how to check if the a button has been pressed (in a jsp file)

Question

I am working on a JSP file(don't want to use a servlet), I have a simple form, 2 labels, 2 inputs and 2 buttons, and I want to print out the submitted string on the same jsp page , the problem is that the last values submitted remain printed on the screen as I try new ones, that is why I thought of a test to check whether the button submit was clicked before we move to the display, I tried this code :

       <body>
       <form  method='post'>
       <pre>
       <label>Username</label> <input type="text" name="user"  required/>
       <label>Password</label> <input type="password" name="pwd" required />
       <br>
       <input type="submit" value="confirm" name ="submit" /> 
       <input type="reset" value="clear"  /> 
       </pre>
       </form>
       <br>
       // test if the submit button was clicked (check if value of submit is confirm)

        <% String x=request.getParameter("submit")%>
        <% if (x.equals("confirm")){ %>

       <% if (request.getParameter("user")!="" && request.getParameter("pwd")!=""){ %>
       <center>
       <h4> user is : <% out.write(request.getParameter("user")); %> </h4>
       <br> 
       <h4> password is : <% out.write(request.getParameter("pwd")); %> </h4>
       </center>
       <% } else {  %>

        <h4> inputs r empty !! </h4> 

       <% } %>
       <% } %>
       </body>

I get an error at line :

       <% if (x.equals("confirm")){ %>

any idea why ?

developerwjk · Answer 1 · 2014-03-27T21:03:53.377

First of all, stop opening and closing JSP tags unnecessarily. Its sloppy and unreadable. Secondly, you're missing a semi-colon. Third, you need to check for the possibility that the parameter is null. When the form was not submitted, the parameter is null.

This is bad:

 <% String x=request.getParameter("submit")%>
 <% if (x.equals("confirm")){ %>

Do it like this:

 <%
   String x = request.getParameter("submit");
   if(x!=null && x.equals("confirm"))
   {
     ...

You could also reverse the string comparison. If you use a dot operator on a variable that is null, you get a null pointer exception. So you could use the dot operator on the string literal, and thus avoid explicitly checking for null:

 <%
   String x = request.getParameter("submit");
   if("confirm".equals(x))
   {
     ...

Also once you fix this, you will run into a problem with if (request.getParameter("user")!="". You need to use .equals() because in Java for String ==, != do not compare string contents, but compare pointer (i.e. memory address) equivalence.

score 0 · Answer 2 · answered Sep 14 '17 at 11:08

This question seems not too much old . So I can safely add an answer to this question .

Basically when you want to process submitted form data in same page , you cab use the following code snippet :

    <%
    String check_submit_form = request.getParameter("submit");
    if((request.getParameter("btnLogon") == null)?false:true){
            for(int i =0;i<=100;i++){
                 out.println("Congrts Bro . you have done a great job .");
            }
    }
    else{
    %>

   <form name="form_logon" method="POST" action ="logonHome.jsp">
     <input type="submit" value="Click for Finger Verification" name="btnLogon">
  </form>
  <%
   }
  %>

The code is self-explanatory . If you hit the submit button , then you can process the form otherwise you will be redirected to the form . Hope this helps .

how to check if the a button has been pressed (in a jsp file)

2 Answers2