如何从servlet到jsp获得响应？

Question

I am trying get response from servlet use

request.setAttribute(error, error);
request.getRequestDispatcher("http://localhost:8080/redicted_test/Home.jsp").forward(request, response);

String redictedURL="http://localhost:8080/redicted_test/Home.jsp";
response.sendRedirect(redictedURL);

But get error

java.lang.IllegalStateException: Cannot call sendRedirect() after the response has been committed

Im understand that im send response twice, but how i can do it else? Can u tell me simplest way?

Answer 1

You already have forwarded the request and now you are redirecting it

request.getRequestDispatcher("http://localhost:8080/redicted_test/Home.jsp").forward(request, response);
..
response.sendRedirect(redictedURL);

If you want to set some attributes from servlet and need to display it on jsp, then just forward the request to jsp and display those attributes

Answer 2

In your example you have executed the jsp and the rendered jsp was sent in the response buffer. And since you have started to send the response, the response headers were sent. But just after that you wanted to send redirection and a redirection is a kind of headers manipulation (changes http status code and location headers).

Answer 3

i think u should use include rather then forward ..

forward is used to forward a request, that is control is transfered to the
new servler/jsp. u shud take care to not put any our.println() statements 
in the servlet from where u plan to call forward method. in fact u cant even 
fire response.getWriter() method in this case. u can only do that in the servlet
to which the control is bein fwded 

Never write any thing to response if you are going to forward the request to another servlet or JSP. For example, if Servlet1 forwards the request to Servlet2, Servlet1 should not write any thing to response, neither call the response.getOutputStream() method.This is not allowed and either whatever servlet1 wrote to the response will not output or you will get IllegalStateException.

include - means that the new servlet/jsp will be procesed and any
out.println()/html stuff will be included and then control will come
back to the servlet/jsp that called include method. 

Answer 4

After a RequestDispatcher.forward() , the response will be committed and closed. You cannot write any header/content to the response.

That is why you cannot redirect or do operation which adds header or response content after doing RequestDispatcher.forward() .

The alternative you have is use include instead of forward.

But, i did not understand your use case. You are forwarding and redirecting to the same page.