Use the Gson library to convert the map key values in Java to the structure object to Json_java

Map's storage-structured key/value form, Key and value can be ordinary types, can also be written by themselves JavaBean (this article), can also be a list with generics.

(Gson GitHub project page: Https://github.com/google/gson)

JavaBean

In this case you want to focus on the definition of how to revert json to a normal JavaBean object when TypeToken.

Entity classes:

public class Point { 
  private int x; 
  private int y; 
 
  public point (int x, int y) { 
    this.x = x; 
    This.y = y; 
  } 
 
  public int GetX () {return 
    x; 
  } 
 
  public void SetX (int x) { 
    this.x = x; 
  } 
 
  public int GetY () {return 
    y; 
  } 
 
  public void sety (int y) { 
    this.y = y; 
  } 
 
  @Override public 
  String toString () {return 
    "point [x=" + x + ", y=" + y + "]"; 
  } 
 
} 

Test class:

Import Java.util.LinkedHashMap; 
 
Import Java.util.Map; 
Import Com.google.gson.Gson; 
Import Com.google.gson.GsonBuilder; 
 
Import Com.google.gson.reflect.TypeToken; public class GsonTest3 {public static void main (string[] args) {Gson Gson = new Gsonbuilder (). Enablecomplexmap 
 
    Keyserialization (). Create (); Map<point, string> map1 = new Linkedhashmap<point, string> ();//Use Linkedhashmap to arrange the results in FIFO order Map1.put (new 
    Point (5, 6), "a"); 
    Map1.put (New Point (8, 8), "B"); 
    String s = Gson.tojson (MAP1); System.out.println (s);//Result: [[{"X": 5, "Y": 6}, "a"],[{"X": 8, "Y": 8}, "B"]] map<point, string> retmap = Gson.fromjs 
    On (S, New Typetoken<map<point, string>> () {}.gettype ()); 
    For (Point P:retmap.keyset ()) {System.out.println ("key:" + P + "values:" + Retmap.get (p)); 
 
    } System.out.println (Retmap); 
    System.out.println ("----------------------------------"); Map<string, Point> map2 = new linkedhashmap<string, point> (); 
    Map2.put ("A", New Point (3, 4)); 
    Map2.put ("B", New Point (5, 6)); 
    String s2 = Gson.tojson (MAP2); 
 
    SYSTEM.OUT.PRINTLN (S2); map<string, point> retMap2 = Gson.fromjson (s2, New typetoken<map<string, point>> () {} 
    . GetType ()); 
    For (String Key:retMap2.keySet ()) {System.out.println ("key:" + key + "values:" + retmap2.get (key)); 

 } 
 
  } 
}

Results:

[[{"X": 5, "Y": 6}, "a"],[{"X": 8, "Y": 8}, "B"]] 
Key:point [X=5, y=6] values:a 
key:point [X=8, y=8] values:b 
{point [X=5, Y=6]=a, point [X=8, y=8]=b} 
-------- -------------------------- 
{"A": {"X": 3, "Y": 4}, "B": {"X": 5, "Y": 6}} 
key:a values:point [x=3, y=4] 
key:b Values:point [X=5, y=6] 

Generic List

Entity classes:

Import Java.util.Date; 
  public class Student {private int id; 
  private String name; 
 
  Private Date birthday; 
  public int getId () {return id; 
  The public void setId (int id) {this.id = ID; 
  Public String GetName () {return name; 
  public void SetName (String name) {this.name = name; 
  Public Date Getbirthday () {return birthday; 
  The public void Setbirthday (Date birthday) {this.birthday = birthday; 
        @Override public String toString () {return "Student [birthday= + birthday +", id= "+ ID +", name= " 
  + name + "]"; 
 
  } public class Teacher {private int id; 
 
  private String name; 
 
  Private String title; 
  public int getId () {return id; 
  The public void setId (int id) {this.id = ID; 
  Public String GetName () {return name; 
  public void SetName (String name) {this.name = name; Public String GetTitle () {RETUrn title; 
  public void Settitle (String title) {this.title = title; 
        @Override public String toString () {return "Teacher [id= + ID +", name= "+ name +", title= "+ title 
  + "]"; 

 } 
 
}

Test class:

Package com.tgb.lk.demo.gson.test4; 
Import java.util.ArrayList; 
Import Java.util.Date; 
Import Java.util.LinkedHashMap; 
Import java.util.List; 
 
Import Java.util.Map; 
Import Com.google.gson.Gson; 
 
Import Com.google.gson.reflect.TypeToken; 
    public class GsonTest4 {public static void main (string[] args) {Student student1 = new Student (); 
    Student1.setid (1); 
    Student1.setname ("Li Kun"); 
 
    Student1.setbirthday (New Date ()); 
    Student Student2 = new Student (); 
    Student2.setid (2); 
    Student2.setname ("Cao Guisheng"); 
 
    Student2.setbirthday (New Date ()); 
    Student Student3 = new Student (); 
    Student3.setid (3); 
    Student3.setname ("Liupo"); 
 
    Student3.setbirthday (New Date ()); 
    list<student> stulist = new arraylist<student> (); 
    Stulist.add (STUDENT1); 
    Stulist.add (Student2); 
 
    Stulist.add (STUDENT3); 
    Teacher teacher1 = new Teacher (); 
    Teacher1.setid (1); 
    Teacher1.setname ("rice teacher"); 
 
  Teacher1.settitle ("Professor");  Teacher teacher2 = new Teacher (); 
    Teacher2.setid (2); 
    Teacher2.setname ("Teacher Ding"); 
    Teacher2.settitle ("lecturer"); 
    list<teacher> teacherlist = new arraylist<teacher> (); 
    Teacherlist.add (Teacher1); 
 
    Teacherlist.add (TEACHER2); 
    map<string, object> map = new linkedhashmap<string, object> (); 
    Map.put ("Students", stulist); 
 
    Map.put ("Teachers", teacherlist); 
    Gson Gson = new Gson (); 
    String s = Gson.tojson (map); 
 
    System.out.println (s); 
 
    System.out.println ("----------------------------------"); map<string, object> retmap = Gson.fromjson (S, New typetoken<map<string, list<object>>> () 
 
    {}.gettype ()); 
      For (String Key:retMap.keySet ()) {System.out.println ("key:" + key + "values:" + retmap.get (key)); 
        if (Key.equals ("students")) {list<student> stulist = (list<student>) retmap.get (key); 
      System.out.println (stulist); } else if (key.equals ("Teachers")) {list<teacher> tchrlist = (list<teacher>) retmap.get (key); 
      System.out.println (tchrlist); 

 } 
    } 
 
  } 
}

Output results:

{"Students": [{"id": 1, "name": "Li Kun", "Birthday": "June, 9:48:19 PM"},{"id": 2, "name": "Cao Guisheng", "Birthday": "June 22, 2012 9:48:19 pm "},{" ID: 3, "name": "Liupo", "Birthday": "June, 9:48:19 PM"}], "Teachers": [{"id": 1, "name": "M Teacher", "title": " Professor "},{" ID ": 2," name ":" Teacher Ding "," title ":" Lecturer "}]} 
---------------------------------- 
key:students values:[{id= 1.0, Name= Li Kun, Birthday=jun, 9:48:19 pm}, {id=2.0, name= Cao Gui-sheng, Birthday=jun, 9:48:19 pm}, {id=3.0, name= Liupo, b Irthday=jun 9:48:19 pm}] 
[{id=1.0, name= Li Kun, Birthday=jun, 9:48:19 PM}, {id=2.0, name= Cao Gui, Birthday=ju N, 9:48:19 pm}, {id=3.0, name= Liupo, Birthday=jun, 9:48:19 PM}] 
key:teachers values:[{id=1.0, name= rice teacher, t Professor Itle=}, {id=2.0, name= Teacher, title= Lecturer}] 
[{id=1.0, name= rice teacher, Professor Title=}, {id=2.0, name=, teacher, title= lecturer}]