Spring boot data rest，Jackson：Jackson 序列化期间如何使用 URI 而不是相关实体的 id答案

【问题标题】：Spring boot data rest, Jackson: How to use URI instead of id for related entity during Jackson serializationSpring boot data rest，Jackson：Jackson 序列化期间如何使用 URI 而不是相关实体的 id
【发布时间】：2017-05-29 07:48:26
【问题描述】：

我有一对多的关系 b/w Hotel 和 Room 实体。数据流如下：

客户端代码创建没有任何房间的酒店对象
客户端执行 HTTP POST（创建和保留酒店实体）
客户端创建 Room 对象，将其添加到 Hotel
客户端执行 HTTP POST（创建 ROOM 并更新酒店对象）

我在下面的 junit 测试中模拟了上述流程，并遇到了如下所示的异常。

Method: POST
URI: http://localhost:49515/api/hotels
Request Body: {"id":100,"name":"hotel1"

Method: POST
URI: http://localhost:49515/api/rooms
Request Body: {"id":200,"name":"room1","hotel":100}

o.s.d.r.w.RepositoryRestExceptionHandler : Could not read document: Failed to convert from type [java.net.URI] to type [com.example.entities.Hotel] for value '100'; nested exception is java.lang.IllegalArgumentException: Cannot resolve URI 100. Is it local or remote? Only local URIs are resolvable. (through reference chain: com.example.entities.Room["hotel"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException:

问题似乎是在发布 Room 对象创建时，对 Hotel 的引用作为纯 ID 字段发送（在序列化期间），而 Jackson 在反序列化期间无法解析该引用。如何发送酒店的 URI 而不是其 ID？

{"id":200,"name":"room1", "hotel": "http://localhost:49515/api/hotels/100"}

而不是

    {"id":200,"name":"room1", "hotel":100}

是否有其他方法可以解决我的数据流问题？

示例代码如下：

    @Entity
    @Table
    @JsonIdentityInfo(generator=ObjectIdGenerators.PropertyGenerator.class, property="id")
    public class Hotel implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy= GenerationType.AUTO)
        private Integer id;
        private String name;

        @OneToMany(mappedBy="hotel")
        @JsonIgnore
        private Set<Room> rooms;

        public Hotel() {
        }
    // --- getters and setters omitted for brevity ---
    }

    @Entity
    @Table
    @JsonIdentityInfo(generator=ObjectIdGenerators.PropertyGenerator.class, property="id")
    public class Room implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy= GenerationType.AUTO)
        private Integer id;


        @ManyToOne(fetch= FetchType.LAZY)
        @JsonIdentityReference(alwaysAsId=true)
        private Hotel hotel;

        public Room() {
        }
    // --- getters and setters omitted for brevity ---
    }

    public interface HotelRepo extends JpaRepository<Hotel, Integer> {
    }
    public interface RoomRepo extends JpaRepository<Room, Integer> {
    }


    @RunWith(SpringRunner.class)
    @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
    @AutoConfigureTestDatabase(connection = EmbeddedDatabaseConnection.H2)
    public class JPACreationTester {

        static final String CREATE_HOTEL_URL = "/api/hotels";
        static final String CREATE_ROOM_URL = "/api/rooms";

        @Autowired
        private TestRestTemplate restTemplate;

        @Test
        public void testDataCreation () throws Exception {

            String resName1 = "hotel1";
            Hotel hotel1 = new Hotel(resName1);
            hotel1.setId(100);

            String roomName1 = "room1";
            Room room1 = new Room(roomName1);
            room1.setId(200);
            room1.setHotel(hotel1);

            Set<Room> rooms = new HashSet<>();
            rooms.add(room1);
            hotel1.setRooms(rooms);

            Hotel hotel1saved = this.restTemplate.postForObject(CREATE_HOTEL_URL, hotel1, Hotel.class);
            Room room1saved = this.restTemplate.postForObject(CREATE_ROOM_URL, room1, Room.class);
            assertThat(room1saved).as("Rooms are equal").isEqualToIgnoringNullFields(room1);
            assertThat(hotel1saved).as("Hotels are equal").isEqualToIgnoringNullFields(hotel1);
        }
    }

下面的服务器日志

2017-01-13 11:51:47.969 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : Created POST request for "http://localhost:49515/api/hotels"
   2017-01-13 11:51:48.073 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : Setting request Accept header to [application/json, application/json, application/*+json, application/*+json]
   2017-01-13 11:51:48.090 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : Writing [com.example.entities.Hotel@1d9bd1d6] using [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter@10bdfbcc]
   Method: POST
   URI: http://localhost:49515/api/hotels
   Request Body: {"id":100,"name":"hotel1"}
   Response body: java.io.ByteArrayInputStream@23708f14
   2017-01-13 11:51:48.653 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : POST request for "http://localhost:49515/api/hotels" resulted in 201 (null)
   2017-01-13 11:51:48.655 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : Reading [class com.example.entities.Hotel] as "application/json;charset=UTF-8" using [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter@10bdfbcc]
   2017-01-13 11:51:48.656 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : Created POST request for "http://localhost:49515/api/rooms"
   2017-01-13 11:51:48.659 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : Setting request Accept header to [application/json, application/json, application/*+json, application/*+json]
   2017-01-13 11:51:48.660 DEBUG 1217 --- [           main] o.s.web.client.RestTemplate              : Writing [com.example.entities.Room@151659dd] using [org.springframework.http.converter.json.MappingJackson2HttpMessageConverter@10bdfbcc]
   Method: POST
   URI: http://localhost:49515/api/rooms
   Request Body: {"id":200,"hotel":100,"name":"room1"}
   2017-01-13 11:51:48.697 ERROR 1217 --- [o-auto-1-exec-2] o.s.d.r.w.RepositoryRestExceptionHandler : Could not read document: Failed to convert from type [java.net.URI] to type [com.example.entities.Hotel] for value '100'; nested exception is java.lang.IllegalArgumentException: Cannot resolve URI 100. Is it local or remote? Only local URIs are resolvable. (through reference chain: com.example.entities.Room["hotel"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Failed to convert from type [java.net.URI] to type [com.example.entities.Hotel] for value '100'; nested exception is java.lang.IllegalArgumentException: Cannot resolve URI 100. Is it local or remote? Only local URIs are resolvable. (through reference chain: com.example.entities.Room["hotel"])

   org.springframework.http.converter.HttpMessageNotReadableException: Could not read document: Failed to convert from type [java.net.URI] to type [com.example.entities.Hotel] for value '100'; nested exception is java.lang.IllegalArgumentException: Cannot resolve URI 100. Is it local or remote? Only local URIs are resolvable. (through reference chain: com.example.entities.Room["hotel"]); nested exception is com.fasterxml.jackson.databind.JsonMappingException: Failed to convert from type [java.net.URI] to type [com.example.entities.Hotel] for value '100'; nested exception is java.lang.IllegalArgumentException: Cannot resolve URI 100. Is it local or remote? Only local URIs are resolvable. (through reference chain: com.example.entities.Room["hotel"])
     at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:240) ~[spring-web-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readInternal(AbstractJackson2HttpMessageConverter.java:217) ~[spring-web-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.http.converter.AbstractHttpMessageConverter.read(AbstractHttpMessageConverter.java:193) ~[spring-web-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.data.rest.webmvc.config.PersistentEntityResourceHandlerMethodArgumentResolver.read(PersistentEntityResourceHandlerMethodArgumentResolver.java:228) ~[spring-data-rest-webmvc-2.5.6.RELEASE.jar:na]
     at org.springframework.data.rest.webmvc.config.PersistentEntityResourceHandlerMethodArgumentResolver.read(PersistentEntityResourceHandlerMethodArgumentResolver.java:185) ~[spring-data-rest-webmvc-2.5.6.RELEASE.jar:na]
     at org.springframework.data.rest.webmvc.config.PersistentEntityResourceHandlerMethodArgumentResolver.resolveArgument(PersistentEntityResourceHandlerMethodArgumentResolver.java:138) ~[spring-data-rest-webmvc-2.5.6.RELEASE.jar:na]
     at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121) ~[spring-web-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:160) ~[spring-web-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:129) ~[spring-web-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:116) ~[spring-webmvc-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.5.RELEASE.jar:4.3.5.RELEASE]
     at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.5.RELEASE.jar:4.3.5.RELEASE]

【问题讨论】：

标签： spring-boot jackson spring-data-jpa spring-data-rest resttemplate

【解决方案1】：

对初始 POST 的响应将包含一个标头“Location”，它将为您提供新创建酒店的 URI：例如

HTTP/1.1 201 Created
Server: Apache-Coyote/1.1
Location: http://localhost:49515/api/hotels/100
Content-Length: 0
Date: Wed, 26 Feb 2014 20:26:55 GMT

然后您应该能够完全按照您的建议使用“位置”标头的值发布到 /rooms 端点：

{
 "id":200,
 "name":"room1", 
 "hotel": "http://localhost:49515/api/hotels/100"
}

【讨论】：