詳解openfeign集成spring?cloud?loadbalancer實現(xiàn)負載均衡流程

更新時間：2023年07月06日 09:45:07 作者：子瞻

這篇文章主要介紹了openfeign集成spring?cloud?loadbalancer實現(xiàn)負載均衡流程詳解，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進步，早日升職加薪

Feignclient負載均衡中如何起作用

當我們在項目中調(diào)用自己實現(xiàn)的Feignclient負載均衡中如何起作用？請看下圖：

圖一

在圖一中我們可以發(fā)現(xiàn)，在ConsumerController中調(diào)用自定義的DemoFeignClient方法時，通過spring容器中對DemoFeignclient的代理類的調(diào)用最終通過feign.SynchronousMethodHandler.invoke()->openfeign.loadbalancer.execute()->org.springframework.cloud.loadbalancer.blocking.client.FeignBlockingLoadBalancerClient.choose()->org.springframework.cloud.loadbalancer.core.RoundRobinLoadBalancer.choose()這樣的調(diào)用鏈，最終執(zhí)行spring cloud loadbalaner中的輪詢負載均橫策略！

然而，上圖中的這些關(guān)鍵類是如何組合起來發(fā)揮作用呢？請我們一起繼續(xù)分析！spring cloud項目啟動后，spring容器解析并加載LoadBalancerClientConfiguration.java配置文件（如下圖所示）

圖二

然后將"reactorServiceInstanceLoadBalancer"注冊到beanDefinitionMap中。
然后會掃描我們聲明的controller,因為conroller中注入了DemoFeignClient，因此spring容器會遞歸創(chuàng)建DemoFeignClient，創(chuàng)建DemoFiegnClient過程中會通過AbstractAutowireCapableBeanFactory.obtainFromSupplier()注入instanceSupplier實例,也就是FeignClientFactoryBean實例！

主要邏輯

下面是org.springframework.cloud.openfeign.FeignClientsRegistrar.registerFeignClient()方法主要邏輯：

private void registerFeignClient(BeanDefinitionRegistry registry, AnnotationMetadata annotationMetadata,
            Map&lt;String, Object&gt; attributes) {
          //忽略非核心代碼片段
            BeanDefinitionBuilder definition = BeanDefinitionBuilder.genericBeanDefinition(clazz, () -&gt; {
            //設(shè)置url
            factoryBean.setUrl(getUrl(beanFactory, attributes));
            //設(shè)置路徑
            factoryBean.setPath(getPath(beanFactory, attributes));
            //decode404 布爾值            factoryBean.setDecode404(Boolean.parseBoolean(String.valueOf(attributes.get("decode404"))));
            Object fallback = attributes.get("fallback");
            //設(shè)置fallback
            if (fallback != null) {
                factoryBean.setFallback(fallback instanceof Class ? (Class&lt;?&gt;) fallback
                        : ClassUtils.resolveClassName(fallback.toString(), null));
            }
            //設(shè)置fallback工廠類
            Object fallbackFactory = attributes.get("fallbackFactory");
            if (fallbackFactory != null) {
                factoryBean.setFallbackFactory(fallbackFactory instanceof Class ? (Class&lt;?&gt;) fallbackFactory
                        : ClassUtils.resolveClassName(fallbackFactory.toString(), null));
            }
            //實例化我們聲明的DemoClient
            return factoryBean.getObject();
        });
}

這還沒有完，org.springframework.cloud.openfeign.FeignClientFactoryBean.getObject()中最終執(zhí)行l(wèi)oadBalance()；在loadBalance()中實例化FeignInvocationHandler;

調(diào)用DemoFeignClient中方法

在項目啟動成功之后，我們調(diào)用DemoFeignClient中的方法時

圖三

通過圖三可以發(fā)現(xiàn)，描述DemoFeignClient的RootBeanDefinition的類中還有一個叫“instanceSupplier”的類型屬性，它的值是“FeignClientsRegistrar$lambda”，那么這個類時什么時候被注入進來的呢？答案就是上面分析項目啟動過程中spring容器根據(jù)RootBeanDefinition對DemoFeignClient的描述，通過對"FeignClientsRegistrar$lambda"的調(diào)用完成對DemoFeignClient實例的創(chuàng)建。

在完成創(chuàng)建DemoFeignClient實例后，我們調(diào)用org.springframework.cloud.openfeign.loadbalancer。

FeignBlockingLoadBalancerClient.execute()執(zhí)行負載均衡策略時，執(zhí)行到如下代碼塊

Set<LoadBalancerLifecycle> supportedLifecycleProcessors = LoadBalancerLifecycleValidator
                .getSupportedLifecycleProcessors(
                        loadBalancerClientFactory.getInstances(serviceId, LoadBalancerLifecycle.class),
                        RequestDataContext.class, ResponseData.class, ServiceInstance.class);

"loadBalancerClientFactory.getInstances(serviceId, LoadBalancerLifecycle.class)"邏輯會獲取LoadBalancer實例，最終調(diào)用LoadBalancerClientConfiguration.java中的reactorServiceInstanceLoadBalancer()實現(xiàn)創(chuàng)建負載均衡實例邏輯

@Bean
    @ConditionalOnMissingBean
    public ReactorLoadBalancer<ServiceInstance> reactorServiceInstanceLoadBalancer(Environment environment,
            LoadBalancerClientFactory loadBalancerClientFactory) {
        String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
        //創(chuàng)建負載均衡實例，而且我們發(fā)現(xiàn)默認的負載均衡實例是輪詢負載均衡實例
        return new RoundRobinLoadBalancer(
                loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name);
    }

ok，截止到目前為止，我們的負載均衡實例已經(jīng)創(chuàng)建完成！

這樣一來，我們通過openfeign進行遠程調(diào)用時，通過下圖的調(diào)用鏈

圖四

FeignInvocationHandler.invoke()->SynchronousMethodHandler.invoke()->org.springframework.cloud.openfeign.loadbalancer.FeignBlockingLoadBalancerClient.execute()->org.springframework.cloud.loadbalancer.blocking.client.BlockingLoadBalancerClient.choose()->org.springframework.cloud.loadbalancer.core.RoundRobinLoadBalancer.choose(),這樣的調(diào)用鏈最終根據(jù)RoundRobinLoadBalancer.choose()獲取服務實例。

public Mono<Response<ServiceInstance>> choose(Request request) {
        ServiceInstanceListSupplier supplier = serviceInstanceListSupplierProvider
                .getIfAvailable(NoopServiceInstanceListSupplier::new);
        //返回服務實例
        return supplier.get(request).next()
                .map(serviceInstances -> processInstanceResponse(supplier, serviceInstances));
    }

拿到服務實例后，F(xiàn)eignBlockingLoadBalancerClient.execute()中最終通過LoadBalancerUtils.executeWithLoadBalancerLifecycleProcessing()獲取響應結(jié)果！

下面是具體代碼邏輯：

static Response executeWithLoadBalancerLifecycleProcessing(Client feignClient, Request.Options options,
            Request feignRequest, org.springframework.cloud.client.loadbalancer.Request lbRequest,
            org.springframework.cloud.client.loadbalancer.Response<ServiceInstance> lbResponse,
            Set<LoadBalancerLifecycle> supportedLifecycleProcessors, boolean loadBalanced, boolean useRawStatusCodes)
            throws IOException {
        supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onStartRequest(lbRequest, lbResponse));
        try {
            //通過openfeign調(diào)用，獲取響應結(jié)果
            Response response = feignClient.execute(feignRequest, options);
            if (loadBalanced) {
                supportedLifecycleProcessors.forEach(
                        lifecycle -> lifecycle.onComplete(new CompletionContext<>(CompletionContext.Status.SUCCESS,
                                lbRequest, lbResponse, buildResponseData(response, useRawStatusCodes))));
            }
            return response;
        }
        catch (Exception exception) {
            if (loadBalanced) {
                supportedLifecycleProcessors.forEach(lifecycle -> lifecycle.onComplete(
                        new CompletionContext<>(CompletionContext.Status.FAILED, exception, lbRequest, lbResponse)));
            }
            throw exception;
        }
    }

以上就是詳解openfeign集成spring cloud loadbalancer實現(xiàn)負載均衡流程的詳細內(nèi)容，更多關(guān)于spring cloud loadbalancer的資料請關(guān)注腳本之家其它相關(guān)文章！

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