为具有复合 ID 的实体自定义 HATEOAS 链接生成

Question

我在PageAndSortingRepository 上配置了一个RepositoryRestResource，该PageAndSortingRepository 访问一个包含复合ID 的实体：

@Entity
@IdClass(CustomerId.class)
public class Customer {
    @Id BigInteger id;
    @Id int startVersion;
    ...
}

public class CustomerId {
    BigInteger id;
    int startVersion;
    ...
}

@RepositoryRestResource(collectionResourceRel = "customers", path = "customers", itemResourceRel = "customers/{id}_{startVersion}")
public interface CustomerRepository extends PagingAndSortingRepository<Customer, CustomerId> {}

例如，当我在"http://<server>/api/customers/1_1" 访问服务器时，我以 json 形式返回正确的资源，但 _links 部分中 self 的 href 是错误的，对于我查询的任何其他客户也是如此："http://<server>/api/customer/1"

即：

{
  "id" : 1,
  "startVersion" : 1,
  ...
  "firstname" : "BOB",
  "_links" : {
    "self" : {
      "href" : "http://localhost:9081/reps/api/reps/1" <-- This should be /1_1
    }
  }
}

我想这是因为我的复合 ID，但我很高兴如何更改此默认行为。

我查看了 ResourceSupport 和 ResourceProcessor 类，但不确定我需要进行多少更改才能解决此问题。

知道春天的人可以帮帮我吗？

Answer 1

不幸的是，2.1.0.RELEASE 之前的所有 Spring Data JPA/Rest 版本都无法开箱即用地满足您的需求。 源代码隐藏在 Spring Data Commons/JPA 本身中。 Spring Data JPA 仅支持 Id 和 EmbeddedId 作为标识符。

摘录JpaPersistentPropertyImpl：

static {

    // [...]

    annotations = new HashSet<Class<? extends Annotation>>();
    annotations.add(Id.class);
    annotations.add(EmbeddedId.class);

    ID_ANNOTATIONS = annotations;
}

Spring Data Commons 不支持组合属性的概念。它将一个类的每个属性彼此独立地对待。

当然，您可以破解 Spring Data Rest。但这很麻烦，并没有从根本上解决问题，降低了框架的灵活性。

这里是黑客。这应该让您知道如何解决您的问题。

在您的配置中覆盖repositoryExporterHandlerAdapter 并返回CustomPersistentEntityResourceAssemblerArgumentResolver。 此外，覆盖backendIdConverterRegistry 并将CustomBackendIdConverter 添加到已知id converter 的列表中：

import org.springframework.beans.factory.ListableBeanFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.data.rest.core.projection.ProxyProjectionFactory;
import org.springframework.data.rest.webmvc.RepositoryRestHandlerAdapter;
import org.springframework.data.rest.webmvc.config.RepositoryRestMvcConfiguration;
import org.springframework.data.rest.webmvc.spi.BackendIdConverter;
import org.springframework.data.rest.webmvc.support.HttpMethodHandlerMethodArgumentResolver;
import org.springframework.data.web.config.EnableSpringDataWebSupport;
import org.springframework.hateoas.ResourceProcessor;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.plugin.core.OrderAwarePluginRegistry;
import org.springframework.plugin.core.PluginRegistry;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

@Configuration
@Import(RepositoryRestMvcConfiguration.class)
@EnableSpringDataWebSupport
public class RestConfig extends RepositoryRestMvcConfiguration {
    @Autowired(required = false) List<ResourceProcessor<?>> resourceProcessors = Collections.emptyList();
    @Autowired
    ListableBeanFactory beanFactory;

    @Override
    @Bean
    public PluginRegistry<BackendIdConverter, Class<?>> backendIdConverterRegistry() {

        List<BackendIdConverter> converters = new ArrayList<BackendIdConverter>(3);
        converters.add(new CustomBackendIdConverter());
        converters.add(BackendIdConverter.DefaultIdConverter.INSTANCE);

        return OrderAwarePluginRegistry.create(converters);
    }

    @Bean
    public RequestMappingHandlerAdapter repositoryExporterHandlerAdapter() {

        List<HttpMessageConverter<?>> messageConverters = defaultMessageConverters();
        configureHttpMessageConverters(messageConverters);

        RepositoryRestHandlerAdapter handlerAdapter = new RepositoryRestHandlerAdapter(defaultMethodArgumentResolvers(),
                resourceProcessors);
        handlerAdapter.setMessageConverters(messageConverters);

        return handlerAdapter;
    }

    private List<HandlerMethodArgumentResolver> defaultMethodArgumentResolvers()
    {

        CustomPersistentEntityResourceAssemblerArgumentResolver peraResolver = new CustomPersistentEntityResourceAssemblerArgumentResolver(
                repositories(), entityLinks(), config().projectionConfiguration(), new ProxyProjectionFactory(beanFactory));

        return Arrays.asList(pageableResolver(), sortResolver(), serverHttpRequestMethodArgumentResolver(),
                repoRequestArgumentResolver(), persistentEntityArgumentResolver(),
                resourceMetadataHandlerMethodArgumentResolver(), HttpMethodHandlerMethodArgumentResolver.INSTANCE,
                peraResolver, backendIdHandlerMethodArgumentResolver());
    }
}

创建CustomBackendIdConverter。此类负责呈现您的自定义实体 ID：

import org.springframework.data.rest.webmvc.spi.BackendIdConverter;

import java.io.Serializable;

public class CustomBackendIdConverter implements BackendIdConverter {

    @Override
    public Serializable fromRequestId(String id, Class<?> entityType) {
        return id;
    }

    @Override
    public String toRequestId(Serializable id, Class<?> entityType) {
        if(entityType.equals(Customer.class)) {
            Customer c = (Customer) id;
            return c.getId() + "_" +c.getStartVersion();
        }
        return id.toString();

    }

    @Override
    public boolean supports(Class<?> delimiter) {
        return true;
    }
}

CustomPersistentEntityResourceAssemblerArgumentResolver 反过来应该返回一个CustomPersistentEntityResourceAssembler：

import org.springframework.core.MethodParameter;
import org.springframework.data.repository.support.Repositories;
import org.springframework.data.rest.core.projection.ProjectionDefinitions;
import org.springframework.data.rest.core.projection.ProjectionFactory;
import org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler;
import org.springframework.data.rest.webmvc.config.PersistentEntityResourceAssemblerArgumentResolver;
import org.springframework.data.rest.webmvc.support.PersistentEntityProjector;
import org.springframework.hateoas.EntityLinks;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.ModelAndViewContainer;

public class CustomPersistentEntityResourceAssemblerArgumentResolver extends PersistentEntityResourceAssemblerArgumentResolver {
    private final Repositories repositories;
    private final EntityLinks entityLinks;
    private final ProjectionDefinitions projectionDefinitions;
    private final ProjectionFactory projectionFactory;

    public CustomPersistentEntityResourceAssemblerArgumentResolver(Repositories repositories, EntityLinks entityLinks,
                                                             ProjectionDefinitions projectionDefinitions, ProjectionFactory projectionFactory) {

        super(repositories, entityLinks,projectionDefinitions,projectionFactory);

        this.repositories = repositories;
        this.entityLinks = entityLinks;
        this.projectionDefinitions = projectionDefinitions;
        this.projectionFactory = projectionFactory;
    }

    public boolean supportsParameter(MethodParameter parameter) {
        return PersistentEntityResourceAssembler.class.isAssignableFrom(parameter.getParameterType());
    }

    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
                                  NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {

        String projectionParameter = webRequest.getParameter(projectionDefinitions.getParameterName());
        PersistentEntityProjector projector = new PersistentEntityProjector(projectionDefinitions, projectionFactory,
                projectionParameter);

        return new CustomPersistentEntityResourceAssembler(repositories, entityLinks, projector);
    }
}

CustomPersistentEntityResourceAssembler 需要覆盖 getSelfLinkFor。如您所见，entity.getIdProperty() 返回您的Customer 类的id 或startVersion 属性，该属性又用于在BeanWrapper 的帮助下检索实际值。在这里，我们使用instanceof 运算符将整个框架短路。因此，您的 Customer 类应实现 Serializable 以进行进一步处理。

import org.springframework.data.mapping.PersistentEntity;
import org.springframework.data.mapping.model.BeanWrapper;
import org.springframework.data.repository.support.Repositories;
import org.springframework.data.rest.webmvc.PersistentEntityResourceAssembler;
import org.springframework.data.rest.webmvc.support.Projector;
import org.springframework.hateoas.EntityLinks;
import org.springframework.hateoas.Link;
import org.springframework.util.Assert;

public class CustomPersistentEntityResourceAssembler extends PersistentEntityResourceAssembler {

    private final Repositories repositories;
    private final EntityLinks entityLinks;

    public CustomPersistentEntityResourceAssembler(Repositories repositories, EntityLinks entityLinks, Projector projector) {
        super(repositories, entityLinks, projector);

        this.repositories = repositories;
        this.entityLinks = entityLinks;
    }

    public Link getSelfLinkFor(Object instance) {

        Assert.notNull(instance, "Domain object must not be null!");

        Class<? extends Object> instanceType = instance.getClass();
        PersistentEntity<?, ?> entity = repositories.getPersistentEntity(instanceType);

        if (entity == null) {
            throw new IllegalArgumentException(String.format("Cannot create self link for %s! No persistent entity found!",
                    instanceType));
        }

        Object id;

        //this is a hack for demonstration purpose. don't do this at home!
        if(instance instanceof Customer) {
            id = instance;
        } else {
            BeanWrapper<Object> wrapper = BeanWrapper.create(instance, null);
            id = wrapper.getProperty(entity.getIdProperty());
        }

        Link resourceLink = entityLinks.linkToSingleResource(entity.getType(), id);
        return new Link(resourceLink.getHref(), Link.REL_SELF);
    }
}

就是这样！您应该会看到以下 URI：

{
  "_embedded" : {
    "customers" : [ {
      "name" : "test",
      "_links" : {
        "self" : {
          "href" : "http://localhost:8080/demo/customers/1_1"
        }
      }
    } ]
  }
}

恕我直言，如果您正在从事一个绿色项目，我建议您完全放弃 IdClass 并使用基于 Long 类的技术简单 ID。这是使用 Spring Data Rest 2.1.0.RELEASE、Spring data JPA 1.6.0.RELEASE 和 Spring Framework 4.0.3.RELEASE 测试的。

Answer 2

首先，创建一个 SpringUtil 来从 spring 中获取 bean。

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;

@Component
public class SpringUtil implements ApplicationContextAware {
    private static ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        if(SpringUtil.applicationContext == null) {
            SpringUtil.applicationContext = applicationContext;
        }
    }

    public static ApplicationContext getApplicationContext() {
        return applicationContext;
    }

    public static Object getBean(String name){
        return getApplicationContext().getBean(name);
    }

    public static <T> T getBean(Class<T> clazz){
        return getApplicationContext().getBean(clazz);
    }

    public static <T> T getBean(String name,Class<T> clazz){
        return getApplicationContext().getBean(name, clazz);
    }
}

然后，实现 BackendIdConverter。

import com.alibaba.fastjson.JSON;
import com.example.SpringUtil;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.rest.webmvc.spi.BackendIdConverter;
import org.springframework.stereotype.Component;

import javax.persistence.EmbeddedId;
import javax.persistence.Id;
import java.io.Serializable;
import java.io.UnsupportedEncodingException;
import java.lang.reflect.Method;
import java.net.URLDecoder;
import java.net.URLEncoder;

@Component
public class CustomBackendIdConverter implements BackendIdConverter {

    @Override
    public boolean supports(Class<?> delimiter) {
        return true;
    }

    @Override
    public Serializable fromRequestId(String id, Class<?> entityType) {
        if (id == null) {
            return null;
        }

        //first decode url string
        if (!id.contains(" ") && id.toUpperCase().contains("%7B")) {
            try {
                id = URLDecoder.decode(id, "UTF-8");
            } catch (UnsupportedEncodingException e) {
                e.printStackTrace();
            }
        }

        //deserialize json string to ID object
        Object idObject = null;
        for (Method method : entityType.getDeclaredMethods()) {
            if (method.isAnnotationPresent(Id.class) || method.isAnnotationPresent(EmbeddedId.class)) {
                idObject = JSON.parseObject(id, method.getGenericReturnType());
                break;
            }
        }

        //get dao class from spring
        Object daoClass = null;
        try {
            daoClass = SpringUtil.getBean(Class.forName("com.example.db.dao." + entityType.getSimpleName() + "DAO"));
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

        //get the entity with given primary key
        JpaRepository simpleJpaRepository = (JpaRepository) daoClass;
        Object entity = simpleJpaRepository.findOne((Serializable) idObject);
        return (Serializable) entity;

    }

    @Override
    public String toRequestId(Serializable id, Class<?> entityType) {
        if (id == null) {
            return null;
        }

        String jsonString = JSON.toJSONString(id);

        String encodedString = "";
        try {
            encodedString = URLEncoder.encode(jsonString, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return encodedString;
    }
}

之后。你可以为所欲为。

下面有一个示例。

• 如果实体具有单个属性 pk，您可以使用 localhost:8080/demo/1 正常。根据我的代码，假设 pk 有注释“@Id”。
• 如果实体已经组成了pk，假设pk是demoId类型，并且有 注解“@EmbeddedId”，可以使用 localhost:8080/demo/{demoId json} 获取/放置/删除。并且您的自我链接将是相同的。

Answer 3

虽然不可取，但我已通过在我的 JPA 实体上使用 @EmbeddedId 而不是 IdClass 注释来解决此问题。

像这样：

@Entity
public class Customer {
    @EmbeddedId
    private CustomerId id;
    ...
}

public class CustomerId {

    @Column(...)
    BigInteger key;
    @Column(...)
    int startVersion;
    ...
}

我现在在返回的实体上看到正确生成的链接1_1。

如果有人仍然可以指导我找到不需要我更改模型表示的解决方案，我们将不胜感激。幸运的是，我的应用程序开发没有取得太大进展，因此在更改时会引起严重关注，但我想对于其他人来说，执行这样的更改会产生很大的开销：（例如，更改在 JPQL 中引用此模型的所有查询查询）。

Answer 4

我遇到了一个类似的问题，即数据休息的复合键场景不起作用。 @ksokol 详细解释为解决问题提供了必要的输入。主要为 data-rest-webmvc 和 data-jpa 更改了我的 pom

    <dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-rest-webmvc</artifactId>
        <version>2.2.1.RELEASE</version>
    </dependency>

    <dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-jpa</artifactId>
        <version>1.7.1.RELEASE</version>
    </dependency>

它解决了与复合键相关的所有问题，我不需要进行自定义。感谢 ksokol 的详细解释。