Bad request on post json data in Angularjs and spring mvc

i want to post json data to spring mvc controller by Angularjs. For this purpose i wrote this code. but when i post form bad request error display in console.for simple data it work correctly but for nested object not work. how i post nested json object to controller?

my entity :

 public class TestData {
  private String name;
  private List<TestData2> data;
 }
 public class TestData2 {
   private String email;
   private String body;
 }

and in jsp page:

     <form ng-submit="add(ab)">
           <input type="text" ng-model="ab.name">   
           <input type="text" ng-model="ab.data[0].email">  
           <input type="text" ng-model="ab.dat[0].body">  
     </form>  

and in Angularjs controller:

  app.controller('myController', function ($scope, $http) {
    $scope.ab = {};
    $scope.addComment = function(ab) {
        console.log(ab);
        $http.post('/add', ab).success(function(response){}
    )};