想知道如何将@VersionSpring Data REST中的注释用于ETag，但由于某种原因我看不到ETag的填充

@Entity
@EntityListeners(AuditingEntityListener.class)
public class Venue implements Serializable {

  private static final long serialVersionUID = -5516160437873476233L;

  private Long id;

  ...
  // other properties

  private Long version;

  private Date lastModifiedDate;

  // getters & setters

  @JsonIgnore
  @LastModifiedDate
  public Date getLastModifiedDate() {
    return lastModifiedDate;
  }

  @Version
  @Column
  public Long getVersion() {
    return version;
  }

通过文档，这应该给我一个Etag值吗？如该库的摘要所示

protected HttpHeaders prepareHeaders(PersistentEntity<?, ?> entity, Object value) {

    // Add ETag
    HttpHeaders headers = ETag.from(entity, value).addTo(new HttpHeaders());

    // Add Last-Modified
    AuditableBeanWrapper wrapper = getAuditableBeanWrapper(value);

但是，给定实体和以下配置，我仍然获得Version的null。我的应用程序具有以下内容

@SpringBootApplication
@EnableEntityLinks
@EnableJpaAuditing
public class GabbarSinghApplication

其余存储库如下

@RepositoryRestResource(collectionResourceRel = "venue", path = "venues")
public interface VenueRepository extends JpaRepository<Venue, Long> {

虽然我还没有使用标头等测试这些方法，但是由于从版本属性值获取ETag标头值时出现空指针异常，因此一个简单的POST请求http://localhost:8080/workshops给出了一个500原因。

更新资料

移到实体的@ javax.persistence.Version，我仍然没有在响应头中得到ETag头。

这是一个失败的单元测试

  @Before
  public void setUp() throws Exception {

    XStream xstream = new XStream();
    ObjectInputStream in = xstream.createObjectInputStream(venuesXml.getInputStream());
    leela = (Venue) in.readObject();
    paul = (Venue) in.readObject();
    taj = (Venue) in.readObject();
    LOGGER.debug("Initialised Venues from xml file {}", venuesXml.getFilename());

  }

  @Test
  public void testEtagHeaderIsAutoGeneratedOnResourceCreation() {

    final HttpEntity<Venue> httpEntity = new HttpEntity<Venue>(taj, headers);

    ResponseEntity<ResourceSupport> response = restTemplate.exchange(BASE_LOCATION
        + VENUES_ENDPOINT, HttpMethod.POST, httpEntity,
        new ParameterizedTypeReference<ResourceSupport>() {
        });

    assertTrue("Response should contain ETag header", null != response.getHeaders().getETag());

该断言失败。