覆盖 Spring Data REST 中的相关链接

Question

我正在使用 Spring Boot 2、Spring Data REST、Spring HATEOAS。

假设我有一个模型：

@EntityListeners({ContactListener.class})
@Data
@EqualsAndHashCode(callSuper = true)
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Contact extends AbstractEntity {

    @NotNull
    @Enumerated(EnumType.STRING)
    @Column(nullable = false, columnDefinition = "VARCHAR(30) DEFAULT 'CUSTOMER'")
    private ContactType type = ContactType.CUSTOMER;

    @NotNull
    @Enumerated(EnumType.STRING)
    @Column(nullable = false, columnDefinition = "VARCHAR(30) DEFAULT 'NATURAL_PERSON'")
    private PersonType personType = PersonType.NATURAL_PERSON;

    private String firstName;

    private String lastName;

    private String companyName;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "store_id", updatable = false)
    private Store store;

和商店：

@Data
@EqualsAndHashCode(callSuper = true)
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Store extends AbstractEntity {

    @NotBlank
    @Column(nullable = false)
    private String name;

    @Username
    @NotBlank
    @Length(max = 16)
    @Column(nullable = false/*, unique = true*/)
    @ColumnTransformer(write = "UPPER(?)")
    private String code;

    private String address;

    private String zipCode;

    private String city;

    private String district;

当我收到联系信息时，回复如下所示：

{
    "sid": "962732c2-68a8-413b-9762-f676d42046b4",
    "createdBy": "1ccf2329-4aa3-4d55-8878-25517edf1522",
    "createdDate": "2019-05-28T14:06:07.011Z",
    "lastModifiedDate": "2019-06-04T08:46:02.591Z",
    "lastModifiedBy": "system",
    "createdByName": "Rossi Mario",
    "lastModifiedByName": null,
    "type": "CUSTOMER",
    "personType": "NATURAL_PERSON",
    "firstName": "Mario",
    "lastName": "Rossi",
    "companyName": null,
    "fullName": "Rossi Mario",
    "gender": "MALE",
    "birthDate": "2019-05-21T00:00:00Z",
    "birthCity": null,
    "job": null,
    "billingAddress": "Via 123",
    "billingZipCode": "14018",
    "billingCity": "Roatto",
    "billingDistrict": "AT",
    "billingCountry": "IT",
    "shippingAddress": "Via 123",
    "shippingZipCode": "14018",
    "shippingCity": "Roatto",
    "shippingDistrict": "AT",
    "shippingCountry": "IT",
    "taxCode": "XXXX",
    "vatNumber": null,
    "landlinePhone": null,
    "mobilePhone": null,
    "fax": null,
    "email": "[email protected]",
    "certifiedEmail": null,
    "survey": null,
    "iban": null,
    "swift": null,
    "publicAdministration": false,
    "sdiAccountId": "0000000",
    "preset": false,
    "_links": {
        "self": {
            "href": "http://localhost:8082/api/v1/contacts/1"
        },
        "contact": {
            "href": "http://localhost:8082/api/v1/contacts/1{?projection}",
            "templated": true
        },
        "store": {
            "href": "http://localhost:8082/api/v1/contacts/1/store{?projection}",
            "templated": true
        }
    }
}

正如您所看到的商店链接，它不是资源商店的self链接。我想覆盖该链接设置自身资源。所以我创建了这个处理器：

@Component
public class DocumentRowProcessor implements ResourceProcessor<Resource<Contact>> {

    @Autowired
    private BasePathAwareLinks service;

    @Autowired
    private EntityLinks entityLinks;

    @Override
    public Resource<Contact> process(Resource<Contact> resource) {

        Store store = resource.getContent().getStore();
        if(store != null){
           resource.add(entityLinks.linkToSingleResource(store.getClass(), store.getId()).withRel("store"));
        }

        return resource;
    }
}

不幸的是，该链接现已被覆盖，但我在“商店”内找到了 2 个链接。调试我看到资源内部仅存在自我链接。我的猜测是在以下步骤中添加了相关链接。

如何干净利落地完成我的目标？

Answer 1

hateoas 链接在序列化期间添加到结果中（使用特定的 JSON 序列化程序），因此您无法使用 ResourceProcessor 删除它。

proper 链接。 http://localhost:8082/api/v1/contacts/1/store

 是端点，您可以在其中检查哪个商店链接到该内容，或者您可以删除/修改这两个对象之间的关联。

但是，在某些用例中，您需要自链接才能执行进一步操作，并且您不希望从客户端发送额外的请求。请执行下列操作： 1. 为内容创建投影。 2. 包括您需要的所有房产以及商店。 3. 如果您不需要此处商店的任何属性（仅需要自链接），则为商店实体创建一个“空投影”，并将该投影作为商店属性包含到联系人属性中。

当您获得联系人的投影时，结果将包含商店

内部商店属性的自链接。因此，主要的 _links

 集合仍然是常规的 hatos 链接集合，但会有一个

store._links.self.href

 属性，其中包含关联商店的自链接。

Answer 2

从 Spring Data REST 3.6.0 开始，您可以实现新的

LinkCollector

。以下内容有明显的缺陷，我无法测试 Java 版本（我的 Kotlin 版本工作正常），但它使用规范 URL 生成链接：

import org.springframework.data.mapping.Association;
import org.springframework.data.mapping.PersistentEntity;
import org.springframework.data.mapping.PersistentProperty;
import org.springframework.data.mapping.context.PersistentEntities;
import org.springframework.data.rest.core.mapping.ResourceMapping;
import org.springframework.data.rest.core.mapping.ResourceMetadata;
import org.springframework.data.rest.core.support.SelfLinkProvider;
import org.springframework.data.rest.webmvc.mapping.Associations;
import org.springframework.data.rest.webmvc.mapping.LinkCollector;
import org.springframework.hateoas.IanaLinkRelations;
import org.springframework.hateoas.Link;
import org.springframework.hateoas.LinkRelation;
import org.springframework.hateoas.Links;

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;

// https://github.com/spring-projects/spring-data-rest/issues/2042#issuecomment-1913914052
public class AbsoluteLinkCollector implements LinkCollector {

    private final PersistentEntities entities;
    private final Associations associationLinks;
    private final SelfLinkProvider links;

    public AbsoluteLinkCollector(LinkCollector oldCollector) throws NoSuchFieldException, IllegalAccessException {
        Field entitiesField = oldCollector.getClass().getDeclaredField("entities");
        entitiesField.setAccessible(true);
        this.entities = (PersistentEntities) entitiesField.get(oldCollector);

        Field associationLinksField = oldCollector.getClass().getDeclaredField("associationLinks");
        associationLinksField.setAccessible(true);
        this.associationLinks = (Associations) associationLinksField.get(oldCollector);

        Field linksField = oldCollector.getClass().getDeclaredField("links");
        linksField.setAccessible(true);
        this.links = (SelfLinkProvider) linksField.get(oldCollector);
    }

    @Override
    public Links getLinksFor(Object obj) {
        return this.getLinksFor(obj, Links.NONE);
    }

    @Override
    public Links getLinksFor(Object obj, Links existing) {
        Map<String, Link> linkMap = new HashMap<>();
        for (Link l : existing) {
            linkMap.put(l.getRel().value(), l);
        }

        linkMap.put(IanaLinkRelations.SELF.value(), links.createSelfLinkFor(obj).withSelfRel());

        PersistentEntity<?, ? extends PersistentProperty<?>> entity = entities.getRequiredPersistentEntity(obj.getClass());
        entity.doWithAssociations((Association<?> assoc) -> {
            try {
                if (!associationLinks.isLinkableAssociation(assoc)) {
                    return;
                }

                ResourceMetadata ownerMetadata = associationLinks.getMetadataFor(assoc.getInverse().getOwner().getType());
                ResourceMapping propertyMapping = ownerMetadata.getMappingFor(assoc.getInverse());
                LinkRelation rel = propertyMapping.getRel();

                // if it is a collection, we can't get the value
                if (assoc.getInverse().isCollectionLike()) {
                    return;
                }

                Field fieldValueField = obj.getClass().getDeclaredField(assoc.getInverse().getName());
                fieldValueField.setAccessible(true);
                Object fieldValue = fieldValueField.get(obj);
                if (fieldValue == null) return;

                linkMap.put(rel.value(), links.createSelfLinkFor(fieldValue).withRel(rel));
            } catch (Exception e) {
                // without this, we get a useless and confusing "Failed to write request"
                // error response.
                System.out.println("Error getting links for " + obj);
                e.printStackTrace();
                throw new RuntimeException(e);
            }
        });

        return Links.of(linkMap.values());
    }

    @Override
    public Links getLinksForNested(Object obj, Links existing) {
        return this.getLinksFor(obj, existing);
    }
}

它可以通过覆盖

customizeLinkCollector

 中的

RepositoryRestConfigurer

 来启用：

@Configuration
public class RestConfiguration extends RepositoryRestConfigurerAdapter {
    @Override
    public LinkCollector customizeLinkCollector(LinkCollector collector) {
        return new AbsoluteLinkCollector(collector);
    }
}

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