jsp ajax获取不到response.getwriter传回的值

下面先贴出的Servlet.java中的部分代码
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("utf-8");
boolean flag = selectUserList(request, response);
if(flag){
try {

                String username = request.getParameter("username");
                String password = request.getParameter("password1");
                String phone = request.getParameter("phone");
                Connection conn = JdbcUtil.getConnection();
                String sql = "insert into t_user values(null,'" + username +
                        "','" + password + "','" + phone + "')";
                System.out.println(sql);
                JdbcUtil.executeUpdate(conn, sql);
                response.getWriter().write("{\"result\":\"成功\"}");
                return ;
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
}


然后是jsp文件中ajax的代码
$.ajax({
                    url:"RegisterServlet",
                    data:{
                        username:$(".main_username").val(),
                        phone:$(".main_phone").val(),
                        password1:$(".main_password1").val(),
                        password2:$(".main_password2").val()
                    },
                    type:"post",
                    dataType:"json",

                    success:function(data){

                        if(data.result == "成功"){

                            location.href="https://www.baidu.com";
                        }
                    },
                    error:function(){
                    }
                });

                为什么获取不到传回来的result的值呢？求大神帮忙解答一下 谢谢

在网上找到类似的问题，已经解决了，虽然不知道为什么。。
$(".main_button").click(function(){
if(i1 == 1 && i2 == 1 && i3 == 1 && i4 == 1)
{
var flag = ""; //新增一个变量
$.ajax({
url:"RegisterServlet",
data:{
username:$(".main_username").val(),
phone:$(".main_phone").val(),
password1:$(".main_password1").val(),
password2:$(".main_password2").val()
},
type:"post",
dataType:"json",

                    success:function(data){
                        flag = data.result;           //用变量获取传回来的值
                        alert(flag);                     //获取成功了
                        if(flag == "success"){

                            location.href="agreement.html";
                        }
                    },
                    error:function(){
                    }
                });
            }
            else
                alert("输入有误，请重新输入！");

        });

走断点看看你的json串，一步步看