JSONP callback function not working correctly

Question

I have jsonp callback functionalty. Response coming from server is undefined.I do not know where the problem is. I have made RND for jsonp. I am posting code

$.ajax({
         url : 'http://192.168.16.111:8081/MiddleWareUsman/androidServlet', 
         type: "GET",
         dataType: "jsonp",         
         crossDomain: true,
         async: false,
         data : {"fname": "chaaaaapiio","lname": "gya"},            
         jsonpCallback:  function(data, status){
            alert('callback');
            alert(data);
         },            
         success: function(data, status){
            alert('sucess');
         },
     error : function(xhr, ajaxOptions, thrownError) {          
         alert(thrownError);                        
         }
  });

And Servlet code is

        String a=request.getParameter("fname");
        String b=request.getParameter("lname");
        String cb=request.getParameter("callback");     
        response.getWriter().write(cb+"("+a+" "+b+")");

Answer 1

First, jsonpCallback is used when you want to override the default function name. If you assign a function to it, then the return value of that function should be the name. Giving it a function that returns undefined is just going to break things.

Remove the jsonpCallback property from your object . Handle things in success .

Second, that servlet code is going to generate:

jQueryCallback23235(chaaaaapiio gya)

This isn't valid JavaScript. You need to have a real JavaScript data structure as your function arguments.

Typically, a JSONP response would consist of an object literal:

jQueryCallback23235({ "something": "chaaaaapiio", "something": "gya")

Find a Java library for generating JSON and use that to produce the contents of the parens, don't try to write JSON by hand.