Spring Data REST：单个资源的投影表示

Question

我有一个简单的UserRepository，它使用Spring Data REST公开。下面是user实体类：

@Document(collection = User.COLLECTION_NAME)
@Setter
@Getter
public class User extends Entity {

    public static final String COLLECTION_NAME = "users";

    private String name;
    private String email;
    private String password;
    private Set<UserRole> roles = new HashSet<>(0);
}

我创建了一个UserProjection类，它的外观如下：

@JsonInclude(JsonInclude.Include.NON_NULL)
@Projection(types = User.class)
public interface UserProjection {

    String getId();

    String getName();

    String getEmail();

    Set<UserRole> getRoles();
}

下面是repository类：

@RepositoryRestResource(collectionResourceRel = User.COLLECTION_NAME, path = RestPath.Users.ROOT,
        excerptProjection = UserProjection.class)
public interface RestUserRepository extends MongoRepository<User, String> {

    // Not exported operations

    @RestResource(exported = false)
    @Override
    <S extends User> S insert(S entity);

    @RestResource(exported = false)
    @Override
    <S extends User> S save(S entity);

    @RestResource(exported = false)
    @Override
    <S extends User> List<S> save(Iterable<S> entites);
}

我还在配置中指定了用户投影，以确保它将被使用。

config.getProjectionConfiguration().addProjection(UserProjection.class, User.class);

因此，当我进入/users路径时，我得到以下响应（应用了投影）：

{
  "_embedded" : {
    "users" : [ {
      "name" : "Yuriy Yunikov",
      "id" : "5812193156aee116256a33d4",
      "roles" : [ "USER", "ADMIN" ],
      "email" : "[e-mail]",
      "points" : 0,
      "_links" : {
        "self" : {
          "href" : "http://127.0.0.1:8080/users/5812193156aee116256a33d4"
        },
        "user" : {
          "href" : "http://127.0.0.1:8080/users/5812193156aee116256a33d4{?projection}",
          "templated" : true
        }
      }
    } ]
  },
  "_links" : {
    "self" : {
      "href" : "http://127.0.0.1:8080/users"
    },
    "profile" : {
      "href" : "http://127.0.0.1:8080/profile/users"
    }
  },
  "page" : {
    "size" : 20,
    "totalElements" : 1,
    "totalPages" : 1,
    "number" : 0
  }
}

{
  "name" : "Yuriy Yunikov",
  "email" : "[e-mail]",
  "password" : "123456",
  "roles" : [ "USER", "ADMIN" ],
  "_links" : {
    "self" : {
      "href" : "http://127.0.0.1:8080/users/5812193156aee116256a33d4"
    },
    "user" : {
      "href" : "http://127.0.0.1:8080/users/5812193156aee116256a33d4{?projection}",
      "templated" : true
    }
  }
}

Answer 1

我能够创建一个ResourceProcessor类，它按照DataRest-428中的建议对任何资源应用投影。它的工作方式如下：如果在URL中指定了projection参数--将应用指定的投影，如果不--将返回名称为default的projection，将应用appliced first found投影。另外，我必须添加自定义的projectingresource，它忽略链接，否则返回的JSON中有两个_links键。

/**
 * Projecting resource used for {@link ProjectingProcessor}. Does not include empty links in JSON, otherwise two 
 * _links keys are present in returning JSON.
 *
 * @param <T>
 */
@JsonInclude(JsonInclude.Include.NON_EMPTY)
class ProjectingResource<T> extends Resource<T> {

    ProjectingResource(final T content) {
        super(content);
    }
}

/**
 * Resource processor for all resources which applies projection for single resource. By default, projections
 * are not
 * applied when working with single resource, e.g. http://127.0.0.1:8080/users/580793f642d54436e921f6ca. See
 * related issue <a href="https://jira.spring.io/browse/DATAREST-428">DATAREST-428</a>
 */
@Component
public class ProjectingProcessor implements ResourceProcessor<Resource<Object>> {

    private static final String PROJECTION_PARAMETER = "projection";

    private final ProjectionFactory projectionFactory;

    private final RepositoryRestConfiguration repositoryRestConfiguration;

    private final HttpServletRequest request;

    public ProjectingProcessor(@Autowired final RepositoryRestConfiguration repositoryRestConfiguration,
                               @Autowired final ProjectionFactory projectionFactory,
                               @Autowired final HttpServletRequest request) {
        this.repositoryRestConfiguration = repositoryRestConfiguration;
        this.projectionFactory = projectionFactory;
        this.request = request;
    }

    @Override
    public Resource<Object> process(final Resource<Object> resource) {
        if (AopUtils.isAopProxy(resource.getContent())) {
            return resource;
        }

        final Optional<Class<?>> projectionType = findProjectionType(resource.getContent());
        if (projectionType.isPresent()) {
            final Object projection = projectionFactory.createProjection(projectionType.get(), resource
                    .getContent());
            return new ProjectingResource<>(projection);
        }

        return resource;
    }

    private Optional<Class<?>> findProjectionType(final Object content) {
        final String projectionParameter = request.getParameter(PROJECTION_PARAMETER);
        final Map<String, Class<?>> projectionsForType = repositoryRestConfiguration.getProjectionConfiguration()
                .getProjectionsFor(content.getClass());

        if (!projectionsForType.isEmpty()) {
            if (!StringUtils.isEmpty(projectionParameter)) {
                // projection parameter specified
                final Class<?> projectionClass = projectionsForType.get(projectionParameter);
                if (projectionClass != null) {
                    return Optional.of(projectionClass);
                }
            } else if (projectionsForType.containsKey(ProjectionName.DEFAULT)) {
                // default projection exists
                return Optional.of(projectionsForType.get(ProjectionName.DEFAULT));
            }

            // no projection parameter specified
            return Optional.of(projectionsForType.values().iterator().next());
        }

        return Optional.empty();
    }
}