Feign与Hystrix结合

HystrixFeign

Hystrix主要任务是熔断限流，Feign和Hystrix来进行整合可以实现高可用的业务场景。

public final class HystrixFeign {

  public static Builder builder() {
    return new Builder();
  }

  public static final class Builder extends Feign.Builder {

    private Contract contract = new Contract.Default();
    // 构建setterFactory
    private SetterFactory setterFactory = new SetterFactory.Default();

    // 构建setterFactory
    public Builder setterFactory(SetterFactory setterFactory) {
      this.setterFactory = setterFactory;
      return this;
    }

    // 配置fallback
    public <T> T target(Target<T> target, T fallback) {
      // 判断fallback是否为空，不为空通过FallbackFactory构建一个fallbackFactory
      return build(fallback != null ? new FallbackFactory.Default<T>(fallback) : null)
          .newInstance(target);
    }

    // 配置fallbackFactory
    public <T> T target(Target<T> target, FallbackFactory<? extends T> fallbackFactory) {
      // 构建创建实例
      return build(fallbackFactory).newInstance(target);
    }

   // 配置Target返回实例对象
    public <T> T target(Class<T> apiType,
                        String url,
                        FallbackFactory<? extends T> fallbackFactory) {
      return target(new Target.HardCodedTarget<T>(apiType, url), fallbackFactory);
    }

    @Override
    public Feign.Builder invocationHandlerFactory(InvocationHandlerFactory invocationHandlerFactory) {
      throw new UnsupportedOperationException();
    }

    @Override
    public Builder contract(Contract contract) {
      this.contract = contract;
      return this;
    }

    @Override
    public Feign build() {
      return build(null);
    }

    /** Configures components needed for hystrix integration. */
    Feign build(final FallbackFactory<?> nullableFallbackFactory) {
      // 设置代理工厂
      super.invocationHandlerFactory(new InvocationHandlerFactory() {
        @Override
        public InvocationHandler create(Target target,
                                        Map<Method, MethodHandler> dispatch) {
          // 使用Hystrix的代理工厂处理器
          return new HystrixInvocationHandler(target, dispatch, setterFactory,
              nullableFallbackFactory);
        }
      });
      // 设置Contract
      super.contract(new HystrixDelegatingContract(contract));
      return super.build();
    }

    //…… 忽略默认的处理方法
  }
}

相对于Feign的默认信息，HystrixFeign通过自己的HystrixInvocationHandler来实现了代理处理。

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());
  }

  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();
    }

    // 构建HystrixCommand
    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) {
              // 如果fallbackFactory为空执行HystrixCommand默认fallback
              return super.getFallback();
            }
            try {
              // 构建fallback
              Object fallback = fallbackFactory.create(getExecutionException());
              // 代理执行fallback
              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());
            }
          }
        };

    // 执行hystrixCommand
    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());
  }

 //……忽略部分方法
}

最终的结果就是通过HystrixCommand来进行包装最终执行execute，调用feign的invoke方法。