how to stop servlet?

Question

I have a servlet that looks like this:

public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException{
    String param1 = request.getParameter("param1");
    String param2 = request.getParameter("param2");

    validateInput(param1, param2, request, response);

    //if nothing's wrong with the input, do this and that
}


private void validateInput(String param1, String param2, HttpServletRequest request, HttpServletResponse response) throws IOException{
    boolean fail = false;

    //validate input blah blah blah

    if (fail){
        PrintWriter out = response.getWriter();
        out.write("invalid input");
        //end process or servlet
    }
}

The idea is that I want to pass param1 and param2 to function validateInput() to validate whether or not the input is valid. If input is invalid, write a message back and then end the process. My question is how to end the process? I'm aware of that calling return; in doPost() will end the process but I'm trying to avoid returning any value from validateInput() to doPost() just for the sake of ending the process. I personally feel that it's more readable this way rather than returning true or false to doPost() and call return; there. Is there a way to do it? Or is it simply impossible?

Answer 1

public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException{
    String param1 = request.getParameter("param1");
    String param2 = request.getParameter("param2");

    if(!isValidInput(param1, param2)){
        PrintWriter out = response.getWriter();
        out.write("invalid input");
        return;
    }

    //if nothing's wrong with the input, do this and that

}


private boolean isValidInput(String param1, String param2){
    boolean fail = false;
    //validate input and return true/false

}

Answer 2

Control will always return to doPost after validateInput runs unless you throw an exception (either an unchecked exception or IOException in this case).

So if you do not return ANY value from validateInput to doPost, even if you commit the response, doPost will still go on to do whatever it is supposed to do. (Of course, if the response is commited, the browser will be entirely unaware of any further activity on the server side).

You will need to return a value, throw an exception (which doPost may catch) or set a global value that doPost checks (which is just messy).