在序列化用alibaba的json包把物件進行序列化的時候，總是報錯

Exception in thread "main" com.alibaba.fastjson.JSONException: default constructor not found. class com.mex.test.redis.Person

Person類

public class Person {

    private String name;
    private int age;



    public Person(String name, int age) {
        this
 
.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

User類

public class User {

    private String id;
    private List<Person> users = new ArrayList<Person>();


    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public List<Person> getUsers() {
        return users;
    }

    public
 
 void setUsers(List<Person> users) {
        this.users = users;
    }
}

測試類

public class SerializationTest {

    public static void main(String[] args) {

        User user = new User();
        user.setId("1001");
        Person p1 = new Person("xiaoming",23);
        Person p2 = new Person("jack",34);
        ArrayList<Person> pList = Lists.newArrayList();
        pList.add(p1);
        pList.add(p2);

        user.setUsers(pList);

        // 序列化
        String s = JSON.toJSONString(user);
        System.out.println(s);

        User user1 = JSON.parseObject(s, User.class);
        System.out.println(user1);
    }
}

查找了半天的資料，fastJson在反序列化的時候需要呼叫物件的預設構造方法，如果該物件之中還包含其他的物件，那麼都需要建立預設的無參構造方法。

解決方案：將User的預設無參構造和Person的預設無參構造補充到類中，即可。

public User() {
    }

public Person() {
    }

打印出來的資訊為：

{"id":"1001","users":[{"age":23,"name":"xiaoming"},{"age":34,"name":"jack"}]}
com.mex.test.redis.User@15f550a

Process finished with exit code 0