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Data exchange JSON

2022-07-01 03:19:00 【Al_ tair】

JSON

- Data exchange JSON

Hello, everyone , I'm Xiao Sheng , The following is my study of data exchange -JSON Learning notes of

Data exchange JSON

summary

json Online document

JSON refer to JavaScript Object notation , It is also a lightweight text data exchange format

JSON The definition format of

var  Variable name  = {
     
    "k1" : value, // Number  type  
    "k2" : "value", //  String type 
    "k3" : [], //  An array type  
    "k4" : {
    }, // json  object type  
    "k5" : [{
    },{
    }] // json  Array  
};

Code example

<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="UTF-8">
		<title>json  Quick start case </title>
		<script type="text/javascript"> var myJson = {
       "key1": " Niansheng ", //  character string   "key2": 123, // Number  "key3": [1, "hello", 2.3], //  Array   "key4": {
      "age": 12, "name": "jack"}, //json  object   "key5": [ //json  Array   {
      "k1": 10, "k2": "tom"}, {
      "k3": 30, "k4": "smith"} ] , }; //  visit  json  Properties of   console.log("key1= " + myJson.key1); //  Niansheng  console.log("key1= " + myJson.key2); // 123 //  visit  json  Array properties for   console.log("key3[1]= " + myJson.key3[1]); // hello //  visit  key4  Of  name  attribute   console.log("name= " , myJson.key4); // name= {age: 12, name: 'jack'} console.log("name= " + myJson.key4); // name= [object Object] console.log("name= " + myJson.key4.name); // jack //  visit  key5 json  The first element of the array   console.log("myJson.key5[0]= " + myJson.key5[0]); //[object, object]  console.log("myJson.key5[0].k2= " + myJson.key5[0].k2) // tom </script>
	</head>
	<body>
		<h1>json  Quick start case </h1>
	</body>
</html>

JSON Object and string object conversion

JSON.stringify(json) function : Will a json Object converted to json character string
JSON.parse( jsonString ) function : Will a json String conversion to json object

Code example

<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="UTF-8">
		<title>JSON  Object and string object conversion </title>
		<script type="text/javascript"> //JSON  It's a  build-in  object , Built-in objects  console.log(JSON) // json  object   var jsonObj = {
      "name": " Niansheng ","age": 18}; console.log("json  object  " , jsonObj); //  hold  json  Object is converted to a string object   var jsonStr = JSON.stringify(jsonObj); console.log(" character string : " + jsonStr); //  hold  json  Object's string , Convert into  json  object   var jsonObj2 = JSON.parse(jsonStr); console.log("json  object  " , jsonObj2); </script>
	</head>
	<body>
		<h1>JSON  Object and string object conversion </h1>
	</body>
</html>

Attention to detail

In defining Json Object time , key Value can be used ’ ’ perhaps " " Representation string , Even without quotes
- var json_person = {“name”: “jack”, “age”: 100};
- var json_person = {‘name’: ’jack‘, ‘age’: 100};
- var json_person = {name: “jack”, age: 100};
But convert the native string to json Object time , You have to use “”, Otherwise, an error will be reported
```
var str = "{\"name\": \" Niansheng \",\"age\": 18}"
console.log("json  object  " , JSON.parse(str)); 
```
JSON.springify(json object ) String returned , All are “” String represented , Yes, it can be converted into json object

JSON stay java Use in

java Use in json, Packages that need to be introduced gson.jar
Gson yes Google What is provided is used in Java Objects and JSON Mapping between data Java Class library
JSON character string and Java Objects are converted to each other

Javabean Objects and json character string Transformation

JavaBean

public class Book {
    
    private Integer id;
    private String name;

    public Book() {
    
    }

    public Book(Integer id, String name) {
    
        this.id = id;
        this.name = name;
    }

    public Integer getId() {
    
        return id;
    }

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

    public String getName() {
    
        return name;
    }

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

    @Override
    public String toString() {
    
        return "Book{" +
                "id=" + id +
                ", name='" + name + '\'' +
                '}';
    }
}

public class JavaJson {
    
    public static void main(String[] args) {
    
        // Gson  yes  Google  What is provided is used in  Java  Objects and  JSON  Mapping between data  Java  Class library 
        Gson gson = new Gson();
        //  establish javabean object 
        Book book = new Book(1, " A dream of red mansions ");
        // Javabean  object  => json  character string 
        String s = gson.toJson(book);
        System.out.println(s); // {"id":1,"name":" A dream of red mansions "}
        // json  character string  => Javabean  object 
        String str = "{\"id\": 2 , \"name\" : \" Water margin \" }";
        Book book2 = gson.fromJson(str, Book.class);
        System.out.println(book2); // Book{id=2, name=' Water margin '}
    }
}

List Objects and json character string Transformation

public class LIstJson {
    
    public static void main(String[] args) {
    
        Gson gson = new Gson();
        // List  Objects and  json  character string   Transformation 
        List<Book> list = new ArrayList<>();
        //  add to 4 This book 
        list.add(new Book(1," A dream of red mansions "));
        list.add(new Book(2," The romance of The Three Kingdoms "));
        list.add(new Book(3," Water margin "));
        list.add(new Book(4," Journey to the west "));

        // List  object  => json  character string 
        String s = gson.toJson(list);
        System.out.println(s);

        // json  character string  => List  object 
        String listBook = "[{\"id\":1,\"name\":\" A dream of red mansions \"},{\"id\":2,\"name\":\" The romance of The Three Kingdoms \"}," +
            "{\"id\":3,\"name\":\" Water margin \"},{\"id\":4,\"name\":\" Journey to the west \"}]";
        // TypeToken  Is a custom generic class , When creating a , You need to specify a specific type , Here we designate as  List<Book>
        // type:java.util.List<com.al_tair.Book>
        //  establish TypeToken<List<Book>>(){} Anonymous inner class , The default call is... In the parameterless constructor super Constructors , To access protected TypeToken Constructors 
        Type type = new TypeToken<List<Book>>(){
    }.getType();
        List<Book> listJson = gson.fromJson(listBook, type);
        System.out.println(listJson);
    }
}

map Objects and json character string Transformation

public class MapJson {
    
    public static void main(String[] args) {
    
        Gson gson = new Gson();
        // Map  Objects and  json  character string   Transformation 
        Map<Integer,Book> map = new HashMap();
        //  add to 4 This book 
        map.put(1,new Book(1," A dream of red mansions "));
        map.put(2,new Book(2," The romance of The Three Kingdoms "));
        map.put(3,new Book(3," Water margin "));
        map.put(4,new Book(4," Journey to the west "));

        // Map  object  => json  character string 
        String s = gson.toJson(map);
        System.out.println(s);

        // json  character string  => Map  object 
        String mapBook = "{\"1\":{\"id\":1,\"name\":\" A dream of red mansions \"},\"2\":{\"id\":" +
            "2,\"name\":\" The romance of The Three Kingdoms \"},\"3\":{\"id\":3,\"name\":\" Water margin \"},\"4\":{\"id\":4,\"name\":\" Journey to the west \"}}";

        Type type = new TypeToken<Map<Integer, Book>>() {
    }.getType();
        Map<Integer,Book> bookMap = gson.fromJson(mapBook, type);
        System.out.println(bookMap);
    }
}