java对象转json字符串

         //创建一个对象
         BeanJpushExtra jpushExtra = new BeanJpushExtra();
                ("用户A");
                ("设备A");
                ("分享内容A");

          // java 对象转 json字符串
           json = new ();
          String jpushObjec= (jpushExtra).toString();

          //打印出结果
          (jpushObjec);

结果：

{
   "shareMsg":"分享内容A",
   "shareDevice":"设备A",
   "shareUser":"用户A"
}