jackson - Feign 和 HAL/资源

Question

我有一个通过 spring-data-rest 公开资源的服务器，据我所知，它使用了 HAL 或 HATEOAS。但是当我尝试将它与 Feign 结合使用时，我似乎无法注册一个被拾取的 Jackson2HalModule。

我需要做些什么才能将 Feign“客户端”连接到新转换器？它是否使用了另一个 ObjectMapper 而不是我在这里得到的那个？

代码:

@Inject
public void configureObjectMapper(ObjectMapper mapper, RestTemplate template) {
    mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    mapper.registerModule(new Jackson2HalModule());

    MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
    converter.setSupportedMediaTypes(MediaType.parseMediaTypes("application/hal+json"));
    converter.setObjectMapper(mapper);

    template.getMessageConverters().add(converter);
}

来自服务器的响应:

{
  "_links" : {
    "self" : {
      "href" : "http://localhost:13372/user{?page,size,sort}",
      "templated" : true
    },
    "search" : {
      "href" : "http://localhost:13372/user/search"
    }
  },
  "_embedded" : {
    "user" : [ {
      "id" : "5567613e5da543dba4201950",
      "version" : 0,
      "created" : "2015-05-28T18:41:02.685Z",
      "createdBy" : "system test",
      "edited" : "2015-05-28T18:41:02.713Z",
      "editedBy" : "system test",
      "username" : "devuser",
      "email" : "dev@test.com",
      "roles" : [ "USER" ],
      "_links" : {
        "self" : {
          "href" : "http://localhost:13372/user/5567613e5da543dba4201950"
        }
      }
    } ]
  },
  "page" : {
    "size" : 20,
    "totalElements" : 1,
    "totalPages" : 1,
    "number" : 0
  }
}

异常(exception):

Caused by: com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of START_OBJECT token
 at [Source: java.io.PushbackInputStream@7b6c6e70; line: 1, column: 1]
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:762)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:758)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.handleNonArray(CollectionDeserializer.java:275)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:216)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:206)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:25)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3066)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2221)
    at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:205)

Answer 1

我发现了问题。
由于来自 REST API 的响应是单个响应，因此发生异常。所以它未能将其视为实体列表。

当我添加时(基于上面的代码):

mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

有用

编辑:
附带说明一下，我已经像这样实现了 FeignClient:

@Service
@FeignClient(UsersConstants.USER_SERVICE_NAME)
public interface UsersServices {

    @RequestMapping(method = RequestMethod.GET, value = "/user")
    List<User> getUsers();
}

但它应该如何，因为它是一个可分页的资源:

@Service
@FeignClient(UsersConstants.USER_SERVICE_NAME)
public interface UsersServices {

    @RequestMapping(method = RequestMethod.GET, value = "/user")
    List<PagedResources<User>> getUsers();
}

PagedResource 位于 HATEOAS 依赖项中:

<dependency>
    <groupId>org.springframework.hateoas</groupId>
    <artifactId>spring-hateoas</artifactId>
</dependency>

它还有很多其他类可以提供帮助，例如 Resource、Resources 等。