【实用】Java对象与JSON字符串的互转，实用操作！

最近，工作中会涉及到Java对象与JSON字符串相互转换，虽然说并不难，但打算还是梳理一番，主要内容有：

• JSON 字符串 转 普通对象
• 普通对象 转 JSON 字符串
• JSON 字符串数组 转 List 集合对象
• List 集合对象 转 JSON 字符串数组
• JSON 字符串 转 装有对象的 Map
• 装有对象的Map 转 JSON 字符串

开始之前，需要在 pom.xml 引入相关的 jar 包：

<!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.16.10</version>
    <scope>provided</scope>
</dependency>
<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.75</version>
</dependency>

接着，创建一个普通对象，使用 lombok 提供的注解：

@Data
public class ExtInfo {
    private String orderId;
    private String creatTime;
    private String postion;
    private String orderType;
    private String amount;
}

测试1：json字符串 与 普通对象 互转

public class Demo {
    @Test
    void test1() {
        //  json字符串转普通对象
        String jsonStr = "{\"orderId\":\"1111\",\"creatTime\":\"20210817223001\",\"postion\":\"hangZhou xiXi\",\"orderType\":\"4\",\"amount\":\"20\"}";
        JSONObject jsonObject = JSONObject.parseObject(jsonStr);
        ExtInfo extInfo = JSONObject.toJavaObject(jsonObject, ExtInfo.class);
        System.out.println(extInfo);
        System.out.println(extInfo.getOrderId());
        
        // 普通对象转json字符串
        String str = JSONObject.toJSONString(extInfo);
        System.out.println(str);
    }
}

测试结果：

ExtInfo(orderId=1111, creatTime=20210817223001, postion=hangZhou xiXi, orderType=4, amount=20)
1111
{"amount":"20","creatTime":"20210817223001","orderId":"1111","orderType":"4","postion":"hangZhou xiXi"}

测试2：json字符串数组 与 List集合对象 互转

public class Demo2 {
    @Test
    void test2() {  
        // json字符串数组转对象List集合
        String jsonStrArray = "[{\"orderId\":\"1111\",\"creatTime\":\"20210817223001\",\"postion\":\"hangZhou xiXi\",\"orderType\":\"4\",\"amount\":\"20\"}]";
        JSONArray jsonArray = JSONObject.parseArray(jsonStrArray);
        // 方式一、根据索引获取 JSONArray 中的对象
        ExtInfo extInfo1 = jsonArray.getObject(0, ExtInfo.class);
        System.out.println(extInfo1);
        // 方式二、转成List,再从List获取对象
        List extInfos = jsonArray.toJavaList(ExtInfo.class);
        ExtInfo extInfo2 =  extInfos.get(0);
        System.out.println(extInfo2);
 
        //  List集合对象转json字符串数组
        String strs = JSONObject.toJSONString(extInfos);
        System.out.println(strs);
    }
}

测试结果：

ExtInfo(orderId=1111, creatTime=20210817223001, postion=hangZhou xiXi, orderType=4, amount=20)
ExtInfo(orderId=1111, creatTime=20210817223001, postion=hangZhou xiXi, orderType=4, amount=20)
[{"amount":"20","creatTime":"20210817223001","orderId":"1111","orderType":"4","postion":"hangZhou xiXi"}]

测试3：json字符串 与 装有对象的Map 互转

public class Demo3 {
    @Test
    void test3() {  
        // map格式转对象
        String mapJsonStr = "{\"level\":{\"orderId\":\"1111\",\"creatTime\":\"20210817223001\",\"postion\":\"hangZhou xiXi\",\"orderType\":\"4\",\"amount\":\"20\"}}";
        Map extInfoMap = JSONObject.parseObject(
                mapJsonStr,
                new TypeReference>() {});
        System.out.println(extInfoMap);
        System.out.println(extInfoMap.get("level"));
        // 对象转map格式
        String mapStr = JSONObject.toJSONString(extInfoMap);
        System.out.println(mapStr);
    }
}

测试结果：

{level=ExtInfo(orderId=1111, creatTime=20210817223001, postion=hangZhou xiXi, orderType=4, amount=20)}
ExtInfo(orderId=1111, creatTime=20210817223001, postion=hangZhou xiXi, orderType=4, amount=20)
{"level":{"amount":"20","creatTime":"20210817223001","orderId":"1111","orderType":"4","postion":"hangZhou xiXi"}}