Android : 序列化 JSON简单应用

1. JSON介绍

JSON(JavaScript Object Notation)是一种轻量级的数据交换格式,易于阅读和写入,同时也易于机器解析和生成。它基于JavaScript的子集,采用完全独立于语言的文本格式来存储和表示数据。JSON是纯文本,并且完全是语言无关的。

JSON使用JavaScript语法来描述数据结构,但实际上JSON所用的数据结构都是诸如对象、数组、键/值对等的常见数据结构。

* 对象是由键/值对组成的集合,使用大括号 `{}` 表示。
* 数组是由一组值组成的集合,使用方括号 `[]` 表示。

例如:


```json
{
  "name": "张三",
  "age": 30,
  "isStudent": false,
  "subjects": ["数学", "英语", "历史"]
}
```
在这个例子中,我们有一个对象,包含四个键/值对。其中,"name" 的值为 "张三","age" 的值为 30,"isStudent" 的值为 false。最后一个键是 "subjects",其值是一个数组,包含三个字符串元素。

JSON的主要优点是它的简洁性和可读性。在JSON中,对象由花括号 `{}` 包围,而数组由方括号 `[]` 包围。此外,JSON支持多种数据类型,包括字符串、数字、布尔值、null、数组和对象。这使得JSON成为一种非常灵活的数据格式,可以用来表示各种复杂的数据结构。

2. 简单使用

1 .导框架 Gson

Maven 存储库:com.google.code.gson » gson (mvnrepository.com)

dependencies {

    // https://mvnrepository.com/artifact/com.google.code.gson/gson
    implementation("com.google.code.gson:gson:2.10.1")

}

2 .Student.java

package com.example.json;


public class Student {

    // 不要某个属性序列化 transient
//   private transient String name;

    //序列化时自定义名字 把 name 改成 user_name
//    @SerializedName("user_name")
//    private String name;

    private String name;
    private int age;
    private Score score;

    public Student(String name, int age, Score score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

    public Score getScore() {
        return score;
    }

    public void setScore(Score score) {
        this.score = score;
    }

}

3. Score.java

package com.example.json;

public class Score {
    private float math;
    private float english;
    private float chinese;
    private String grade;

    public Score(float math, float english, float chinese) {
        this.math = math;
        this.english = english;
        this.chinese = chinese;
        if (math >= 90 && english >= 90 && chinese >= 90) {
            this.grade = "A";
        } else if (math >= 80 && english >= 80 && chinese >= 80) {
            this.grade = "B";
        } else {
            this.grade = "C";
        }
    }

    public float getMath() {
        return math;
    }

    public void setMath(float math) {
        this.math = math;
    }

    public float getEnglish() {
        return english;
    }

    public void setEnglish(float english) {
        this.english = english;
    }

    public float getChinese() {
        return chinese;
    }

    public void setChinese(float chinese) {
        this.chinese = chinese;
    }

    public String getGrade() {
        return grade;
    }

    public void setGrade(String grade) {
        this.grade = grade;
    }
}

4.MainActivity.java

package com.example.json;

import android.os.Bundle;
import android.util.Log;
import androidx.appcompat.app.AppCompatActivity;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        try {

            //JSONObject 生成Json 数据
            JSONObject jsonObject = new JSONObject();
            jsonObject.put("name", "jack");
            jsonObject.put("age", 19);
            String json = jsonObject.toString(); //{"name":"jack","age":19}
            Log.e("JSON", "Json 数据:" + json.toString());

            //JSONObject 解析 Json 数据
            String data = "{ name:\"jack\", age: 19 }";
            JSONObject js = new JSONObject(data);
            String name = (String) js.get("name");
            Integer age = (Integer) js.get("age");
            Log.e("JSON", "解析 Json 数据---name:" + name + "---age:" + age);

            //Gson  对象 生成json数据
            Student student = new Student("jack", 25, new Score(60, 60, 60));
            String json2 = new Gson().toJson(student);
            //{"age":25,"name":"jack","score":{"chinese":60.0,"english":60.0,"grade":"C","math":60.0}}
            Log.e("JSON", "Json 数据:" + json2);

            //Gson  解析json数据 生成对象
            String data2 = "{\"age\":25,\"name\":\"jack\",\"score\":{\"chinese\":60.0,\"english\":60.0,\"grade\":\"C\",\"math\":60.0}}";
            Student student2 = new Gson().fromJson(data2, Student.class);
            Log.e("JSON", "Json student2 数据:" + student2);

            //Gson  数组对象 生成json数据
            Student student3 = new Student("jack", 25, new Score(90, 90, 90));
            Student student4 = new Student("Tom", 24, new Score(80, 80, 80));
            Student[] students = new Student[]{student3, student4};
            String json3 = new Gson().toJson(students);
            //[{"age":25,"name":"jack","score":{"chinese":90.0,"english":90.0,"grade":"A","math":90.0}},
            // {"age":24,"name":"Tom","score":{"chinese":80.0,"english":80.0,"grade":"B","math":80.0}}]
            Log.e("JSON", "Json 数据:" + json3);

            //  Gson  解析json数据 数组对象
            String data3 = "[{\"age\":25,\"name\":\"jack\",\"score\":{\"chinese\":90.0,\"english\":90.0,\"grade\":\"A\",\"math\":90.0}}," +
                    "{\"age\":24,\"name\":\"Tom\",\"score\":{\"chinese\":80.0,\"english\":80.0,\"grade\":\"B\",\"math\":80.0}}]";
            Student[] students2 = new Gson().fromJson(data3, Student[].class);
            Log.e("JSON", "Json 数据:" + students2);

            //Gson  List 对象 生成json数据
            List studentList = new ArrayList<>();
            studentList.add(new Student("jack", 25, new Score(90, 90, 90)));
            studentList.add(new Student("Tom", 24, new Score(80, 80, 80)));
            String json4 = new Gson().toJson(studentList);
            //[{"age":25,"name":"jack","score":{"chinese":90.0,"english":90.0,"grade":"A","math":90.0}},
            // {"age":24,"name":"Tom","score":{"chinese":80.0,"english":80.0,"grade":"B","math":80.0}}]
            Log.e("JSON", "Json 数据:" + json4);


            //Gson  解析json数据  生成 List 对象
            String data4 = "[{\"age\":25,\"name\":\"jack\",\"score\":{\"chinese\":90.0,\"english\":90.0,\"grade\":\"A\",\"math\":90.0}}," +
                    "{\"age\":24,\"name\":\"Tom\",\"score\":{\"chinese\":80.0,\"english\":80.0,\"grade\":\"B\",\"math\":80.0}}]";
            List students3 = new Gson().fromJson(data4, new TypeToken>() {
            }.getType());
            Log.e("JSON", "Json 数据:" + students3);

        } catch (JSONException e) {
            throw new RuntimeException(e);
        }
    }
}

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