JSONObject详解(com.alibaba)-fastjson2

前言

fastjson2 是 FASTJSON 项目的重要升级，目标是为下一个十年提供一个高性能的JSON库， fastjson2 性能相比原先旧的 fastjson 有了很大提升,并且 fastjson2 更安全，完全删除autoType白名单，提升了安全性。

关于fastjson2升级指南

fastjson2 的github地址

一、导入fastjson2依赖

maven如下：

pom(本文所有代码仅使用这一个依赖即可):

  

    
        
            com.alibaba.fastjson2
            fastjson2
            2.0.26
        
    

需要注意的一点是在使用 fastjson2 时导入的包名是 com.alibaba.fastjson2 ，就像下面这样：

import com.alibaba.fastjson2.JSON;

import com.alibaba.fastjson2.JSONObject;

import com.alibaba.fastjson2.JSONArray;

二、json对象与json数组的创建

json对象创建

import com.alibaba.fastjson2.JSONObject;

public class Demo {
    public static void main(String[] args) {
        JSONObject info = new JSONObject();
        info.put("name", "张三");
        info.put("age", "18");
        info.put("地理", "70");
        info.put("英语", "60");

        System.out.println(info);
    }
}

json数组创建

import com.alibaba.fastjson2.JSONArray;

public class Demo {
    public static void main(String[] args) {
        JSONArray array = new JSONArray();
        array.add("1班");
        array.add("2班");
        array.add("3班");

        System.out.println(array);
    }
}

import com.alibaba.fastjson2.JSONArray;
import com.alibaba.fastjson2.JSONObject;

public class Demo {
    public static void main(String[] args) {
        JSONObject info1 = new JSONObject();
        info1.put("name", "张三");
        info1.put("age", "18");
        JSONObject info2 = new JSONObject();
        info2.put("name", "李四");
        info2.put("age", "19");

        //把上面创建的两个json对象加入到json数组里
        JSONArray array = new JSONArray();
        array.add(info1);
        array.add(info2);

        System.out.println(array);
    }
}

三、json对象取值与json数组遍历取值

json对象取值

import com.alibaba.fastjson2.JSONArray;
import com.alibaba.fastjson2.JSONObject;

public class Demo {
    public static void main(String[] args) {
        JSONArray array = new JSONArray();
        array.add("1班");
        array.add("2班");
        array.add("3班");
        JSONObject school = new JSONObject();
        school.put("schoolName", "第一中学");
        school.put("teacher", "刘梅");

        JSONObject info = new JSONObject();
        info.put("name", "张三");
        info.put("age", "18");
        info.put("gradle", array);
        info.put("schoolInfo", school);

        //从info中取值
        System.out.println(info.getString("name")); //张三
        System.out.println(info.getIntValue("age"));//18
        System.out.println(info.getJSONArray("gradle"));//["1班","2班","3班"]
        System.out.println(info.getJSONObject("schoolInfo"));//{"schoolName":"第一中学","teacher":"刘梅"}
    }
}

json数组遍历取值

import com.alibaba.fastjson2.JSONArray;
import com.alibaba.fastjson2.JSONObject;

public class Demo {
    public static void main(String[] args) {
        JSONObject info1 = new JSONObject();
        info1.put("name", "张三");
        info1.put("age", "18");
        JSONObject info2 = new JSONObject();
        info2.put("name", "李四");
        info2.put("age", "19");

        JSONArray array = new JSONArray();
        array.add(info1);
        array.add(info2);
        //遍历获取json数组中对象的值
        for (int i = 0; i < array.size(); i++) {
            JSONObject json = array.getJSONObject(i);
            System.out.println(json.getString("name"));
            System.out.println(json.getString("age"));
        }
    }
}

四、json对象与字符串的转换

json对象与字符串的转换

import com.alibaba.fastjson2.JSON;
import com.alibaba.fastjson2.JSONObject;

public class Demo {
    public static void main(String[] args) {
        JSONObject info = new JSONObject();
        info.put("name", "张三");
        info.put("age", "18");
        info.put("地理", "70");
        info.put("英语", "60");

        //JSON对象转字符串
        String str = JSON.toJSONString(info);
        System.out.println(str);
        //JSON字符串转JSON对象
        JSONObject json = JSONObject.parseObject(str);
        System.out.println(json);
    }
}

json字符串的字节数组转json对象

import com.alibaba.fastjson2.JSON;
import com.alibaba.fastjson2.JSONObject;

public class Demo {
    public static void main(String[] args) {
        String str = "{\"name\":\"张三\",\"age\":\"18\",\"地理\":\"70\",\"英语\":\"60\"}";

        byte[] bytes = str.getBytes();
        JSONObject data = JSON.parseObject(bytes);

        System.out.println(data);
    }
}

五、json数组与字符串的转换

import com.alibaba.fastjson2.JSON;
import com.alibaba.fastjson2.JSONArray;

public class Demo {
    public static void main(String[] args) {
        String text = "[\"张三\",\"李四\",\"王五\"]";
        System.out.println(text);

        //json字符串转json数组
        JSONArray data = JSON.parseArray(text);
        //json数组转json字符串
        String str = JSONArray.toJSONString(data);

        System.out.println(data);
        System.out.println(str);
    }
}

六、json字符串转java对象的转换

Student类如下：

public class Student {
    public String name;
    public 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;
    }

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

json字符串转java对象的转换

import com.alibaba.fastjson2.JSON;

public class Demo {
    public static void main(String[] args) {
        Student student = new Student("张三", 18);

        //Student对象转JSON字符串
        String studentStr = JSON.toJSONString(student);
        //JSON字符串转Student对象
        Student data = JSON.parseObject(studentStr, Student.class);

        System.out.println(studentStr);
    }
}

java对象转byte数组转换

import com.alibaba.fastjson2.JSON;

public class Demo {
    public static void main(String[] args) {
        Student student = new Student("张三", 18);

        //Student对象转字节数组
        byte[] text = JSON.toJSONBytes(student);
        //字节数组转Student对象
        Student data = JSON.parseObject(text, Student.class);

        System.out.println(data.getName() + data.getAge());
    }
}

七、json字符串与Map转换

json字符串转Map

import com.alibaba.fastjson2.JSONObject;
import com.alibaba.fastjson2.TypeReference;

import java.util.Map;

public class Demo {
    public static void main(String[] args) {
        String str = "{\n" +
                "\"gradle\":\"高一\",\n" +
                "\"number\":\"2\",\n" +
                "\"people\":[{\"name\":\"张三\",\"age\":\"15\",\"phone\":\"123456\"},\n" +
                "         {\"name\":\"李四\",\"age\":\"16\",\"phone\":\"78945\"}]\n" +
                "}";

        //json字符串转Map
        Map map = JSONObject.parseObject(str, new TypeReference>() {
        });
        System.out.println(map.get("gradle").toString());
        System.out.println(map.get("number").toString());
        System.out.println(map.get("people").toString());

    }
}

Map转json字符串

(注意：如果直接使用JSON.toJSONString(map)转换，因为"测试1"的值为null，转换的结果就会是 {“测试2”:“hello”})

import com.alibaba.fastjson2.JSON;
import com.alibaba.fastjson2.JSONWriter;

import java.util.HashMap;
import java.util.Map;

public class Demo {
    public static void main(String[] args) {
        Map map = new HashMap<>();
        map.put("测试1", null);
        map.put("测试2", "hello");

        //{"测试2":"hello","测试1":null}
        String str = JSON.toJSONString(map, JSONWriter.Feature.WriteMapNullValue);

        System.out.println(str);
    }
}

如果你使用的是老的fastjson1(下述是简单示例，不可使用),可以像下面这样转换：

     

Map map = new HashMap<>();
map.put("测试1", null);
map.put("测试2", "hello");
String str = JSON.toJSONString(map, SerializerFeature.WriteMapNullValue) ;

八、json数组转List

import com.alibaba.fastjson2.JSONArray;
import com.alibaba.fastjson2.JSONObject;

import java.util.List;
import java.util.Map;

public class Demo {
    public static void main(String[] args) {
        String str = "{\n" +
                "\"gradle\":\"高一\",\n" +
                "\"number\":\"2\",\n" +
                "\"people\":[{\"name\":\"张三\",\"age\":\"15\",\"phone\":\"123456\"},\n" +
                "         {\"name\":\"李四\",\"age\":\"16\",\"phone\":\"78945\"}]\n" +
                "}";

        JSONObject strJson = JSONObject.parseObject(str);
        //获取people数组
        JSONArray people = strJson.getJSONArray("people");
        //json数组转List
        List

如果你使用的是老的fastjson1,可以像下面这样转换：       

String str = "{\n" +

                "\"gradle\":\"高一\",\n" +

                "\"number\":\"2\",\n" +

                "\"people\":[{\"name\":\"张三\",\"age\":\"15\",\"phone\":\"123456\"},\n" +

                "         {\"name\":\"李四\",\"age\":\"16\",\"phone\":\"78945\"}]\n" +

                "}";

JSONObject strJson = JSONObject.parseObject(str);//字符串转json对象
String people = String.valueOf(strJson.getJSONArray("people"));
List> list = (List>) JSONArray.parse(people);