Customizing Spring Boot's ObjectMapper for Date Formatting and JSON Conversion

Spring Boot initializes ObjectMapper

Spring Boot’s auto‑configuration class JacksonAutoConfiguration contains a nested static configuration that creates a bean named jacksonObjectMapper when Jackson2ObjectMapperBuilder is on the classpath and no other ObjectMapper bean is defined.

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(Jackson2ObjectMapperBuilder.class)
static class JacksonObjectMapperConfiguration {
    @Bean
    @Primary
    @ConditionalOnMissingBean
    ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
        return builder.createXmlMapper(false).build();
    }
}

If you provide your own ObjectMapper bean, this auto‑configuration is skipped.

Custom date formatting

Define a configuration class that creates an ObjectMapper with a SimpleDateFormat of "yyyy-MM-dd hh:mm:ss". The mapper will format Date fields such as createDate in the User class accordingly.

public class User {
    private String userNo;
    private String username;
    private int age;
    private Date createDate;
    // getters and setters omitted
}

@Configuration
public class JacksonConfig {
    @Bean
    public ObjectMapper jacksonObjectMapper() {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd hh:mm:ss"));
        return mapper;
    }
}

Running a unit test shows the JSON output:

{"userNo":"1000","username":"Tom","age":18,"createDate":"2019-12-31 05:15:30"}

Using the ObjectMapper directly

Inject the auto‑configured ObjectMapper into a controller and call writeValueAsString to serialize a User instance.

@RestController
public class JsonController {
    @Autowired
    private ObjectMapper objectMapper;

    @GetMapping("writeString")
    public String writeString() throws JsonProcessingException {
        User user = new User();
        user.setUserNo("1000");
        user.setUsername("Tom");
        user.setAge(18);
        user.setCreateDate(new Date());
        return objectMapper.writeValueAsString(user);
    }
}

For deserialization you can bind JSON to a POJO or read it as a JsonNode tree.

@PostMapping("readJson")
public void readJson(String userJson) throws JsonProcessingException {
    User user = objectMapper.readValue(userJson, User.class);
    System.out.println("userNo: " + user.getUserNo());
    // ... other fields

    JsonNode jsonNode = objectMapper.readTree(userJson);
    JsonNode userNo = jsonNode.get("userNo");
    System.out.println("userNo(from JsonNode): " + userNo.textValue());
}

Unit‑test snippets demonstrate both endpoints.

Source code is available at https://github.com/secbr/springboot-all/tree/master/springboot-json.