Spring Data REST

Tips

• Spring HATEOAS 文档
• 单个 Item 会使用 E-Tag 做缓存

@Component
public class SpringDataRestCustomization extends RepositoryRestConfigurerAdapter {

  @Override
  public void configureRepositoryRestConfiguration(RepositoryRestConfiguration config) {

    config.withEntityLookup().
      // 修改 URL 路径上的 ID 属性
      forRepository(UserRepository.class, User::getUsername, UserRepository::findByUsername);
  }
}

NOTES

• ExcerptProjection
  • 片段映射
  • 只针对集合有效
  • 添加额外字段
• RepositoryRestConfigurer
  • Spring Data WebMVC 的配置接口
• RepositoryEntityController
  • WebMVC 入口
• RestMediaTypes
  • application/hal+json
  • application/x-spring-data-compact+json
  • text/uri-list
  • application/json-patch+json
  • application/merge-patch+json
  • application/alps+json
  • application/schema+json
  • application/x-spring-data-verbose+json
• BackendIdConverter
  • 配置 URL 上 id 生成方式
  • @BackendId 可用于注解该配置
• ResourceAssembler
  • 用于构建资源
  • PersistentEntityResourceAssembler : ResourceAssembler<Object, PersistentEntityResource>
    • 将任意对象转换为 PersistentEntityResource
• PersistentEntityJackson2Module
  • PersistentEntityResource 序列化模块
  • AssociationOmittingSerializerModifier
    • 将关联字段移除
    • 不能改动态修改, 因为序列化器构建成功后会缓存

HATEOAS

• Resources
  • 表示一组资源内容
• ResourceProcessor<T extends ResourceSupport>
  • 资源预处理接口
  • ResourceProcessorInvoker
    • 统一调用方法

如何实现动态映射 ?

• 例如通过参数 select=id,name,parent(id,name) 来确定
• PersistentEntityResourceAssemblerArgumentResolver 实现了 PersistentEntityResourceAssembler 的注入
• 注入的 PersistentEntityProjector 是根据参数中的 projection 来创建的
• 通过 ProjectionDefinitions 拿到映射类
• 通过 ProjectionFactory 创建映射, 映射的最终结果就是映射后的内容
• 映射后的内容被封装为 PersistentEntityResource
  • 包含 Link ,Embededs, Content, Entity
• Spel 的映射是通过方法拦截实现的
• TODO

使用虚拟映射字段

@Projection(name = "virtual", types = { Person.class })
public interface VirtualProjection {
  @Value("#{target.firstName} #{target.lastName}")
  String getFullName();
}

覆盖处理方法

@RepositoryRestController
public class ScannerController {

    private final ScannerRepository repository;

    @Autowired
    public ScannerController(ScannerRepository repo) {
        repository = repo;
    }

    @RequestMapping(method = GET, value = "/scanners/search/listProducers")
    public @ResponseBody ResponseEntity<?> getProducers() {
        List<String> producers = repository.listProducers();

        //
        // do some intermediate processing, logging, etc. with the producers
        //

        Resources<String> resources = new Resources<String>(producers);

        resources.add(linkTo(methodOn(ScannerController.class).getProducers()).withSelfRel());

        // add other links as needed

        return ResponseEntity.ok(resources);
    }

}

自定义实体处理

@Bean
public ResourceProcessor<Resource<Person>> personProcessor() {

   return new ResourceProcessor<Resource<Person>>() {

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

      resource.add(new Link("http://localhost:8080/people", "added-link"));
      return resource;
     }
   };
}

添加 Spring Data REST 到现有 Spring MVC 项目

import org.springframework.context.annotation.Import;
import org.springframework.data.rest.webmvc.RepositoryRestMvcConfiguration;

@Configuration
@Import(RepositoryRestMvcConfiguration.class)
public class MyApplicationConfiguration {
  …
}

自定义资源类型处理

@Controller
@ExposesResourceFor(Order.class)
@RequestMapping("/orders")
class OrderController {

  @RequestMapping
  ResponseEntity orders(…) { … }

  @RequestMapping("/{id}")
  ResponseEntity order(@PathVariable("id") … ) { … }
}