前言

最近项目组用feign调用远程服务，消费端报了如下一个异常

从异常信息可以得出localdatime反序列化出了异常，而这个异常又是因为jackson无法处理导致。因此我们可以为jackson的ObjectMapper适配一下

解决方法

1、在pom.xml引入

    <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>

注： jackson-datatype-jsr310这是用来支持jsr310规范的时间，jackson-datatype-jdk8用来支持新的特定于JDK8的类型，例如Optional

2、替换默认的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;
    }

疑问点：为什么替换了默认的ObjectMapper后，feign就可以处理LocalDateTime

答案就在

@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)));
	}
}

而messageConverters默认的转换器是根据HttpMessageConvertersAutoConfiguration而来

@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具有延迟加载的功能，会根据实际情况加载。springboot的web模块默认会引入Jackson相关包。官网上有这么一段话

这个就说明默认的HttpMessageConverter为MappingJackson2HttpMessageConverter，而MappingJackson2HttpMessageConverter会利用objectMapper来进行序列化和反序列化

上面的的话用代码整理如下

 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;
    }

总结

异常信息很重要，源码很重要，官网同样重要