基于Jackson的ObjectMapper类进行json字符串与对象之间的互相转换

清疚 2022-05-14 23:58 510阅读 0赞

## 问题 ##

jackson是Java开源领域声名赫赫的json字符串操作类库，与fastjson等齐名。本文将给出示例，如何来快速进行json string和对象之间的互相转换。

## 代码示例 ##

Profile数据对象类：

@Data
    public class Profile { 
        private String id;
    
        //Flag active profile on default
        private boolean activeByDefault;
    
        //all the user defined properties
        private Map<String, String> properties = new HashMap<>();
    }

测试代码：

@Log4j2
    public class JsonUtilTest { 
        private ObjectMapper objectMapper = new ObjectMapper();
        @Before
        public void setUp() throws Exception {
        }
    
        @After
        public void tearDown() throws Exception {
        }
    
        @Test
        public void test() throws IOException {
            List<Profile> profiles = new ArrayList<Profile>();
    
            Profile profile = new Profile();
            profile.setId("dev");
            profile.setActiveByDefault(true);
            Map<String, String> props = new HashMap<>();
            props.put("key.val1", "testval1");
            props.put("key.val2", "testval2");
            profile.setProperties(props);
            profiles.add(profile);
    
            Profile profile1 = new Profile();
            profile1.setId("test");
            profile1.setActiveByDefault(false);
            Map<String, String> props1 = new HashMap<>();
            props1.put("key.val3", "testval3");
            props1.put("key.val4", "testval4");
            profile1.setProperties(props1);
            profiles.add(profile1);
    
            String jsonStr = objectMapper.writeValueAsString(profiles);
            log.debug("Json String:" + jsonStr);
            List<Profile> newProfiles = objectMapper.readValue(jsonStr, TypeFactory.defaultInstance().constructCollectionType(List.class, Profile.class));
    
            log.debug("profiles:" + Arrays.toString(newProfiles.toArray()));
        }
    }

测试结果的输出：

10:28:26.323 [main] DEBUG com.jd.ai.code.robot.metadata.JsonUtilTest - Json String:[{
       "id":"dev","activeByDefault":true,"properties":{
       "key.val1":"testval1","key.val2":"testval2"}},{
       "id":"test","activeByDefault":false,"properties":{
       "key.val3":"testval3","key.val4":"testval4"}}]
    10:28:26.359 [main] DEBUG com.jd.ai.code.robot.metadata.JsonUtilTest - profiles:[Profile(id=dev, activeByDefault=true, properties={key.val1=testval1, key.val2=testval2}), Profile(id=test, activeByDefault=false, properties={key.val3=testval3, key.val4=testval4})]

另外一种实现方式：

List<Profile> newProfiles = objectMapper.readValue(jsonStr, new TypeReference<List<Profile>>(){});

## 总结 ##

能够在一行之内能够解决的问题，一般都是相对比较简单的……