我经历了很多答案，并且在Google上搜索了很多，但仍然找不到为什么我的帖子请求不起作用的原因。

这是我的jsp：

<div class="container">
      <form class="form-signin" ng-controller="MyController">
        <h2 class="form-signin-heading">Please sign in</h2>
        <label for="username" class="sr-only">Username</label>
        <input type="text" id="username"  ng-model="user.name" class="form-control" placeholder="Username" required autofocus>
        <label for="password" class="sr-only">Password</label>
        <input type="password" ng-model="user.password" id="password" class="form-control" placeholder="Password" required>
        <button class="btn btn-lg btn-primary btn-block" ng-click="login()" type="submit">Sign in</button>
      </form>
    </div>

这是我的控制器：

app.controller('MyController', function($scope, $http) {

    $scope.login = function() {
        console.log($scope.user);
        $http({
            method : 'POST',
            url : 'login',
            data : $scope.user,
            headers: {
                'Content-Type': 'application/json'
            }
        }).success(function(data) {
            console.log(data);
        }).error(function(data) {
            console.log(data);
        });
        console.log("POST done");
    };
});

而我的servlet：

protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        System.out.println("inside do POST");
        Gson gson = new Gson();
        JsonParser parser = new JsonParser();
        JsonObject obj = (JsonObject) parser
                .parse(request.getParameter("data"));
        Iterator it = (Iterator) obj.entrySet();
        while (it.hasNext()) {
            System.out.println(it.next());
        }
        System.out.println("over");
    }

我不断收到此Null指针异常

java.lang.NullPointerException
    at java.io.StringReader.<init>(StringReader.java:50)
    at com.google.gson.JsonParser.parse(JsonParser.java:45)
    at com.zookeeperUI.controller.Login.doPost(Login.java:40)

请告诉我我这里做错了什么。