JSON parsing

JSON: JavaScript Object Notation

JSON is a simple spectrum of JS objects and a lightweight data exchange format

A subset of the JS specification developed by the European Computer Association, which is completely independent of the programming language and uses text to represent data

Object format

Describe the above contents with java, js, XML and JSON:

a copy of books
 title
 brief introduction

java

class Book{
	private String name;
	private String info;
	get/set...
}

	Book b = new Book();
	b.setName("Java core technology ");
	b.setInfo("Told Java Relevant contents of core technology");
...

js

You can create objects directly without writing classes
Use the object directly Property name to create the property of the object

var b = new Object();
b.name = "Java core technology ";
b.info = "Told Java Relevant contents of core technology"	;

XML

<book>
	<name>Java core technology </name>
	<info>Told Java Relevant contents of core technology</info>
</book>

JSON

The quotation marks of name and info in JS can be omitted, either single or double. When interacting with Java programmers, name and info are quoted

{
	"name":"Java core technology ",
	"info":"Told Java Relevant contents of core technology"
}

A pair of braces represents an object, and braces contain key value pairs

The attribute of the object is described by key value pairs. The attribute name and attribute value are separated by colons: attribute name: attribute value

The key of the key value pair should be enclosed in quotation marks (JS can be parsed correctly, but usually when Java parses, the key will report an error without quotation marks)

The value of a key value pair can be any type of data in JS

Multiple attributes are separated by commas

In JSON format, it can be nested with objects: [element 1, element 2...]

Java and JSON

Quickly convert objects in Java into JSON format strings

Convert a string in JSON format into a Java object

GSON

From Google

Convert object to JSON string

step

1. Introduce JAR package

2. Write the following code where the JSON string needs to be converted:
   String json = new Gson(). Tojson (object to be converted);

Code example:

public static void main(String[] args) {
    //1. Create a Gson object
    Gson g = new Gson();
    //2. Conversion
    Book book = new Book(100,"Java core technology ","Told Java Relevant contents of core technology");
    String s = g.toJson(book);//The incoming object is converted to the corresponding Json object
    System.out.println(s);
}

Execution result:

{"id":100,"name":"Java core technology ","info":"Told Java Relevant contents of core technology"}

Convert JSON strings to objects

step

1. Introduce JAR package
2. Write the following code where Java objects need to be converted:
   Object = new gson() Fromjason (JSON string, object type. class);

Code example 1 (back to object):

public static void main(String[] args) {
    //1. Create a Gson object
    Gson g = new Gson();
    //2. Conversion {"id":100,"name":"Java core technology", "info": "about Java core technology"}
    Book book = g.fromJson("{\"id\":100,\"name\":\"Java core technology \",\"info\":\"Told Java Relevant contents of core technology\"}", Book.class);
    System.out.println(book.getId());
    System.out.println(book.getName());
    System.out.println(book.getInfo());
}

Execution result:

100
Java core technology 
Told Java Relevant contents of core technology

Code example 2 (roll back set):

public static void main(String[] args) {
    //1. Create a Gson object
    Gson g = new Gson();
    //2. Conversion {"id":100,"name":"Java core technology", "info": "describes the relevant contents of Java core technology", "page": ["encapsulation", "inheritance", "polymorphism]}
    HashMap data = g.fromJson("{\"id\":100,\"name\":\"Java core technology \",\"info\":\"Told Java Relevant contents of core technology\",\"page\":[\"encapsulation\",\"inherit\",\"polymorphic\"]}", HashMap.class);
    System.out.println(data.get("id"));
    System.out.println(data.get("name"));
    System.out.println(data.get("info"));
    System.out.println(data.get("page"));
    System.out.println(data.get("page").getClass());
    List page = (List)data.get("page");
    System.out.println(page.get(1));
}

Execution result:

The array part of the object is converted to ArrayList during the conversion process

100.0
Java core technology 
Told Java Relevant contents of core technology
[encapsulation, inherit, polymorphic]
class java.util.ArrayList
 inherit

FastJson

From Ali

Convert object to JSON string

step

1. Introduce JAR package
2. Write the following code where the JSON string needs to be converted:
   String json=JSON. Tojsonstring (object to be converted);

Code example:

public static void main(String[] args) {
    Book book = new Book(100,"Java core technology ","Told Java Relevant contents of core technology");
    //1. Conversion
    String s = JSON.toJSONString(book);
    System.out.println(s);
}

Execution result:

{"id":100,"info":"Told Java Relevant contents of core technology","name":"Java core technology "}

Convert JSON strings to objects

step

1. Introduce JAR package
2. Where Java objects need to be converted, write the following code:
   Type object name = JSON Parseobject (JSON string, type. class);
   or
   List < type > List = JSON Parsearray (JSON string, type. class);

Code example 1 (back to object):

public static void main(String[] args) {
    //1. Conversion {"id":100,"info": "about Java core technology", "name":"Java core technology"}
    Book book = JSON.parseObject("{\"id\":100,\"info\":\"Told Java Relevant contents of core technology\",\"name\":\"Java core technology \"}", Book.class);
    System.out.println(book.getId());
    System.out.println(book.getName());
    System.out.println(book.getInfo());
}

Execution result:

100
Java core technology 
Told Java Relevant contents of core technology

Code example 2 (roll back set):

public static void main(String[] args) {
    //1. Conversion ["encapsulation", "inheritance", "polymorphism"]
    List<String> strings = JSON.parseArray("[\"encapsulation\",\"inherit\",\"polymorphic\"]", String.class);
    System.out.println(strings.get(1));
}

Execution result:

inherit