sending/receiving json object using spring mvc

[serena5]

I am writing Spring web MVC app whereby the client and the server communicates by sending json messages.
On the client I am making asynchronous calls to update textboxes. Could you please let me know if I am using the right syntax? I have hit a brick wall and cannot see what I am doing wrong.
The function is called when user enters text in textbox. The application uses the code below to send char entered to server, the server returns a json object.

<script type="text/javascript">
          dojo.require("dijit.form.TextBox");
          dojo.require("dojo.parser");

          function convertToDecimal(){
            var targetNode = document.getElementById("key");
            var xhrArgs ={
              url: "/AjaxJavaDojo/",
              handleAs: "json",
              headers: {
                  "Content-Type": "text/json"
              },
              load: function(data){
                target.value = "load";
              },
              error: function(error){
                target.value = "error";
              }
            };
            //call asynchronously
            var deferred = dojo.xhrGet(xhrArgs);
          }
          dojo.addOnLoad(convertToDecimal);
          
        </script>