Android实战：使用fastjson解析JSON数据

一、 fastjson简介

fastjson是一个Java语言编写的高性能和通用的JSON序列化和反序列化类库，在阿里巴巴经济体的大力推动下成长为了业内流行的JSON库，具有反序列化飞速、易用性强、准确性高、兼容性好、灵活度高的特点。

Json是一种轻量级的数据交换格式，它具有可读性强、数据格式简洁等特点，被广泛应用于网页开发、移动应用、Web API等场合。fastjson就是Java语言下用于解析json字符串的类库，它提供了丰富的API，可以帮助开发人员轻松解析json字符串。

二、快速入门

1、新建Android项目并在build.gradle文件中添加fastjson库的引用

dependencies {
    implementation 'com.alibaba:fastjson:1.2.80'
}

2、在MainActivity.java文件中添加如下代码

import android.os.Bundle;
import android.util.Log;

import androidx.appcompat.app.AppCompatActivity;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {
    private String jsonStr;

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

        jsonStr = "{\n" +
                "    \"name\": \"Tom\",\n" +
                "    \"age\": 21,\n" +
                "    \"score\": {\n" +
                "        \"math\": 90,\n" +
                "        \"english\": 87\n" +
                "    },\n" +
                "    \"hobby\": [\n" +
                "        \"study\",\n" +
                "        \"write\",\n" +
                "        \"run\"\n" +
                "    ]\n" +
                "}";
        //将Json字符串转换为Java对象
        Student student = JSON.parseObject(jsonStr, Student.class);
        Log.i("MainActivity", "name=" + student.getName());
        Log.i("MainActivity", "age=" + student.getAge());

        //获取Json对象
        JSONObject jsonObject = JSON.parseObject(jsonStr);
        int mathScore = jsonObject.getJSONObject("score").getIntValue("math");
        Log.i("MainActivity", "mathScore=" + mathScore);

        //获取Json数组
        JSONArray jsonArray = jsonObject.getJSONArray("hobby");
        for (int i = 0; i < jsonArray.size(); i++) {
            String hobby = jsonArray.get(i).toString();
            Log.i("MainActivity", "hobby=" + hobby);
        }

        //将Java对象转换为Json字符串
        Student newStudent = new Student("Bob", 23);
        String newJsonStr = JSON.toJSONString(newStudent);
        Log.i("MainActivity", "newJsonStr=" + newJsonStr);
    }
}

3、新建Student.java文件并定义如下Java Bean类

public class Student {
    private String name;
    private int age;

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

    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;
    }
}

4、运行程序并查看输出结果，效果如下

name=Tom
age=21
mathScore=90
hobby=study
hobby=write
hobby=run
newJsonStr={"age":23,"name":"Bob"}

三、常用API介绍

1、将Json字符串转换为Java对象

 String jsonStr = "{\"name\":\"Tom\", \"age\":21}";
 Student student = JSON.parseObject(jsonStr, Student.class);

2、将Java对象转换为Json字符串

Teacher teacher = new Teacher("Lily", 35);
String jsonStr = JSON.toJSONString(teacher);
Log.i(TAG, jsonStr);

3、获取JsonObject对象

String jsonStr = "{\"name\":\"Tom\", \"age\":21}";
JSONObject jsonObject = JSON.parseObject(jsonStr);
String name = jsonObject.getString("name");
int age = jsonObject.getIntValue("age");

4、获取JsonArray数组

String jsonStr = "[{\"name\":\"Tom\", \"age\":21},{\"name\":\"Jerry\", \"age\":23}]";
JSONArray jsonArray = JSON.parseArray(jsonStr);
for (int i = 0; i < jsonArray.size(); i++) {
    JSONObject jsonObject = jsonArray.getJSONObject(i);
    String name = jsonObject.getString("name");
    int age = jsonObject.getIntValue("age");
    Log.i(TAG, "name=" + name + ", age=" + age);
}

5、序列化和反序列化null对象

// 将null转化为JSON字符串
String nullJson = JSON.toJSONString(null);
Log.i(TAG, "nullJson=" + nullJson); //null

// 将null值的JSON字符串转化为Object对象
Object nullObject = JSON.parse(nullJson);
Log.i(TAG, "nullObject=" + nullObject); //null

// 将Java对象序列化为JSON字符串
Student student = null;
String studentJson = JSON.toJSONString(student, SerializerFeature.WriteNullStringAsEmpty);
Log.i(TAG, "studentJson=" + studentJson); //{"name":"","age":0,null:null}

// 将JSON字符串反序列化为Java对象
Student newStudent = JSON.parseObject(studentJson, Student.class);
Log.i(TAG, "newStudent.getName()=" + newStudent.getName()); //""
Log.i(TAG, "newStudent.getAge()=" + newStudent.getAge()); //0
Log.i(TAG, "newStudent.getInfo()=" + newStudent.getInfo()); //null

四、使用技巧

1、解析复杂Json对象

String jsonStr = "{\n" +
        "  \"error\": 0,\n" +
        "  \"reason\": \"成功\",\n" +
        "  \"result\": {\n" +
        "    \"stat\": \"1\",\n" +
        "    \"list\": [\n" +
        "      {\n" +
        "        \"stationno\": \"1\",\n" +
        "        \"content\": \"好孩子\"\n" +
        "      },\n" +
        "      {\n" +
        "        \"stationno\": \"2\",\n" +
        "        \"content\": \"天才\"\n" +
        "      }\n" +
        "    ]\n" +
        "  }\n" +
        "}";
JSONObject jsonObject = JSON.parseObject(jsonStr);
JSONObject result = jsonObject.getJSONObject("result");
JSONArray jsonArray = result.getJSONArray("list");
List<Station> stationList = new ArrayList<>();
for (int i = 0; i < jsonArray.size(); i++) {
    JSONObject obj = jsonArray.getJSONObject(i);
    Station station = JSON.toJavaObject(obj, Station.class);
    stationList.add(station);
}
Log.i(TAG, stationList.toString());

2、序列化和反序列化不同类型的对象

String jsonStr = "{\"name\":\"Tom\",\"value\":50}";
Object obj = JSON.parse(jsonStr);
if (obj instanceof Map) { //反序列化为Map对象
    Map<String, Object> map = (Map<String, Object>) obj;
    Log.i(TAG, map.get("name").toString() + "-" + map.get("value").toString());
} else if (obj instanceof MyObject) { //反序列化为Java对象
    MyObject myObject = (MyObject) obj;
    Log.i(TAG, myObject.getName() + "-" + myObject.getValue().toString());
}

MyObject myObject = new MyObject("John", 30);
String jsonText = JSON.toJSONString(myObject);
Log.i(TAG, jsonText); //{"content":["John",30]}

MyObject myObject2 = JSON.parseObject(jsonText, MyObject.class);
Log.i(TAG, myObject2.getName() + "-" +myObject2.getValue().toString());

五、总结

fastjson是Android开发中解析json数据的利器。我们通过上述内容的学习，可以将json字符串快速转化成Java对象，结合快速入门中的示例，使你可以无缝的将Json格式数据序列化和反序列化。

如果你想要更深入了解fastjson库的功能和用法，还可以查看官方文档，用最好的工具解析最好的数据。