List<Person> list = new ArrayList<Person>();
  list.add(new Person("张三","123"));
  list.add(new Person("张2三","sdf"));
  list.add(new Person("张3三","fd"));
  JSONArray json1 = JSONArray.fromObject(list);  
       System.out.println(json1.toString());




Person pe = new Person("李四","lal");

  JSONObject json3 = JSONObject.fromObject(pe);

  System.out.println(json3.toString());




JSONArray.fromObject可以将list或者list<T>直接转换为JSON
JSONObject.fromObjec可以将一个对象直接转换为JSON