聊聊feign的HystrixInvocationHandler

序

本文主要研究一下 feign 的 HystrixInvocationHandler

HystrixInvocationHandler

feign-hystrix-10.2.3-sources.jar!/feign/hystrix/HystrixInvocationHandler.java

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();
  }
}

• HystrixInvocationHandler 实现了 InvocationHandler 接口，其构造器接收 target、dispatch、setterFactory、fallbackFactory；invoke 方法主要是创建 hystrixCommand，然后执行 hystrixCommand 的 execute 或 toObservable 等方法；hystrixCommand 的 run 方法执行 HystrixInvocationHandler.this.dispatch.get(method).invoke(args)，其 getFallback 方法主要是执行 fallbackMethodMap.get(method).invoke(fallback, args)

InvocationHandlerFactory

feign-core-10.2.3-sources.jar!/feign/InvocationHandlerFactory.java

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);
    }
  }
}

• InvocationHandlerFactory 接口定义了 create 方法用于创建 InvocationHandler；它有一个 Default 的实现，其 create 方法创建的是 ReflectiveFeign.FeignInvocationHandler

HystrixFeign

feign-hystrix-10.2.3-sources.jar!/feign/hystrix/HystrixFeign.java

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();}

    //......

  }  

    //......
}

• HystrixFeign.Builder 的 build 方法使用的 InvocationHandlerFactory 创建的是 HystrixInvocationHandler

FeignClientsConfiguration

spring-cloud-openfeign-core-2.2.0.M1-sources.jar!/org/springframework/cloud/openfeign/FeignClientsConfiguration.java

@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();
        }

    }

    //......
}

• FeignClientsConfiguration 的 HystrixFeignConfiguration 在有 HystrixCommand.class, HystrixFeign.class 以及 feign.hystrix.enabled 为 true 的情况下，其创建的 Feign.Builder 为 HystrixFeign.builder

小结

HystrixInvocationHandler 实现了 InvocationHandler 接口，其构造器接收 target、dispatch、setterFactory、fallbackFactory；invoke 方法主要是创建 hystrixCommand，然后执行 hystrixCommand 的 execute 或 toObservable 等方法；hystrixCommand 的 run 方法执行 HystrixInvocationHandler.this.dispatch.get(method).invoke(args)，其 getFallback 方法主要是执行 fallbackMethodMap.get(method).invoke(fallback, args)

doc

• HystrixInvocationHandler