatcher and flush??