伪装和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，它使用的是HAL或HATEOAS。但当我尝试将它与Feign结合使用时，我似乎无法注册被拾取的Jackson2HalModule。

有没有什么我必须做的连接假“客户端”到新的转换器？它是否使用了与我在这里得到的不同的ObjectMapper？

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
  }
}

例外：

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

我找到问题了。发生异常的原因是来自REST API的响应是单个响应。所以它没有把它看作是一个实体列表。

当我添加(基于上面的代码)时：

mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

它起作用了

编辑:顺便说一句，我像这样实现了FeignClient：

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

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

但它应该是什么样子，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();
}

可以在HATEOAS依赖中找到PagedResource：

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

它还有很多其他的类可以提供帮助，比如Resource、Resources等等。

Answer 2

这对我很有效：

@EnableHypermediaSupport(type = EnableHypermediaSupport.HypermediaType.HAL)
@SpringBootApplication
@EnableFeignClients
public class Application {
....
}

请注意@EnableHypermediaSupport

@FeignClient(url = "http://localhost:8080")
public interface PersonClient {
    @RequestMapping(method = RequestMethod.GET, value = "/persons")
    Resources<Person> getPersons();

    @RequestMapping(method = RequestMethod.GET, value = "/persons/{id}")
    Resource<Person> getPerson(@PathVariable("id") long id);
}

我在这里创建了一个完整的工作示例：https://github.com/jtdev/spring-feign-data-rest-example

请注意，简单地将maven pom从spring-boot切换到spring-cloud (不更改代码)很容易导致json错误。

Answer 3

您应该在应用程序中定义一个feignDecoder bean。如果您的环境中有spring-hateoas，请尝试如下所示：

@Bean
public Decoder feignDecoder() {
    ObjectMapper mapper = new ObjectMapper()
            .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
            .registerModule(new Jackson2HalModule());

    return new ResponseEntityDecoder(new JacksonDecoder(mapper));
}

然后，您可以将您的HAL作为PagedResource使用。