java.lang.IllegalStateException: Cannot forward after response has been committed

Question

    int noOfRows = Integer.parseInt(request.getParameter("noOfRows"));
    String chkboxVal = "";
    // String FormatId=null;
    Vector vRow = new Vector();
    Vector vRow1 = new Vector();
    String GroupId = "";
    String GroupDesc = "";
    for (int i = 0; i < noOfRows; i++) {
        if ((request.getParameter("chk_select" + i)) == null) {
            chkboxVal = "notticked";
        } else {
            chkboxVal = request.getParameter("chk_select" + i);
            if (chkboxVal.equals("ticked")) {
                fwdurl = "true";
                Statement st1 = con.createStatement();
                GroupId = request.getParameter("GroupId" + i);
                GroupDesc = request.getParameter("GroupDesc" + i);
                ResultSet rs1 = st1
                        .executeQuery("select FileId,Description from cs2k_Files "
                                + " where FileId like 'M%' and co_code = "
                                + ccode);
                ResultSetMetaData rsm = rs1.getMetaData();
                int cCount = rsm.getColumnCount();

                while (rs1.next()) {
                    Vector vCol1 = new Vector();
                    for (int j = 1; j <= cCount; j++) {
                        vCol1.addElement(rs1.getObject(j));
                    }
                    vRow.addElement(vCol1);
                }
                rs1 = st1
                        .executeQuery("select FileId,NotAllowed from cs2kGroupSub "
                                + " where FileId like 'M%' and GroupId = '"
                                + GroupId + "'" + " and co_code = " + ccode);
                rsm = rs1.getMetaData();
                cCount = rsm.getColumnCount();

                while (rs1.next()) {
                    Vector vCol2 = new Vector();
                    for (int j = 1; j <= cCount; j++) {
                        vCol2.addElement(rs1.getObject(j));
                    }
                    vRow1.addElement(vCol2);
                }

                // throw new Exception("test");

                break;
            }
        }
    }
    if (fwdurl.equals("true")) {
        // throw new Exception("test");
        // response.sendRedirect("cs2k_GroupCopiedUpdt.jsp") ;
        request.setAttribute("GroupId", GroupId);
        request.setAttribute("GroupDesc", GroupDesc);
        request.setAttribute("vRow", vRow);
        request.setAttribute("vRow1", vRow1);
        getServletConfig().getServletContext().getRequestDispatcher(
                "/GroupCopiedUpdt.jsp").forward(request, response);
    }

this function throw the above mentioned error and i am unable to spot the error area any help

Answer 1

Typically you see this error after you have already done a redirect and then try to output some more data to the output stream. In the cases where I have seen this in the past, it is often one of the filters that is trying to redirect the page, and then still forwards through to the servlet. I cannot see anything immediately wrong with the servlet, so you might want to try having a look at any filters that you have in place as well.

Edit: Some more help in diagnosing the problem…

The first step to diagnosing this problem is to ascertain exactly where the exception is being thrown. We are assuming that it is being thrown by the line

getServletConfig().getServletContext()
                  .getRequestDispatcher("/GroupCopiedUpdt.jsp")
                  .forward(request, response);

But you might find that it is being thrown later in the code, where you are trying to output to the output stream after you have tried to do the forward. If it is coming from the above line, then it means that somewhere before this line you have either:

1. output data to the output stream, or
2. done another redirect beforehand.

Good luck!

Answer 2

A common misunderstanding among starters is that they think that the call of a forward() or a sendRedirect() would magically exit and "jump" out of the method block, hereby ignoring the remnant of the code. For example:

protected void doPost() {
    if (someCondition) {
        sendRedirect();
    }
    forward(); // This is STILL invoked when someCondition is true!
}

This is thus actually not true. They do certainly not behave differently than any other Java methods (expect of System#exit() of course). When the someCondition in above example is true, then the chance is big that you will get an IllegalStateException: Cannot forward after response has been committed. This is regardless of whether the if statement calls a sendRedirect() or a forward().

To fix this, you need to add a return; statement afterwards

protected void doPost() {
    if (someCondition) {
        sendRedirect();
        return;
    }
    forward();
}

... or to introduce an else block.

protected void doPost() {
    if (someCondition) {
        sendRedirect();
    } else {
        forward();
    }
}

To naildown the root cause in your code, just search for any line which calls a sendRedirect() or a forward() without exiting the method block or skipping the remnant of the code. This can be inside the same servlet before the particular code line, but also in any servlet or filter which was been called before the particular servlet.

Unrelated to your actual problem: your JDBC code is leaking resources. Fix that as well.