给定一个 Spring Data Rest URI，你如何找到关联的目标存储库？

Question

I'm building an application using Spring Data REST and implementing an interceptor pattern using a MappedInterceptor as suggested in this post . The interceptor works as expected and it intercepts @RestControllers .

Now, using the parameters available in the preHandle(…) method signature (these include: HttpServletRequest request, HttpServletResponse response, Object handler => can be casted to org.springframework.web.method.HandlerMethod ), how can I access the RestRepository class or repository Method being invoked (the getMethod() , from the HandlerMethod class, works great with Concrete classes, but it does not work with Repository interfaces, it ends returning a RestAbstractController class that invokes the target repository through reflection)???

Why I need this?

Because, I´m doing a cross-cutting logic that needs to access the Repository interface to find a specific business annotation, if the annotation is present, some logic is done (like setting MDC special values, for example)...

Thanks...

Answer 1

The most flexible way to generically lookup and use Spring Data repositories is through the Repositories and RepositoryInvoker abstractions. The former provides by-type lookup abilities of metadata about the repositories and the repositories themselves. The latter allows generic invocation of CRUD and query methods on those repositories. This additional abstraction is necessary as Spring Data repositories don't have to implement a special interface as long as they expose methods that are syntactically equivalent to the ones provided in Spring Data's CrudRepository .

The general way

If you know about the actual domain class you're trying to access the repository for you can get an instance of Repositories injected into your class. That one in turn allows you to lookup entity and repository information as well as the repository itself.

As the latter doesn't have to implement a dedicated interface mandatorily, Repositories.getRepositoryFor(…) only returns Optional<Object> which isn't too helpful if you want to actually do stuff on the repository. RepositoryInvokerFactory allows you to create RepositoryInvoker instances that allow you to invoke certain methods on a repository explicitly independent of way they're actually declared.

@Component
@RequiredArgsConstructor
class SomeComponent {

  private final Repositories repositories;

  public <T> void someMethod(Class<T> type) {

    … = repositories.getEntityInformation(type);

    RepositoryInvokerFactory factory = new DefaultRepositoryInvokerFactory(repositories);
    RepositoryInvoker invoker = factory.getInvokerFor(type);
    Optional<T> entity = invoker.invokeFindById(4711);
  }
}

Note, that a Repositories instance is available as Spring Bean if you use Spring Data REST. If you don't simply declare a bean for it. All it needs is a ListableBeanFactory .

Spring Data REST

With Spring Data REST in the picture on might get into the need to lookup the repository that's backing a particular path segment of the URI. That additional knowledge is encoded in RepositoryResourceMappings which can be used to find out about the domain type that's accessed:

RepositoryResourceMappings mappings = … // get injected

Optional<Class<?>> domainType = mappings.stream()
  .filter(metadata -> metadata.getPath().matches(pathSegment))
  .findFirst()
  .map(ResourceMetadata::getDomainType);

The discovered type can now be used to obtain the repository instance from Repositories . Spring Data REST also provides a preconfigured instance of RepositoryInvokerFactory that applies potentially registered custom EntityLookup instances. Ie using that is preferred to creating an own one like shown above.