如何使 HK2 服务定位器使用桥接的服务定位器中的单例服务实例？

Question

我们使用using ExtrasUtilities.bridgeServiceLocator()通过桥接应用ServiceLocator到Jersey ServiceLocator，将在一个ServiceLocator中创建的现有单例应用服务注入到Jersey rest式Web服务中。

然而，存在于"外部"定位器中的单例没有被使用——当注入到Jersey服务中时，每个服务都被重新创建。似乎Singleton只在ServiceLocator的作用域中可见，即使它是桥接的。

这是预期的行为吗?如果是这样，有没有办法改变这种行为，并在桥接ServiceLocators之间拥有一个真正的单例?

我已经将问题提取到一组测试类中，这些测试类说明了下面的要点:

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

同时(如果它确实是设计行为)，我通过实现我自己的InjectionResolver实现了一个解决方案。这不是一个完整的解决方案，因为它只适用于注入(即调用ServiceLocator.getService()不会桥接)，但它做了我现在需要的。

如果有人需要的话，这是课程。不叫ExtrasUtilities.bridgeServiceLocator(_innerServiceLocator, _outerServiceLocator);，叫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;
  }
}

Answer 2

ServiceLocator桥存在一个bug，目前已经修复。修复将在hk2 2.5.0-b07或更高的版本!