Feign整合Ribbon和Hystrix源码解析

在上篇文章Feign自动装配中，我们提到了Feign的自动装配的原理,以及Feign整合Ribbon和Hystrix的核心在类FeignClientFactoryBean中，那么本篇文章就来揭开这个类的神秘面纱

首先，我们看到这个类实现了FactoryBean这个接口，这个接口的主要作用就是利用getObject()来创建一些实例化过程比较复杂的bean，更多关于这个接口的内容可以参考这篇文章：Spring扩展点之FactoryBean接口

我们直接来看这个类的getObject方法：

    public Object getObject() throws Exception {
        FeignContext context = applicationContext.getBean(FeignContext.class);
        Feign.Builder builder = feign(context);

        if (!StringUtils.hasText(this.url)) {
            String url;
            if (!this.name.startsWith("http")) {
                url = "http://" + this.name;
            }
            else {
                url = this.name;
            }
            url += cleanPath();
            return loadBalance(builder, context, new HardCodedTarget<>(this.type,
                    this.name, url));
        }
        if (StringUtils.hasText(this.url) && !this.url.startsWith("http")) {
            this.url = "http://" + this.url;
        }
        String url = this.url + cleanPath();
        Client client = getOptional(context, Client.class);
        if (client != null) {
            if (client instanceof LoadBalancerFeignClient) {
                // not lod balancing because we have a url,
                // but ribbon is on the classpath, so unwrap
                client = ((LoadBalancerFeignClient)client).getDelegate();
            }
            builder.client(client);
        }
        Targeter targeter = get(context, Targeter.class);
        return targeter.target(this, builder, context, new HardCodedTarget<>(
                this.type, this.name, url));
    }

1. 获取bean:FeignContext，这个bean上篇文章已经说过了。里面包含了各个Feign客户端的配置

2. 构建Feign.Builder

设置编解码器

    protected Feign.Builder feign(FeignContext context) {
        FeignLoggerFactory loggerFactory = get(context, FeignLoggerFactory.class);
        Logger logger = loggerFactory.create(this.type);

        Feign.Builder builder = get(context, Feign.Builder.class)
                .logger(logger)
                .encoder(get(context, Encoder.class))
                .decoder(get(context, Decoder.class))
                .contract(get(context, Contract.class));
        configureFeign(context, builder);

        return builder;
    }

设置日志、重试策略、错误code解析、超时时间、拦截器

    protected void configureUsingConfiguration(FeignContext context, Feign.Builder builder) {
        Logger.Level level = getOptional(context, Logger.Level.class);
        if (level != null) {
            builder.logLevel(level);
        }
        Retryer retryer = getOptional(context, Retryer.class);
        if (retryer != null) {
            builder.retryer(retryer);
        }
        ErrorDecoder errorDecoder = getOptional(context, ErrorDecoder.class);
        if (errorDecoder != null) {
            builder.errorDecoder(errorDecoder);
        }
        Request.Options options = getOptional(context, Request.Options.class);
        if (options != null) {
            builder.options(options);
        }
        Map requestInterceptors = context.getInstances(
                this.name, RequestInterceptor.class);
        if (requestInterceptors != null) {
            builder.requestInterceptors(requestInterceptors.values());
        }

        if (decode404) {
            builder.decode404();
        }
    }

1. 判断Feign是否指定url属性，正常情况下是没有指定url的，所以会添加一个http://前缀

4. 获取代理

protected  T loadBalance(Feign.Builder builder, FeignContext context,
                            HardCodedTarget target) {

    Client client = getOptional(context, Client.class);
    if (client != null) {
        builder.client(client);
        Targeter targeter = get(context, Targeter.class);

        return targeter.target(this, builder, context, target);
    }

    throw new IllegalStateException(
                "No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-netflix-ribbon?");
}

首先获取Client的实现类，这个实现类是LoadBalancerFeignClient,这个类里融合了Ribbon的相关内容。然后将Client包装到Feign.Builder中，接着获取Targeter，这里我们存在Hystrix环境，所以Targeter的实现类为HystrixTargeter

    public  T target(FeignClientFactoryBean factory, Feign.Builder feign, FeignContext context,
                        Target.HardCodedTarget target) {
        if (!(feign instanceof feign.hystrix.HystrixFeign.Builder)) {
            return feign.target(target);
        }
        feign.hystrix.HystrixFeign.Builder builder = (feign.hystrix.HystrixFeign.Builder) feign;
        SetterFactory setterFactory = getOptional(factory.getName(), context,
            SetterFactory.class);
        if (setterFactory != null) {
            builder.setterFactory(setterFactory);
        }
        Class fallback = factory.getFallback();
        if (fallback != void.class) {
            return targetWithFallback(factory.getName(), context, target, builder, fallback);
        }
        Class fallbackFactory = factory.getFallbackFactory();
        if (fallbackFactory != void.class) {
            return targetWithFallbackFactory(factory.getName(), context, target, builder, fallbackFactory);
        }

        return feign.target(target);
    }

接着以Feign客户端设置了fallback为例

    private  T targetWithFallback(String feignClientName, FeignContext context,Target.HardCodedTarget target,HystrixFeign.Builder builder, Class fallback) {
        T fallbackInstance = getFromContext("fallback", feignClientName, context, fallback, target.type());
        return builder.target(target, fallbackInstance);
    }

接着就是这个代理的创建，现在这个代理中包含了Ribbon和Hystrix。而这个代理类的实现类是HystrixInvocationHandler

  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