关于feign:feign请求返回值反序列LocalDateTime异常记录

前言

最近项目组用 feign 调用近程服务，生产端报了如下一个异样

从异样信息能够得出 localdatime 反序列化出了异样，而这个异样又是因为 jackson 无奈解决导致。因而咱们能够为 jackson 的 ObjectMapper 适配一下

解决办法

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 这是用来反对 jsr310 标准的工夫，jackson-datatype-jdk8 用来反对新的特定于 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;
    }

疑难点：为什么替换了默认的 ObjectMapper 后，feign 就能够解决 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 默认的转换器是依据 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 具备提早加载的性能，会依据理论状况加载。springboot 的 web 模块默认会引入 Jackson 相干包。官网上有这么一段话

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

下面的的话用代码整顿如下

 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

异样信息很重要，源码很重要，官网同样重要