模型Result

public class Result {

  private String msg;
  
  private List module;

  public String getMsg() {
    return msg;
  }

  public void setMsg(String msg) {
    this.msg = msg;
  }

  public List getModule() {
    return module;
  }

  public void setModule(List module) {
    this.module = module;
  }  
}

为什么要使用泛型, 可以理解泛型可以接受任意类型, 有些代码是公用的, 如结果集, 不可能为每个具体结果定义一个模型, 比如 Result、Result等。

public class User {

  private Long user_id;

  private String user_name;

  public User() {

  }

  public User(Long userId, String name) {
    this.user_id = userId;
    this.user_name = name;
  }

  public Long getUser_id() {
    return user_id;
  }

  public void setUser_id(Long user_id) {
    this.user_id = user_id;
  }

  public String getUser_name() {
    return user_name;
  }

  public void setUser_name(String user_name) {
    this.user_name = user_name;
  }
}

下面直接看下泛型的转换 

  public static void main(String[] args) {
    
    Result r = new Result();
    
    r.setMsg("msg");
    
    List users = new ArrayList<>();
    users.add(new User(1L, "hehe"));
    users.add(new User(2L, "haha"));
    
    r.setModule(users);
    
    String js = JSON.toJSONString(r);
    
    System.out.println(js);
    
    Result obj = (Result)JSON.parseObject(js, Result.class);
    
    User user = obj.getModule().get(0);
    System.out.println(user);
  }

结果 ：

{"module":[{"user_id":1,"user_name":"hehe"},{"user_id":2,"user_name":"haha"}],"msg":"msg"}

Exception in thread "main" java.lang.ClassCastException: com.alibaba.fastjson.JSONObject cannot be cast to com.yuanmeng.json.User

 at com.yuanmeng.json.fanxing.Client.main(Client.java:32)

采用fastjson框架的 TypeReference 即可将json串转成定义好的泛型对象

Result obj = (Result) JSON.parseObject(js, new TypeReference>(){});