如何从 REST 控制器端点返回 LocalDateTime？

Question

I'm writing a REST controller in Spring- java, and one of my endpoints should return a LocalDateTime variable.

@GetMapping(path = "/lastDateTimeOfReset")
LocalDateTime fetchLastDateTimeOfReset() {
   return mongoManagerService.fetchLastDateTimeOfReset();
}

This is the client request:

ResponseEntity<LocalDateTime> lastDateEntity = restTemplate.getForEntity(url, LocalDateTime.class);

I get the following excepation on my client side:

org.springframework.web.client.RestClientException: 
Error while extracting response for type [class java.time.LocalDateTime] and content type [application/json;charset=UTF-8]; 
nested exception is org.springframework.http.converter.HttpMessageNotReadableException: 
JSON parse error: Expected array or string.; 
nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Expected array or string.
at [Source: (PushbackInputStream); line: 1, column: 1]

I checked the return value on debug mode and it is a valid LocalDateTime. Why is this exception thrown and how to overcome it?

Answer 1

You can use String to overcome this issue.

@GetMapping(path = "/lastDateTimeOfReset")
String fetchLastDateTimeOfReset() {
   return (mongoManagerService.fetchLastDateTimeOfReset()).toString();
}

Client Request:

ResponseEntity<String> lastDateEntity = restTemplate.getForEntity(url, String.class);

Answer 2

You need to check return type of mongoManagerService.fetchLastDateTimeOfReset();

Or Test your application with below sample code

Service

@GetMapping(path = "/lastDateTimeOfReset")
    LocalDateTime fetchLastDateTimeOfReset() {
       return LocalDateTime.now();
    }

Client

RestTemplate rs = new RestTemplate();
ResponseEntity<LocalDateTime> lastDateEntity = rs.getForEntity(new URI("http://localhost:8089/lastDateTimeOfReset"), LocalDateTime.class);
System.out.println(lastDateEntity);

Output

<200,2020-02-19T15:00:51.603220,[Content-Type:"application/json;charset=UTF-8", Transfer-Encoding:"chunked", Date:"Wed, 19 Feb 2020 09:30:51 GMT"]>

Answer 3

Problem solved! In general- I should've added this configuration to my app:

@Configuration
public class MvcConfig {    
    @Configuration
    @EnableWebMvc
    public class MessageConvertersConfiguration implements WebMvcConfigurer {
        @Override
        public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
            converters.add(new MappingJackson2HttpMessageConverter(objectMapper()));
        }

        @Bean
        public ObjectMapper objectMapper() {
            DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("dd-MM-yyyy'T'HH:mm:ss");
            SimpleModule localDateModule = new SimpleModule();
            localDateModule.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(dateTimeFormatter));
            localDateModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(dateTimeFormatter));

            ObjectMapper mapper = new ObjectMapper();
            mapper.registerModules(localDateModule);

            return mapper;
        }
    }
}

* IMPORTANT!!! - In Tests add this to your rest template: *

restTemplate.setMessageConverters(Collections.singletonList(new MappingJackson2HttpMessageConverter(objectMapper())));