1、依赖的包
非常有用的参考：
（1）json在线转换器：http://json.parser.online.fr/
（2）json介绍：http://www.json.org/json-zh.html
2、普通JavaBean
（1）基本JavaBean
public class User {
private String username;
private String password;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
}（2）转化成JSONArray
User user = new User();
user.setUsername("lp");
user.setPassword("1234");
JSONArray json = JSONArray.fromObject(user);
System.out.println(json);
//结果：[{"password":"1234","username":"lp"}]
（3）转化成JSONObject
User user = new User();
user.setUsername("lp");
user.setPassword("1234");
JSONObject json = JSONObject.fromObject(user);
System.out.println(json);
//结果;{"password":"1234","username":"lp"}
3、List<User>
（1）转化成JSONArray
List<User>users = new ArrayList<>();
User user = new User();
user.setUsername("lp");
user.setPassword("1234");
User userSecond = new User();
userSecond.setUsername("ch");
userSecond.setPassword("4567");
users.add(user);
users.add(userSecond);
JSONArray json = JSONArray.fromObject(users);
System.out.println(json);
//结果：[{"password":"1234","username":"lp"},{"password":"4567","username":"ch"}]
（2）转化成JSONObject
不可以直接通过JSONObject jsonObj = JSONObject.fromObject(users);进行
可以通过如下方式：
JSONObject json = new JSONObject();
json.put("users", users);
json.put("userSecond", userSecond);
System.out.println(json);
//结果：{"users":[{"password":"1234","username":"lp"},{"password":"4567","username":"ch"}],"userSecond":{"password":"4567","username":"ch"}}
4、Map
（1）转化成JSONArray
Map<String, Object>map = new HashMap<String, Object>();
map.put("users", users);
map.put("user", user);
JSONArray json = JSONArray.fromObject(map);
System.out.println(json);
//结果：[{"users":[{"password":"1234","username":"lp"},{"password":"4567","username":"ch"}],"user":{"password":"1234","username":"lp"}}]
（2）转化成JSONObject
Map<String, Object>map = new HashMap<String, Object>();
map.put("users", users);
map.put("user", user);
JSONObject json = JSONObject.fromObject(map);
System.out.println(json);
//结果：{"users":[{"password":"1234","username":"lp"},{"password":"4567","username":"ch"}],"user":{"password":"1234","username":"lp"}}