jQuery Ajax Post 回调函数不执行怎么办

$.post('${pageContext.request.contextPath}/user_deleteUser',{uid:row.uid},function(result){
                            if (result.errorMsg){
                                $.messager.show({    
                                    title: 'Error',
                                    msg: result.errorMsg
                                });
                            } else {
                                $('#dg').datagrid('reload');    
                            }
                        },'json');

public String deleteUser() {
        int count = userDao.deleteUser(model.getUid());
        try {
            PrintWriter writer = response.getWriter();
            if(count<=0) writer.write("{'errorMsg':'删除失败'}");
            else writer.write("{'success':'删除成功'}");
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

我的：{'hello':'world'}
标准：{"hello":"world"}

{\"hello\":\"world\"}