JQuery ajax post - data in a java servlet

Question

I want to send data to a java servlet for processing. The data will have a variable length and be in key/value pairs:

{ A1984 : 1, A9873 : 5, A1674 : 2, A8724 : 1, A3574 : 3, A1165 : 5 }

The data doesn't need to be formated this way, it is just how I have it now.

var saveData = $.ajax({
      type: "POST",
      url: "someaction.do?action=saveData",
      data: myDataVar.toString(),
      dataType: "text",
      success: function(resultData){
          alert("Save Complete");
      }
});
saveData.error(function() { alert("Something went wrong"); });

The $.ajax() function works fine as I do get an alert for "Save Complete". My dilemna is on the servlet. How do I retrieve the data? I tried to use a HashMap like this...

HashMap hm = new HashMap();
hm.putAll(request.getParameterMap());

...but hm turns out to be null which I am guessing means the .getParameterMap() isn't finding the key/value pairs. Where am I going wrong or what am I missing?