java-course

JSON

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What is JSON?

JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy for humans to read and write and easy for machines to parse and generate. JSON is based on a subset of the JavaScript programming language, but is completely language-independent and can be used with virtually any programming software.

JSON is commonly used to serialize and transmit structured data over a network, particularly in web programming between client and server applications.

JSON Structure

JSON is built on two structures:

1. A collection of key/value pairs (often called an “object” in other languages). In JSON, this is represented by curly braces { ... }.
2. An ordered list of values (often called an “array” in other languages). In JSON, this is represented by square brackets [ ... ].

JSON Example

{
  "name": "John Doe",
  "age": 30,
  "isEmployee": true,
  "addresses": [
    {"street": "123 Main St", "city": "Anytown"},
    {"street": "456 Maple St", "city": "Hometown"}
  ]
}

Working with JSON in Java

In Java, there are various libraries available for working with JSON. The most popular ones are Jackson and Google Gson. Here’s how you can work with these libraries:

Using Gson

To work with Gson, first, add the dependency to your project. If you’re using Maven, add the following to your pom.xml:

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.8.6</version>
</dependency>

Example of serialization and deserialization with Gson:

import com.google.gson.Gson;

public class Main {
    public static void main(String[] args) {
        Gson gson = new Gson();

        // Serialization
        User user = new User("John Doe", 30);
        String json = gson.toJson(user);
        System.out.println(json);

        // Deserialization
        User userFromJson = gson.fromJson(json, User.class);
        System.out.println(userFromJson.getName());
    }
}

class User {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

Using Jackson

To use Jackson, add the following dependencies to your pom.xml:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.8</version>
</dependency>

Example of serialization and deserialization with Jackson:

import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {
    public static void main(String[] args) throws Exception {
        ObjectMapper mapper = new ObjectMapper();

        // Serialization
        User user = new User("John Doe", 30);
        String json = mapper.writeValueAsString(user);
        System.out.println(json);

        // Deserialization
        User userFromJson = mapper.readValue(json, User.class);
        System.out.println(userFromJson.getName());
    }
}

class User {
    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }
}

Both libraries provide a simple and convenient API for serializing objects into JSON and deserializing JSON back into Java objects. The choice between Gson and Jackson depends on personal preference and specific project requirements.