FeignClient如何确定通过ApacheHttpClient、FeignBlockingLoadBalancerClient、RetryableFeignBlockingLoadBalancer

柔光的暖阳◎ 2022-11-17 05:27 151阅读 0赞

> springcloud使用feign时对feignclient的初始化核心在FeignClientsRegistrar类中，FeignClientsRegistrar类中会对FeignClientFactoryBean类进行初始化；

##### 一、先看下FeignClientsRegistrar\#registerFeignClient方法 #####

private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata,
    			Map<String, Object> attributes) { 
    		String className = annotationMetadata.getClassName();
    		Class clazz = ClassUtils.resolveClassName(className, null);
    		ConfigurableBeanFactory beanFactory = registry instanceof ConfigurableBeanFactory
    				? (ConfigurableBeanFactory) registry : null;
    		String contextId = getContextId(beanFactory, attributes);
    		String name = getName(attributes);
        //实例化FeignClientFactoryBean工厂
    		FeignClientFactoryBean factoryBean = new FeignClientFactoryBean();
    		factoryBean.setBeanFactory(beanFactory);
    		factoryBean.setName(name);
    		factoryBean.setContextId(contextId);
    		factoryBean.setType(clazz);
        //实例化BeanDefinition构建器，在注入容器时会回调lambda表达式
    		BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(clazz, () -> { 
          //设置@FeignClient注解设置的url
    			factoryBean.setUrl(getUrl(beanFactory, attributes));
          //设置@FeignClient注解上path属性
    			factoryBean.setPath(getPath(beanFactory, attributes));
    			factoryBean.setDecode404(Boolean.parseBoolean(String.valueOf(attributes.get("decode404"))));
    			Object fallback = attributes.get("fallback");
    			if (fallback != null) { 
    				factoryBean.setFallback(fallback instanceof Class ? (Class<?>) fallback
    						: ClassUtils.resolveClassName(fallback.toString(), null));
    			}
    			Object fallbackFactory = attributes.get("fallbackFactory");
    			if (fallbackFactory != null) { 
    				factoryBean.setFallbackFactory(fallbackFactory instanceof Class ? (Class<?>) fallbackFactory
    						: ClassUtils.resolveClassName(fallbackFactory.toString(), null));
    			}
          //调用工厂的getObject方法
    			return factoryBean.getObject();
    		});
    		definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
    		definition.setLazyInit(true);
    		validate(attributes);
    
    		AbstractBeanDefinition beanDefinition = definition.getBeanDefinition();
    		beanDefinition.setAttribute(FactoryBean.OBJECT_TYPE_ATTRIBUTE, className);
    		beanDefinition.setAttribute("feignClientsRegistrarFactoryBean", factoryBean);
    
    		// has a default, won't be null
    		boolean primary = (Boolean) attributes.get("primary");
    
    		beanDefinition.setPrimary(primary);
    
    		String[] qualifiers = getQualifiers(attributes);
    		if (ObjectUtils.isEmpty(qualifiers)) { 
    			qualifiers = new String[] {  contextId + "FeignClient" };
    		}
    
    		BeanDefinitionHolder holder = new BeanDefinitionHolder(beanDefinition, className, qualifiers);
        //将FeignClientFactoryBean实例注入容器之中
    		BeanDefinitionReaderUtils.registerBeanDefinition(holder, registry);
    	}

上述代码在将FeignClientFactoryBean实例注入容器时后会调用FeignClientFactoryBean类的getObject方法；

##### 二、org.springframework.cloud.openfeign.FeignClientFactoryBean\#getObject方法 #####

@Override
    	public Object getObject() { 
    		return getTarget();
    	}

##### 三、org.springframework.cloud.openfeign.FeignClientFactoryBean\#getTarget方法是确定请求调用哪个client的核心 #####

<T> T getTarget() { 
    		FeignContext context = beanFactory != null ? beanFactory.getBean(FeignContext.class)
    				: applicationContext.getBean(FeignContext.class);
    		Feign.Builder builder = feign(context);
    		//微服务@FeignClient的url为null,则会执行如下代码
    		if (!StringUtils.hasText(url)) { 
    			if (!name.startsWith("http")) { 
    				url = "http://" + name;
    			}
    			else { 
    				url = name;
    			}
    			url += cleanPath();
          // 此处调用feign.Feign.Builder#target(feign.Target<T>)
          //构建ReflectiveFeign对象
          //构建AOP切面请求代理
    			return (T) loadBalance(builder, context, new HardCodedTarget<>(type, name, url));
    		}
        //非微服务@FeignClient的url为非空，则执行如下代码
    		if (StringUtils.hasText(url) && !url.startsWith("http")) { 
    			url = "http://" + url;
    		}
    		String url = this.url + cleanPath();
        //获取上下文中的Client对象
    		Client client = getOptional(context, Client.class);
    		if (client != null) { 
    			if (client instanceof FeignBlockingLoadBalancerClient) { 
    				// 非load balancing，因为存在url
    				// 获取FeignBlockingLoadBalancerClient的代理，即AppacheHttpClient
    				client = ((FeignBlockingLoadBalancerClient) client).getDelegate();
    			}
    			if (client instanceof RetryableFeignBlockingLoadBalancerClient) { 
    				// 非load balancing，因为存在url
    				// 获取FeignBlockingLoadBalancerClient的代理，即AppacheHttpClient
    				client = ((RetryableFeignBlockingLoadBalancerClient) client).getDelegate();
    			}
          //初始化构造器为AppacheHttpClient
    			builder.client(client);
    		}
    		Targeter targeter = get(context, Targeter.class);
          // 此处调用feign.Feign.Builder#target(feign.Target<T>)
          //构建ReflectiveFeign对象
          //构建AOP切面请求代理
    		return (T) targeter.target(this, builder, context, new HardCodedTarget<>(type, name, url));
    	}

org.springframework.cloud.openfeign.FeignClientFactoryBean\#loadBalance方法获取loadBalance客户端

protected <T> T loadBalance(Feign.Builder builder, FeignContext context, HardCodedTarget<T> target) { 
        //获取微服务请求的FeignBlockingLoadBalancerClient或RetryableFeignBlockingLoadBalancerClient
    		Client client = getOptional(context, Client.class);
    		if (client != null) { 
          //初始化构造器的Client对象
    			builder.client(client);
    			Targeter targeter = get(context, Targeter.class);
          // 此处调用feign.Feign.Builder#target(feign.Target<T>)
          //构建ReflectiveFeign对象
          //构建AOP切面请求代理
    			return targeter.target(this, builder, context, target);
    		}
    
    		throw new IllegalStateException(
    				"No Feign Client for loadBalancing defined. Did you forget to include spring-cloud-starter-loadbalancer?");
    	}

> 经上述代码分析可知@FeignClient注解的url为空时，client为loadbalancer微服务对象，其Client对象是FeignBlockingLoadBalancerClient、RetryableFeignBlockingLoadBalancerClient；而url为非空时为普通请求，则Client对象是ApacheHttpClient实例对象，其获取ApacheHttpClient对象是通过getDelegate方法获取，这又是为何呢？

@Configuration(proxyBeanMethods = false)
    @ConditionalOnClass(ApacheHttpClient.class)
    @ConditionalOnBean({  LoadBalancerClient.class, LoadBalancerClientFactory.class })
    @ConditionalOnProperty(value = "feign.httpclient.enabled", matchIfMissing = true)
    @Conditional(HttpClient5DisabledConditions.class)
    @Import(HttpClientFeignConfiguration.class)
    @EnableConfigurationProperties(LoadBalancerProperties.class)
    class HttpClientFeignLoadBalancerConfiguration { 
    
    	@Bean
    	@ConditionalOnMissingBean
    	@Conditional(OnRetryNotEnabledCondition.class)
    	public Client feignClient(LoadBalancerClient loadBalancerClient, HttpClient httpClient,
    			LoadBalancerProperties properties, LoadBalancerClientFactory loadBalancerClientFactory) { 
    		ApacheHttpClient delegate = new ApacheHttpClient(httpClient);
        //未开启重试实例对象，代理是ApacheHttpClient
    		return new FeignBlockingLoadBalancerClient(delegate, loadBalancerClient, properties, loadBalancerClientFactory);
    	}
    
    	@Bean
    	@ConditionalOnMissingBean
    	@ConditionalOnClass(name = "org.springframework.retry.support.RetryTemplate")
    	@ConditionalOnBean(LoadBalancedRetryFactory.class)
    	@ConditionalOnProperty(value = "spring.cloud.loadbalancer.retry.enabled", havingValue = "true",
    			matchIfMissing = true)
    	public Client feignRetryClient(LoadBalancerClient loadBalancerClient, HttpClient httpClient,
    			LoadBalancedRetryFactory loadBalancedRetryFactory, LoadBalancerProperties properties,
    			LoadBalancerClientFactory loadBalancerClientFactory) { 
    		ApacheHttpClient delegate = new ApacheHttpClient(httpClient);
        //开启重试实例化对象，代理为ApacheHttpClient
    		return new RetryableFeignBlockingLoadBalancerClient(delegate, loadBalancerClient, loadBalancedRetryFactory,
    				properties, loadBalancerClientFactory);
    	}
    
    }

GitHub地址：[https://github.com/mingyang66/spring-parent][https_github.com_mingyang66_spring-parent]

[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent