Jackson 和 Feign 无法反序列化 Spring 的 org.springframework.data.domain.Sort答案

【问题标题】：Jackson with Feign can't deserialized Spring's org.springframework.data.domain.SortJackson 和 Feign 无法反序列化 Spring 的 org.springframework.data.domain.Sort
【发布时间】：2021-01-03 13:40:09
【问题描述】：

问题：一个假装客户端，对返回 Page<T> 的 Spring Boot Rest API 进行 API 调用，无法反序列化该页面的 sort 属性。

Spring Boot：2.3.3.Release
Spring Cloud Feign：2.2.5.RELEASE

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: 不能构造org.springframework.data.domain.Sort 的实例（没有创建者，如默认构造函数，存在）：无法反序列化 [来源：（缓冲读取器）；行：1，列：238]（通过参考链： org.springframework.cloud.openfeign.support.PageJacksonModule$SimplePageImpl["sort"])

不知道为什么注册的PageJacksonModule 似乎不支持这一点。

给定一个手动配置的 Feign 客户端：

public class TelematicsConfig {

  private String host;

  ObjectMapper provideObjectMapper() {
    return new ObjectMapper()
        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
        .setPropertyNamingStrategy(SnakeCaseStrategy.SNAKE_CASE)
        .registerModule(new PageJacksonModule());
  }

  @Bean
  TelematicsClient provideTelematicsClient() {
    return Feign.builder()
        .client(new OkHttpClient())
        .encoder(new JacksonEncoder(provideObjectMapper()))
        .decoder(new JacksonDecoder(provideObjectMapper()))
        .logger(new Slf4jLogger(TelematicsClient.class))
        .logLevel(Logger.Level.FULL)
        .target(TelematicsClient.class, host);
  }

}

客户本身：

public interface TelematicsClient {

  @RequestLine("GET /api/v1/telematics/devices")
  Page<TelematicsDevice> getDevices();

}

当调用它时，我得到：

2020-09-16 12:38:49.707 ERROR 96244 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is feign.FeignException: Cannot construct instance of `org.springframework.data.domain.Sort` (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (BufferedReader); line: 1, column: 238] (through reference chain: org.springframework.cloud.openfeign.support.PageJacksonModule$SimplePageImpl["sort"]) reading GET http://localhost:8081/api/v1/telematics/devices] with root cause

com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.springframework.data.domain.Sort` (no Creators, like default constructor, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
 at [Source: (BufferedReader); line: 1, column: 238] (through reference chain: org.springframework.cloud.openfeign.support.PageJacksonModule$SimplePageImpl["sort"])
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1611)
    at com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:400)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1077)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1320)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:331)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:164)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:542)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:535)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:419)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1310)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:331)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:164)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4482)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3463)
    at feign.jackson.JacksonDecoder.decode(JacksonDecoder.java:61)

任何关于为什么这不起作用的见解将不胜感激。

编辑：以下类似乎暗示支持排序，不是吗？

https://github.com/spring-cloud/spring-cloud-openfeign/blob/master/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/support/PageJacksonModule.java#L69

【问题讨论】：

标签： java spring-boot spring-cloud-feign feign openfeign

【解决方案1】：

如果您使用自动配置的 Feign 客户端，您可以通过打开相应的配置属性来关注Spring Cloud OpenFeign docs：

您可以考虑启用 Jackson Modules 以获得支持 org.springframework.data.domain.Page 和 org.springframework.data.domain.Sort解码。
feign.autoconfiguration.jackson.enabled=true

【讨论】：

哦，太好了！我在文档中错过了这个。这似乎应该是默认设置，如果还没有的话。

【解决方案2】：

找到答案了。

https://github.com/spring-cloud/spring-cloud-openfeign/blob/master/spring-cloud-openfeign-core/src/main/java/org/springframework/cloud/openfeign/support/SortJacksonModule.java

    return new ObjectMapper()
        .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
        .setPropertyNamingStrategy(SnakeCaseStrategy.SNAKE_CASE)
        .registerModule(new PageJacksonModule())
        .registerModule(new SortJacksonModule()); // <-- This.  duh.

【讨论】：