feign request return value deserialization LocalDateTime exception record

Preface

Recently, the project team used feign to call remote services, and the consumer reported the following exception

From the exception information, it can be concluded that the localdatime deserialization has an exception, and this exception is caused by Jackson's inability to handle it. So we can adapt it to Jackson's ObjectMapper

Solution

1. Introduce in pom.xml

    <dependency>
                <groupId>com.fasterxml.jackson.datatype</groupId>
                <artifactId>jackson-datatype-jsr310</artifactId>
                <version>${jackson.version}</version>
            </dependency>

            <dependency>
                <groupId>com.fasterxml.jackson.datatype</groupId>
                <artifactId>jackson-datatype-jdk8</artifactId>
                <version>${jackson.version}</version>
            </dependency>

Note: jackson-datatype-jsr310 This is the time used to support the jsr310 specification, jackson-datatype-jdk8 is used to support new JDK8-specific types, such as Optional

2. Replace the default ObjectMapper

@Configuration
public class LocalDateTimeConfig  {

    public static final String DEFAULT_DATE_TIME_FORMAT = "yyyy-MM-dd HH:mm:ss";


  
    @Bean
    public ObjectMapper objectMapper() {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.registerModule(new Jdk8Module());
        objectMapper.setDateFormat(new SimpleDateFormat(DEFAULT_DATE_TIME_FORMAT));
        objectMapper.setTimeZone(TimeZone.getTimeZone("GMT+8"));
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        objectMapper.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE);
        JavaTimeModule javaTimeModule = new JavaTimeModule();
        javaTimeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
        javaTimeModule.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
        objectMapper.registerModule(javaTimeModule).registerModule(new ParameterNamesModule());
        return objectMapper;
    }

Question: Why can feign handle LocalDateTime after replacing the default ObjectMapper

The answer is

@Configuration(proxyBeanMethods = false)
public class FeignClientsConfiguration {

    @Autowired
    private ObjectFactory<HttpMessageConverters> messageConverters;


    @Bean
    @ConditionalOnMissingBean
    public Decoder feignDecoder() {
        return new OptionalDecoder(
                new ResponseEntityDecoder(new SpringDecoder(this.messageConverters)));
    }
}

The default converter of messageConverters is based on HttpMessageConvertersAutoConfiguration.

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass(HttpMessageConverter.class)
@Conditional(NotReactiveWebApplicationCondition.class)
@AutoConfigureAfter({ GsonAutoConfiguration.class, JacksonAutoConfiguration.class, JsonbAutoConfiguration.class })
@Import({ JacksonHttpMessageConvertersConfiguration.class, GsonHttpMessageConvertersConfiguration.class,
        JsonbHttpMessageConvertersConfiguration.class })
public class HttpMessageConvertersAutoConfiguration {

    static final String PREFERRED_MAPPER_PROPERTY = "spring.http.converters.preferred-json-mapper";

    @Bean
    @ConditionalOnMissingBean
    public HttpMessageConverters messageConverters(ObjectProvider<HttpMessageConverter<?>> converters) {
        return new HttpMessageConverters(converters.orderedStream().collect(Collectors.toList()));
    }

ObjectProvider has the function of lazy loading and will be loaded according to the actual situation. The springboot web module will introduce Jackson related packages by default. There is such a paragraph on the official website

This means that the default HttpMessageConverter is MappingJackson2HttpMessageConverter, and MappingJackson2HttpMessageConverter will use objectMapper to serialize and deserialize

The above words are organized as follows with code

 public static final String DEFAULT_DATE_TIME_FORMAT = "yyyy-MM-dd HH:mm:ss";


    @Bean
    public Decoder feignDecoder() {
        return new ResponseEntityDecoder(new SpringDecoder(messageConverters()));
    }

    public ObjectFactory<HttpMessageConverters> messageConverters() {
        return () -> new HttpMessageConverters(mappingJackson2HttpMessageConverter());
    }

    public MappingJackson2HttpMessageConverter mappingJackson2HttpMessageConverter() {
        return new MappingJackson2HttpMessageConverter(objectMapper());
    }

    public ObjectMapper objectMapper() {
        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.registerModule(new Jdk8Module());
        objectMapper.setDateFormat(new SimpleDateFormat(DEFAULT_DATE_TIME_FORMAT));
        objectMapper.setTimeZone(TimeZone.getTimeZone("GMT+8"));
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        objectMapper.disable(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS);
        objectMapper.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE);
        JavaTimeModule javaTimeModule = new JavaTimeModule();
        javaTimeModule.addSerializer(LocalDateTime.class, new LocalDateTimeSerializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
        javaTimeModule.addDeserializer(LocalDateTime.class, new LocalDateTimeDeserializer(DateTimeFormatter.ofPattern(DEFAULT_DATE_TIME_FORMAT)));
        objectMapper.registerModule(javaTimeModule).registerModule(new ParameterNamesModule());
        return objectMapper;
    }

Summarize

The exception information is very important, the source code is very important, and the official website is equally important