Using request.getParameter to obtain caption of a Button throws NullPointerException

Question

i have created jsp file with three submit buttons pointing to one servlet,when i try to get the caption value as a request parameter in the servlet it throws a NullPointerException,the jsp file is here:

<td>
  <input type="submit" id="user" name="user_submit" value="search" class="searchUserbutton">
  </td>
<div class="searchResultFrameButtonDiv">
        <input type="submit" name="user_submit" id="addrole" value=">>" onClick="send_roles();" class="addDelsearchUserbutton"><br>

        <input type="submit" name="user_submit" id="deleterole" value="<<" onClick="delete_roles();" class="addDelsearchUserbutton">

    </div>

This is the code that throws NullPointerException in my servlet:

 String caps=request.getParameter("user_submit");
 System.out.println("the caps value is"+caps);// prints null

Answer 1

you are trying to get from submit button,use request.getParameter() to retrieve from text fields like <input type="text">

Also there is no form so submit button will not work

Answer 2

Don't give same name to multiple input elements , because in request.getParameter() method it will select parameter by name , so it will make ambiguity .

Change your code like this :

 <td>
  <input type="submit" id="user" name="user_submit" value="search" class="searchUserbutton">
  </td>
<div class="searchResultFrameButtonDiv">
        <input type="submit" name="user_submit_add" id="addrole" value=">>" onClick="send_roles();" class="addDelsearchUserbutton"><br>

        <input type="submit" name="user_submit_delete" id="deleterole" value="<<" onClick="delete_roles();" class="addDelsearchUserbutton">

    </div>

And in JSP page you can get parameter values by using corresponding parameter name.