聊聊feign的HystrixInvocationHandler

final class HystrixInvocationHandler implements InvocationHandler {
​
  private final Target<?> target;
  private final Map<Method, MethodHandler> dispatch;
  private final FallbackFactory<?> fallbackFactory; // Nullable
  private final Map<Method, Method> fallbackMethodMap;
  private final Map<Method, Setter> setterMethodMap;
​
  HystrixInvocationHandler(Target<?> target, Map<Method, MethodHandler> dispatch,
      SetterFactory setterFactory, FallbackFactory<?> fallbackFactory) {
    this.target = checkNotNull(target, "target");
    this.dispatch = checkNotNull(dispatch, "dispatch");
    this.fallbackFactory = fallbackFactory;
    this.fallbackMethodMap = toFallbackMethod(dispatch);
    this.setterMethodMap = toSetters(setterFactory, target, dispatch.keySet());
  }
​
  /**
   * If the method param of InvocationHandler.invoke is not accessible, i.e in a package-private
   * interface, the fallback call in hystrix command will fail cause of access restrictions. But
   * methods in dispatch are copied methods. So setting access to dispatch method doesn't take
   * effect to the method in InvocationHandler.invoke. Use map to store a copy of method to invoke
   * the fallback to bypass this and reducing the count of reflection calls.
   *
   * @return cached methods map for fallback invoking
   */
  static Map<Method, Method> toFallbackMethod(Map<Method, MethodHandler> dispatch) {
    Map<Method, Method> result = new LinkedHashMap<Method, Method>();
    for (Method method : dispatch.keySet()) {
      method.setAccessible(true);
      result.put(method, method);
    }
    return result;
  }
​
  /**
   * Process all methods in the target so that appropriate setters are created.
   */
  static Map<Method, Setter> toSetters(SetterFactory setterFactory,
                                       Target<?> target,
                                       Set<Method> methods) {
    Map<Method, Setter> result = new LinkedHashMap<Method, Setter>();
    for (Method method : methods) {
      method.setAccessible(true);
      result.put(method, setterFactory.create(target, method));
    }
    return result;
  }
​
  @Override
  public Object invoke(final Object proxy, final Method method, final Object[] args)
      throws Throwable {
    // early exit if the invoked method is from java.lang.Object
    // code is the same as ReflectiveFeign.FeignInvocationHandler
    if ("equals".equals(method.getName())) {
      try {
        Object otherHandler =
            args.length > 0 && args[0] != null ? Proxy.getInvocationHandler(args[0]) : null;
        return equals(otherHandler);
      } catch (IllegalArgumentException e) {
        return false;
      }
    } else if ("hashCode".equals(method.getName())) {
      return hashCode();
    } else if ("toString".equals(method.getName())) {
      return toString();
    }
​
    HystrixCommand<Object> hystrixCommand =
        new HystrixCommand<Object>(setterMethodMap.get(method)) {
          @Override
          protected Object run() throws Exception {
            try {
              return HystrixInvocationHandler.this.dispatch.get(method).invoke(args);
            } catch (Exception e) {
              throw e;
            } catch (Throwable t) {
              throw (Error) t;
            }
          }
​
          @Override
          protected Object getFallback() {
            if (fallbackFactory == null) {
              return super.getFallback();
            }
            try {
              Object fallback = fallbackFactory.create(getExecutionException());
              Object result = fallbackMethodMap.get(method).invoke(fallback, args);
              if (isReturnsHystrixCommand(method)) {
                return ((HystrixCommand) result).execute();
              } else if (isReturnsObservable(method)) {
                // Create a cold Observable
                return ((Observable) result).toBlocking().first();
              } else if (isReturnsSingle(method)) {
                // Create a cold Observable as a Single
                return ((Single) result).toObservable().toBlocking().first();
              } else if (isReturnsCompletable(method)) {
                ((Completable) result).await();
                return null;
              } else if (isReturnsCompletableFuture(method)) {
                return ((Future) result).get();
              } else {
                return result;
              }
            } catch (IllegalAccessException e) {
              // shouldn't happen as method is public due to being an interface
              throw new AssertionError(e);
            } catch (InvocationTargetException | ExecutionException e) {
              // Exceptions on fallback are tossed by Hystrix
              throw new AssertionError(e.getCause());
            } catch (InterruptedException e) {
              // Exceptions on fallback are tossed by Hystrix
              Thread.currentThread().interrupt();
              throw new AssertionError(e.getCause());
            }
          }
        };
​
    if (Util.isDefault(method)) {
      return hystrixCommand.execute();
    } else if (isReturnsHystrixCommand(method)) {
      return hystrixCommand;
    } else if (isReturnsObservable(method)) {
      // Create a cold Observable
      return hystrixCommand.toObservable();
    } else if (isReturnsSingle(method)) {
      // Create a cold Observable as a Single
      return hystrixCommand.toObservable().toSingle();
    } else if (isReturnsCompletable(method)) {
      return hystrixCommand.toObservable().toCompletable();
    } else if (isReturnsCompletableFuture(method)) {
      return new ObservableCompletableFuture<>(hystrixCommand);
    }
    return hystrixCommand.execute();
  }
​
  private boolean isReturnsCompletable(Method method) {
    return Completable.class.isAssignableFrom(method.getReturnType());
  }
​
  private boolean isReturnsHystrixCommand(Method method) {
    return HystrixCommand.class.isAssignableFrom(method.getReturnType());
  }
​
  private boolean isReturnsObservable(Method method) {
    return Observable.class.isAssignableFrom(method.getReturnType());
  }
​
  private boolean isReturnsCompletableFuture(Method method) {
    return CompletableFuture.class.isAssignableFrom(method.getReturnType());
  }
​
  private boolean isReturnsSingle(Method method) {
    return Single.class.isAssignableFrom(method.getReturnType());
  }
​
  @Override
  public boolean equals(Object obj) {
    if (obj instanceof HystrixInvocationHandler) {
      HystrixInvocationHandler other = (HystrixInvocationHandler) obj;
      return target.equals(other.target);
    }
    return false;
  }
​
  @Override
  public int hashCode() {
    return target.hashCode();
  }
​
  @Override
  public String toString() {
    return target.toString();
  }
}

public interface InvocationHandlerFactory {
​
  InvocationHandler create(Target target, Map<Method, MethodHandler> dispatch);
​
  /**
   * Like {@link InvocationHandler#invoke(Object, java.lang.reflect.Method, Object[])}, except for a
   * single method.
   */
  interface MethodHandler {
​
    Object invoke(Object[] argv) throws Throwable;
  }
​
  static final class Default implements InvocationHandlerFactory {
​
    @Override
    public InvocationHandler create(Target target, Map<Method, MethodHandler> dispatch) {
      return new ReflectiveFeign.FeignInvocationHandler(target, dispatch);
    }
  }
}

public final class HystrixFeign {
    //......
​
  public static final class Builder extends Feign.Builder {
​
    private Contract contract = new Contract.Default();
    private SetterFactory setterFactory = new SetterFactory.Default();
​
    //......
​
    @Override
    public Feign build() {
      return build(null);
    }
​
    /** Configures components needed for hystrix integration. */
    Feign build(final FallbackFactory<?> nullableFallbackFactory) {
      super.invocationHandlerFactory(new InvocationHandlerFactory() {
        @Override
        public InvocationHandler create(Target target,
                                        Map<Method, MethodHandler> dispatch) {
          return new HystrixInvocationHandler(target, dispatch, setterFactory,
              nullableFallbackFactory);
        }
      });
      super.contract(new HystrixDelegatingContract(contract));
      return super.build();
    }
​
    //......
​
  }  
​
    //......
}

@Configuration
public class FeignClientsConfiguration {
    
    //......
​
    @Configuration
    @ConditionalOnClass({ HystrixCommand.class, HystrixFeign.class })
    protected static class HystrixFeignConfiguration {
​
        @Bean
        @Scope("prototype")
        @ConditionalOnMissingBean
        @ConditionalOnProperty(name = "feign.hystrix.enabled")
        public Feign.Builder feignHystrixBuilder() {
            return HystrixFeign.builder();
        }
​
    }
​
    //......
}