关于java:SpringCloud-Ribbon-部分源码

1：ribbon是提供通过serviceId拜访服务的能力，而且提供了负载平衡能力。在springcloud外面，有2个主动配置加载类 LoadBalancerAutoConfiguration 和 RibbonAutoConfiguration。LoadBalancerAutoConfiguration次要实现对 RestTemplate 对象的负载平衡拜访，RibbonAutoConfiguration次要是对Ribbon所需组件的实例化。别离在springcloud-common 和 netflix-core 的 spring.foctories 文件里。

org.springframework.boot.autoconfigure.EnableAutoConfiguration=
org.springframework.cloud.netflix.hystrix.HystrixAutoConfiguration,
org.springframework.cloud.netflix.hystrix.security.HystrixSecurityAutoConfiguration,
org.springframework.cloud.netflix.ribbon.RibbonAutoConfiguration,
org.springframework.cloud.netflix.rx.RxJavaAutoConfiguration,

org.springframework.boot.autoconfigure.EnableAutoConfiguration=
org.springframework.cloud.client.CommonsClientAutoConfiguration,
org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration,
org.springframework.cloud.client.serviceregistry.ServiceRegistryAutoConfiguration, 

2：RibbonAutoConfiguration 次要是对Ribbon组件的实例化，其对应关系是：
IClientConfig –> DefaultClientConfigImpl
IRule –> ZoneAvoidanceRule
IPing –> DummyPing
ServerList –> ConfigurationBasedServerList
ServerListUpdater –> PollingServerListUpdater
ILoadBalancer –> ZoneAwareLoadBalancer
LoadBalancerClient –> RibbonLoadBalancerClient
同时，也会创立：SpringClientFactory 对象。

3：LoadBalancerAutoConfiguration 次要是对 RestTemplate 进行负载平衡配置。 其次要实现是创立拦截器 LoadBalancerInterceptor。而后对 RestTemplate 进行自定义配置，代码如下：

@Bean
    public SmartInitializingSingleton loadBalancedRestTemplateInitializer(
            final List<RestTemplateCustomizer> customizers) {
        return new SmartInitializingSingleton() {
            @Override
            public void afterSingletonsInstantiated() {
                for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {
                    for (RestTemplateCustomizer customizer : customizers) {
                        customizer.customize(restTemplate);
                    }
                }
            }
        };
    }
@Configuration
    @ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")
    static class LoadBalancerInterceptorConfig {
        @Bean
        public LoadBalancerInterceptor ribbonInterceptor(
                LoadBalancerClient loadBalancerClient,
                LoadBalancerRequestFactory requestFactory) {
            return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);
        }

        @Bean
        @ConditionalOnMissingBean
        public RestTemplateCustomizer restTemplateCustomizer(
                final LoadBalancerInterceptor loadBalancerInterceptor) {
            return new RestTemplateCustomizer() {
                @Override
                public void customize(RestTemplate restTemplate) {
                    List<ClientHttpRequestInterceptor> list = new ArrayList<>(
                            restTemplate.getInterceptors());
                    list.add(loadBalancerInterceptor);
                    restTemplate.setInterceptors(list);
                }
            };
        }
    } 

在下面的代码中，减少的拦截器类是：LoadBalancerInterceptor。 LoadBalancerClient 接口的实现类是：RibbonLoadBalancerClient。

4：在应用 RestTemplate 进行 POST， GET 申请的时候，最终执行的是 办法：LoadBalancerInterceptor#intercept。 在该办法里，调用办法：RibbonLoadBalancerClient#execute(String, LoadBalancerRequest<T>)

@Override
    public ClientHttpResponse intercept(final HttpRequest request, final byte[] body,
            final ClientHttpRequestExecution execution) throws IOException {
        final URI originalUri = request.getURI();
        String serviceName = originalUri.getHost();
        Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);
        return this.loadBalancer.execute(serviceName, requestFactory.createRequest(request, body, execution));
    } 

5：在 execute 办法里，次要是 获取到负载均衡器，获取服务提供者的拜访门路，拜访

@Override
    public <T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException {
        ILoadBalancer loadBalancer = getLoadBalancer(serviceId);  //获取负载均衡器
        Server server = getServer(loadBalancer);  //获取服务拜访门路，包含IP端口
        if (server == null) {
            throw new IllegalStateException("No instances available for " + serviceId);
        }
        RibbonServer ribbonServer = new RibbonServer(serviceId, server, isSecure(server,
                serviceId), serverIntrospector(serviceId).getMetadata(server));

        return execute(serviceId, ribbonServer, request); //拜访服务
    } 

6：在 SpringClientFactory#getLoadBalancer 里，获取的是接口 ILoadBalancer 的实例。其实现是 结构Spring的上下文对象 AnnotationConfigApplicationContext， 而后加载配置类:RibbonClientConfiguration.
在RibbonClientConfiguration类里，会实例化 ZoneAwareLoadBalancer 对象。获取到 ILoadBalancer 的单例模式后，会缓存在内存外面。

public ILoadBalancer getLoadBalancer(String name) {
        return getInstance(name, ILoadBalancer.class);
    }

protected AnnotationConfigApplicationContext getContext(String name) {
        if (!this.contexts.containsKey(name)) {
            synchronized (this.contexts) {
                if (!this.contexts.containsKey(name)) {
                    this.contexts.put(name, createContext(name));
                }
            }
        }
        return this.contexts.get(name);
    }

@Bean
    @ConditionalOnMissingBean
    public ILoadBalancer ribbonLoadBalancer(IClientConfig config,
            ServerList<Server> serverList, ServerListFilter<Server> serverListFilter,
            IRule rule, IPing ping, ServerListUpdater serverListUpdater) {
        if (this.propertiesFactory.isSet(ILoadBalancer.class, name)) {
            return this.propertiesFactory.get(ILoadBalancer.class, config, name);
        }
        return new ZoneAwareLoadBalancer<>(config, rule, ping, serverList,
                serverListFilter, serverListUpdater);
    } 

7：ZoneAwareLoadBalancer 会调用 ZoneAvoidanceRule 里的 choose() 办法。 该办法外面，通过负载均衡器里，获取所有的服务节点（IRule实例里的负载均衡器是在ZoneAwareLoadBalancer 实例化的时候设置的）。lb.getAllServers() 办法获取的是获取的缓存对象 allServerList。

@Override
    public Server choose(Object key) {
        ILoadBalancer lb = getLoadBalancer();
        Optional<Server> server = getPredicate().chooseRoundRobinAfterFiltering(lb.getAllServers(), key);
        if (server.isPresent()) {
            return server.get();
        } else {
            return null;
        }       
    } 

8：获取到服务列表后，ZoneAvoidanceRule 前面 应用 chooseRoundRobinAfterFiltering() 抉择服务，按照代码，应用的是循环算法抉择 Server

public Optional<Server> chooseRoundRobinAfterFiltering(List<Server> servers, Object loadBalancerKey) {
        List<Server> eligible = getEligibleServers(servers, loadBalancerKey);
        if (eligible.size() == 0) {
            return Optional.absent();
        }
        return Optional.of(eligible.get(nextIndex.getAndIncrement() % eligible.size()));
    } 

9：选定Server对象后，外面有拜访的实例的IP和端口信息。会应用 httpClient 对象拜访对象的节点。代码如下：

public LoadBalancerRequest<ClientHttpResponse> createRequest(final HttpRequest request,
            final byte[] body, final ClientHttpRequestExecution execution) {
        return new LoadBalancerRequest<ClientHttpResponse>() {
            @Override
            public ClientHttpResponse apply(final ServiceInstance instance)
                    throws Exception {
                HttpRequest serviceRequest = new ServiceRequestWrapper(request, instance, loadBalancer);
                if (transformers != null) {
                    for (LoadBalancerRequestTransformer transformer : transformers) {
                        serviceRequest = transformer.transformRequest(serviceRequest, instance);
                    }
                }
                return execution.execute(serviceRequest, body);
            }

        };
    }