IllegalStateException while using JSP
Applies to:
NA
Description:
Signals that a method has been invoked at an illegal or inappropriate time. In other words, the Java environment or Java application is not in an appropriate state for the requested operation.
Cause:
a. The most common cause of this exception is a servlet or JSP attempting to write to the output stream after the response has been committed.
b. Another way this can happen is by attempting to redirect from within the middle of a JSP page:
…
<%
if ("not logged in")
response.sendRedirect("login.jsp");
%>
…
c. Another common place where an IllegalStateException is likely to occur is in a JSP that attempts to stream binary data. JSPs are primarily designed to format output as HTML. With HTML, white space characters are ignored. It is not uncommon for JSP compilers to inject their own white space charaters to the beginning and/or end of the output stream. Line breaks in the developer’s code can also be interpreted as white space in the output stream. These white space characters can interfer with the generated servlet’s ability to create and stream the binary outputdata, resulting in the IllegalStateException.
a. For servlets, the easiest way to avoid this is to branch the code in your service method in such a way as to insure that calls to HttpServletResponse.sendRedirect or RequestDispatcher.forward are always the last call made before the end of the method. This can be achieved by adding a return call just after either of these.
Example:
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException{
if(“client”.equals(request.getParameter(“user_type”))){
response.sendRedirect(“client-screen.jsp”);
return; // <——- This return statement prevents any further writing to the outputStream
}
//
// Other code that may write to the outputStream….
//
}
b. It is impossible to redirect from within the middle of a JSP page. Check this and correct the code.
c. The simple solution to this problem is to always us a servlet for streaming binary data.