java使用json

July 22, 2022

JSON-java 库

https://mvnrepository.com/artifact/org.json/json
https://github.com/stleary/JSON-java

一个轻量级的 json 库

安装

xml

<dependency>
  <groupId>org.json</groupId>
  <artifactId>json</artifactId>
  <version>20220320</version>
  <type>bundle</type>
</dependency>

使用

java

import org.json.*;
public class Main {
    public static void main(String[] args) {
        JSONObject jsonObj = new JSONObject();
        jsonObj.put("name", "练习生");
        jsonObj.put("time", 0);
        jsonObj.put("time", 2.5); // 后面的覆盖前面
        jsonObj.put("hobbies", new String[]{"唱", "跳", "RAP", "篮球"});
        jsonObj.append("bool", true); // 添加为数组元素

        JSONArray jsonArr = jsonObj.getJSONArray("bool");
        jsonArr.put(false); // 数组追加元素

        System.out.println(jsonObj.toString()); // => {...json}
        System.out.println(jsonArr.getBoolean(0)); // => true
        System.out.println(jsonObj.get("bool")); // get 方法返回object
        if (!jsonObj.isNull("name")) System.out.println(jsonObj.getString("name"));
        if (!jsonObj.isNull("time")) System.out.println(jsonObj.getDouble("time"));
    }
}

{"bool":[true,false],"hobbies":["唱","跳","RAP","篮球"],"name":"练习生","time":2.5}
true
[true,false]
练习生
2.5

API 演示

java

import org.json.*;
import java.util.*;
public class Main {
    public static void main(String[] args) {
        /* 建造者模式 */
        JSONStringer stringer = new JSONStringer();
        stringer.object().key("k").value("v").key("number").value(1).endObject();
        System.out.println(stringer); // => {"k":"v","number":1}

        /* 编码数组，集合 */
        var aa = new JSONArray(new int[]{1, 2, 3});
        var ll = new JSONArray(List.of(4, 5, 6));
        var ss = new JSONArray(Set.of(7, 8, 9)); // 输出顺序随机
        System.out.println(aa); // => [1,2,3]
        System.out.println(ll); // => [4,5,6]
        System.out.println(ss); // => [7,9,8]

        /* 编码哈希表 */
        var mm = new JSONObject(Map.of("k1", "v1", "k2", "v2"));
        System.out.println(mm); // => {"k1":"v1","k2":"v2"}

        /* 解码json */
        JSONTokener token = new JSONTokener("[{\"key1\":\"value1\"},{\"key2\":\"value2\"}]");
        JSONArray ja = new JSONArray(token);
        System.out.println(ja.get(0)); // => {"key1":"value1"}
    }
}

Gson

安装

xml

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.9.0</version>
</dependency>

使用

java

import com.google.gson.*;
import com.google.gson.reflect.*;

import java.util.*;

public class Main {
    public static void main(String[] args) throws Throwable {
        GsonBuilder builder = new GsonBuilder();
        builder.setPrettyPrinting();
        Gson gson = builder.create();
        // or simply:
        // Gson gson = new Gson();

        // 反序列化为JavaBean
        Student student = gson.fromJson("{\"name\":\"Max\", \"age\":24}", Student.class);
        System.out.println(student);

        // 反序列化数组
        String[] sa = gson.fromJson("[\"a\",\"b\",\"c\"]", String[].class);
        System.out.println(sa);

        // 反序列化其它
        List<String> sl = gson.fromJson("[\"a\",\"b\",\"c\"]", new TypeToken<List<String>>() {
        }.getType());
        System.out.println(sl);

        // 从Reader中获取
        // Reader r = new BufferedReader(new FileReader("student.json"));
        // Student stu = gson.fromJson(r, Student.class);


        // 序列化为JSON
        String json = gson.toJson(student);
        System.out.println(json);

        // 直接编码JSON
        System.out.println(gson.toJson(new int[]{1, 2, 3}));
        System.out.println(gson.toJson(List.of(4, 5, 6)));
        System.out.println(gson.toJson("json-string"));
        System.out.println(gson.toJson(2022));
        System.out.println(gson.toJson(Map.of("k1", "v1", "k2", "v2")));
    }
}

class Student {
    private String name;
    private int 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;
    }

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

输出

Student{name='Max', age=24}
[Ljava.lang.String;@4f47d241
[a, b, c]
{
  "name": "Max",
  "age": 24
}
[
  1,
  2,
  3
]
[
  4,
  5,
  6
]
"json-string"
2022
{
  "k1": "v1",
  "k2": "v2"
}

注解演示

java

import com.google.gson.*;
import com.google.gson.annotations.*;

public class Main {
    public static void main(String[] args) throws Throwable {
        GsonBuilder builder = new GsonBuilder();
        builder.excludeFieldsWithoutExposeAnnotation(); // 排除没有Expose注解的字段
        Gson gson = builder.create();

        Student student = new Student();
        student.setName("Jvav");
        student.setAge(20);
        student.setId(202212345678L);
        System.out.println(gson.toJson(student)); // => {"student_name":"Jvav"}
    }
}

class Student {
    // 序列化时，更名为student_name
    // 反序列化时，从student_name获取，或从alternate指定的数组中给定的键名获取
    @SerializedName(value = "student_name", alternate = {"NAME", "name"})
    // 参与序列化，也参与反序列化
    @Expose(serialize = true, deserialize = true)
    private String name;

    // 设置了 excludeFieldsWithoutExposeAnnotation，但没有 Expose 注解，忽略此字段
    private int age;

    // 使用 transient 关键字，无需配置即可指定忽略此字段
    private transient long id;

    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 long getId() {
        return id;
    }

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

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