Why do I get "Cannot forward after response has been committed"?

I've writing my first servlet and based it on the sample "CurrentUserServlet.java".

I think this should work but it gives me the error:


RequestDispatcher view = request.getRequestDispatcher("pfg/workareas.jsp");
view.forward(request, response);

Instead, I need to do this:


request.getRequestDispatcher( "pfg/workareas.jsp").include( request, response);

Is this "just the way it is done" in TeamSite? At the java ranch forums, using include was described as "very sloppy code".

Does anybody know *why* that include has to be used?

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vpatel

You need to provide more information on this. It seems like a customization to me.

Migrateduser

You need to provide more information on this. It seems like a customization to me.

Lot's more detail can be seen here: http://www.coderanch.com/t/462031/Servlets/java/Why-do-get-Cannot-forward

Is there something specific you need to see?

Migrateduser

You need to provide more information on this. It seems like a customization to me.

I started with "CurrentUserServlet" provided by Autonomy as my example. The UI customization docs do say that there needs to be filter-mapping in web.xml, but that sample servlet seems to work with or without it.

On the servlet I started, I simply copied their code as a starting point. I do a bit and then attempt to use a JSP to display the output. It only works if I use include, not forward.

Here is the actual code:

    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException
    {
        // get the cs client
        CSClient client = (CSClient)request.getAttribute( "iw.csclient");

        if ( !client.isValid() ) {
            throw new ServletException( "No valid user");
        } else {
            // valid client, so get their workareas

            // Gets the current user
            CSUser user = client.getCurrentUser();

            FilesHelper fh = new FilesHelper();
            List result = fh.getWorkareas(user, client);

            request.setAttribute("workareas", result);
            request.getRequestDispatcher( "pfg/workareas.jsp").include( request, response);

            //RequestDispatcher view = request.getRequestDispatcher("pfg/workareas.jsp");
            //view.forward(request, response);
    }
}

vpatel

Lot's more detail can be seen here: http://www.coderanch.com/t/462031/Servlets/java/Why-do-get-Cannot-forward

Is there something specific you need to see?

Sorry for not being clear. What I meant is that can you provide some context of what this Java customization is supposed to do? How is it being accessed? Any other relevant information.

Migrateduser

Sorry for not being clear. What I meant is that can you provide some context of what this Java customization is supposed to do? How is it being accessed? Any other relevant information.

The intent is to provide two portlets in ccStd that show locked or modified files (excluding the DCR's). The user will be able to select a workarea and toggle the view between only their own files that are locked or modified and all locked or modified files in that workarea.

My plan was to write a servlet and use JSP's to display the content. I'm assuming that I will need to use some Javascript to make calls to the servlet again when they want to between "all" and "only theirs". Have it do an "auto post".

Did that help you?

Crsb

The intent is to provide two portlets in ccStd that show locked or modified files (excluding the DCR's)...

My plan was to write a servlet and use JSP's to display the content. I'm assuming that I will need to use some Javascript to make calls to the servlet again when they want to between "all" and "only theirs". Have it do an "auto post".

Did that help you?

1) do you want this portlet to always show up when the user is in the home view in ccstd? for this (once you got your logic working) you just add your servlet or jsp page as a portlet in ui_custom and it should load the portlet with the data once the user is in the home view, but you will need action button/link in your portlet two switch between all and "only theirs", button would just be a call to you servlet with different attribute to return the desired data.

2)or you want this portlet to only show up if a user selects or clicks on an action? this will need extra coding to make it happen

Migrateduser

1) do you want this portlet to always show up when the user is in the home view in ccstd? for this (once you got your logic working) you just add your servlet or jsp page as a portlet in ui_custom and it should load the portlet with the data once the user is in the home view, but you will need action button/link in your portlet two switch between all and "only theirs", button would just be a call to you servlet with different attribute to return the desired data.

2)or you want this portlet to only show up if a user selects or clicks on an action? this will need extra coding to make it happen

Option 1 is our goal.

Bjorn

At the most basic and boring level you're getting that exception because....the response has already been committed before you call the RequestDispatcher.forward(). The reason the include() works is because an include and a forward are two different things. An include is getting the content of a resource (in this case, your JSP) and including it in the response. A forward is forwarding the request to another resource. You can't forward (or redirect) something that's already been committed to go somewhere else, so to speak. Maybe I'm telling you what you already know.

Anyhow, for starters, when you say "it gives me the error", where do you get this error? In a log file? Or do you get it in your browser as a 500 error when you access the URL to which you've mapped this servlet? Is there a stack trace for the IllegalStateException? That might be handy to see.

Migrateduser

I found some more code by another Interwove/Autonomy developer from a GearUp session. In his code, he explains it like this:

//Note that we use RequestDispatcher.include() rather than forward().
//This is because we are part of a portal page, and our response is
//only part of the total response to this http request.

Bjorn

I found some more code by another Interwove/Autonomy developer from a GearUp session. In his code, he explains it like this:

Good info. So if I understand you, this was for CCStd and not just a random servlet on its own? I don't know much about CCStd because we don't use it, but it makes sense given pg. 96 of UI Customization Guide. Or am I way off base?

----

ContentCenter Standard portlets differ from other UITK GUI elements in that they are attached internally to the ContentCenter home page using a Java include. (This is also true for wizard topic help questions, which are attached to ContentCenter Standard’s wizards with a Java include.)
A a result, a portlet element’s url attribute cannot be a URL to:
- An HTML page.
- A servlet or JSP that outputs HTML with HTML, HEAD, or BODY tags.
- A servlet the performs a forward or redirect.

Within these limits, a portlet can access static web content or external web pages through a JSP or servlet.

Migrateduser

Good info. So if I understand you, this was for CCStd and not just a random servlet on its own? I don't know much about CCStd because we don't use it, but it makes sense given pg. 96 of UI Customization Guide. Or am I way off base?

----

ContentCenter Standard portlets differ from other UITK GUI elements in that they are attached internally to the ContentCenter home page using a Java include. (This is also true for wizard topic help questions, which are attached to ContentCenter Standard’s wizards with a Java include.)
A a result, a portlet element’s url attribute cannot be a URL to:
- An HTML page.
- A servlet or JSP that outputs HTML with HTML, HEAD, or BODY tags.
- A servlet the performs a forward or redirect.

Within these limits, a portlet can access static web content or external web pages through a JSP or servlet.

Yup, you got it.

Thank you for that last line! I can't believe I missed that in the guide!