1.jackson

导包：

<!-- jackson -->
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.10.0</version>
</dependency>

使用

public static void main(String[] args) {
        Map<String, Object> map = new HashMap<>();
        map.put("a",1000);
        map.put("b",2000);
        ObjectMapper mapper = new ObjectMapper();
        try {
            // map 转 json 字符串
            String s = mapper.writeValueAsString(map);
            System.out.println(s);
            // json 字符串 转 map
            Map map1 = mapper.readValue(s, Map.class);
            System.out.println(map1);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
}

2.fastjson

导包：

<!-- fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.62</version>
</dependency>

使用

public static void main(String[] args) {
        Map<String, Object> map = new HashMap<>();
        map.put("a",1000);
        map.put("b",2000);
        // map 转 json 字符串
        String s = JSONObject.toJSONString(map);
        System.out.println(s);
        // json 字符串 转 map
        Map<String,Object> obj = JSON.parseObject(s, Map.class);
        System.out.println(obj);

        System.out.println("----------------------");

        // list 转 json 字符串
        String s1 = JSON.toJSONString(map);
        System.out.println(s1);
        // json 字符串 转 list
        List<String> strings = JSON.parseArray(s1, String.class);
        System.out.println(strings);

        // List<Map<String,Object>>
        List<Map<String, Object>> listMap = JSON.parseObject(jsonString, new TypeReference<List<Map<String,Object>>>(){});
}

ok了。