java - 如何使 HK2 ServiceLocator 使用桥接自 ServiceLocator 的单例服务实例？

Question

我们正在使用 ExtrasUtilities.bridgeServiceLocator() 通过将应用 ServiceLocator 桥接到 Jersey ServiceLocator，将在一个 ServiceLocator 中创建的现有单例应用程序服务注入(inject) Jersey RESTful Web 服务。

然而，存在于“外部”定位器中的单例并没有被使用——每个服务在注入(inject) Jersey 服务时都会被再次创建。似乎 Singleton 仅在 ServiceLocator 的范围内可见，即使它是桥接的。

这是预期的行为吗？如果是这样，是否有任何方法可以改变这种行为并在桥接的 ServiceLocators 中拥有真正的单例？

我已将问题提取到一组测试类中，这些类说明了以下要点:

public class BridgedServiceTest
{
  private ServiceLocator _outerServiceLocator;
  private ServiceLocator _innerServiceLocator;

  @Test
  public void testBridgedInnerServiceOK() throws Exception
  {
    ServiceLocatorFactory serviceLocatorFactory = ServiceLocatorFactory.getInstance();

    _outerServiceLocator = serviceLocatorFactory.create("Outer");
    ServiceLocatorUtilities.addClasses(_outerServiceLocator, SingletonServiceImpl.class);

    _innerServiceLocator = serviceLocatorFactory.create("Inner");
    ExtrasUtilities.bridgeServiceLocator(_innerServiceLocator, _outerServiceLocator);

    final Client client1 = new Client();
    _outerServiceLocator.inject(client1);
    assertThat(SingletonServiceImpl.instanceCount.get(), Matchers.is(1));
    client1.test();

    final Client client2 = new Client();
    _innerServiceLocator.inject(client2);
    // next line fails as instance count is 2
    assertThat(SingletonServiceImpl.instanceCount.get(), Matchers.is(1));
    client2.test();
  }

  @After
  public void tearDown() throws Exception
  {
    _innerServiceLocator.shutdown();
    _outerServiceLocator.shutdown();
  }
}

@Contract
public interface SingletonService
{
  void fulfil();
}

@Service
public class SingletonServiceImpl implements SingletonService
{
  public static AtomicInteger instanceCount = new AtomicInteger();

  @PostConstruct
  public void postConstruct()
  {
    instanceCount.incrementAndGet();
  }

  @Override
  public void fulfil()
  {
    System.out.println("Contract Fulfilled.");
  }
}

public class Client
{
  @Inject
  private SingletonService _singletonService;

  public void test()
  {
    _singletonService.fulfil();
  }

  public SingletonService getSingletonService()
  {
    return _singletonService;
  }
}

Answer 1

与此同时(如果确实是设计行为)，我通过实现自己的 InjectionResolver 实现了解决方法。它不是一个完整的解决方案，因为它只适用于注入(inject)(即调用 ServiceLocator.getService() 不会桥接)但它可以满足我现在的需要。

如果有人需要的话，这里是类(class)。不是调用 ExtrasUtilities.bridgeServiceLocator(_innerServiceLocator, _outerServiceLocator);，而是调用 BridgingInjectionResolver.bridgeInjection(_innerServiceLocator, _outerServiceLocator);

@Singleton
@Rank(1)
public class BridgingInjectionResolver implements InjectionResolver<Inject>
{
  @Inject
  private ServiceLocator _localServiceLocator;

  private ServiceLocator _remoteServiceLocator;

  public BridgingInjectionResolver()
  {
  }

  /**
   * This method will bridge injection of all non-local services from the from ServiceLocator into the into
   * ServiceLocator.  The two ServiceLocators involved must not have a parent/child relationship
   *
   * @param into The non-null ServiceLocator that will be able to inject services from the from ServiceLocator
   * @param from The non-null ServiceLocator that will provide services for injection to the into ServiceLocator
   */
  public static void bridgeInjection(ServiceLocator into, ServiceLocator from)
  {
    checkParentage(into, from);
    checkParentage(from, into);
    ServiceLocatorUtilities.addClasses(into, BridgingInjectionResolver.class);
    into.getService(BridgingInjectionResolver.class).setRemoteServiceLocator(from);
  }

  private static void checkParentage(ServiceLocator a, ServiceLocator b)
  {
    ServiceLocator originalA = a;

    while (a != null) {
      if (a.getLocatorId() == b.getLocatorId()) {
        throw new IllegalStateException("Locator " + originalA + " is a child of or is the same as locator " + b);
      }

      a = a.getParent();
    }
  }

  @Override
  public Object resolve(Injectee injectee, ServiceHandle<?> root)
  {
    ActiveDescriptor<?> ad = _localServiceLocator.getInjecteeDescriptor(injectee);
    if (ad != null) {
      return _localServiceLocator.getService(ad, root, injectee);
    }
    ad = _remoteServiceLocator.getInjecteeDescriptor(injectee);
    if ((ad != null) && (ad.getDescriptorVisibility() == DescriptorVisibility.LOCAL)) {
      ad = null;
    }
    if (ad == null) {
      if (injectee.isOptional()) {
        return null;
      }

      throw new MultiException(new UnsatisfiedDependencyException(injectee));
    }
    return _remoteServiceLocator.getService(ad, root, injectee);
  }

  @Override
  public boolean isConstructorParameterIndicator()
  {
    return false;
  }

  @Override
  public boolean isMethodParameterIndicator()
  {
    return false;
  }

  private void setRemoteServiceLocator(ServiceLocator remoteServiceLocator)
  {
    _remoteServiceLocator = remoteServiceLocator;
  }

}