/** * Annotation to mark a RestTemplate bean to be configured to use a LoadBalancerClient * @author Spencer Gibb */@Target({ ElementType.FIELD, ElementType.PARAMETER, ElementType.METHOD })@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@Qualifierpublic @interface LoadBalanced {}

/** * Represents a client side load balancer * @author Spencer Gibb */public interface LoadBalancerClient extends ServiceInstanceChooser {	/**	 * execute request using a ServiceInstance from the LoadBalancer for the specified	 * service	 * @param serviceId the service id to look up the LoadBalancer	 * @param request allows implementations to execute pre and post actions such as	 * incrementing metrics	 * @return the result of the LoadBalancerRequest callback on the selected	 * ServiceInstance	 */	<T> T execute(String serviceId, LoadBalancerRequest<T> request) throws IOException;	/**	 * execute request using a ServiceInstance from the LoadBalancer for the specified	 * service	 * @param serviceId the service id to look up the LoadBalancer	 * @param serviceInstance the service to execute the request to	 * @param request allows implementations to execute pre and post actions such as	 * incrementing metrics	 * @return the result of the LoadBalancerRequest callback on the selected	 * ServiceInstance	 */	<T> T execute(String serviceId, ServiceInstance serviceInstance, LoadBalancerRequest<T> request) throws IOException;	/**	 * Create a proper URI with a real host and port for systems to utilize.	 * Some systems use a URI with the logical serivce name as the host,	 * such as http://myservice/path/to/service.  This will replace the	 * service name with the host:port from the ServiceInstance.	 * @param instance	 * @param original a URI with the host as a logical service name	 * @return a reconstructed URI	 */	URI reconstructURI(ServiceInstance instance, URI original);}

public interface ServiceInstanceChooser {    /**     * Choose a ServiceInstance from the LoadBalancer for the specified service     * @param serviceId the service id to look up the LoadBalancer     * @return a ServiceInstance that matches the serviceId     */    ServiceInstance choose(String serviceId);}

/** * Auto configuration for Ribbon (client side load balancing). * * @author Spencer Gibb * @author Dave Syer * @author Will Tran */@Configuration@ConditionalOnClass(RestTemplate.class) //条件 : RestTemplate必须在工程的类路径下@ConditionalOnBean(LoadBalancerClient.class)  //条件: Spring 容器中必须包含LoadBalancerClient的实现，即RibbonLoadBalancerClient@EnableConfigurationProperties(LoadBalancerRetryProperties.class) //启动重试功能，可以spring.cloud.loadbalancer.retry=false,取消重试，默认参数为truepublic class LoadBalancerAutoConfiguration {	@LoadBalanced	@Autowired(required = false)	private List<RestTemplate> restTemplates = Collections.emptyList(); //维护一个RestTemplate列表，通过LoadBalanced来注解。	@Bean	public SmartInitializingSingleton loadBalancedRestTemplateInitializer( //加载初始话自定义的restTeplate,实质是初始化InterceptingHttpAccessor具体调用			final List<RestTemplateCustomizer> customizers) {		return new SmartInitializingSingleton() {			@Override			public void afterSingletonsInstantiated() {				for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {					for (RestTemplateCustomizer customizer : customizers) {						customizer.customize(restTemplate);					}				}			}		};	}	@Autowired(required = false)	private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();	@Bean	@ConditionalOnMissingBean	public LoadBalancerRequestFactory loadBalancerRequestFactory(			LoadBalancerClient loadBalancerClient) {		return new LoadBalancerRequestFactory(loadBalancerClient, transformers);	}	@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);				}			};		}	}	@Configuration	@ConditionalOnClass(RetryTemplate.class)	static class RetryAutoConfiguration {		@Bean		public RetryTemplate retryTemplate() {			RetryTemplate template =  new RetryTemplate();			template.setThrowLastExceptionOnExhausted(true);			return template;		}		@Bean		@ConditionalOnMissingBean		public LoadBalancedRetryPolicyFactory loadBalancedRetryPolicyFactory() {			return new LoadBalancedRetryPolicyFactory.NeverRetryFactory();		}		@Bean		public RetryLoadBalancerInterceptor ribbonInterceptor(				LoadBalancerClient loadBalancerClient, LoadBalancerRetryProperties properties,				LoadBalancedRetryPolicyFactory lbRetryPolicyFactory,				LoadBalancerRequestFactory requestFactory) {			return new RetryLoadBalancerInterceptor(loadBalancerClient, retryTemplate(), properties,					lbRetryPolicyFactory, requestFactory);		}		@Bean		@ConditionalOnMissingBean		public RestTemplateCustomizer restTemplateCustomizer( //自定义RestTemplate ,实质是初始化InterceptingHttpAccessor				final RetryLoadBalancerInterceptor loadBalancerInterceptor) {			return new RestTemplateCustomizer() {				@Override				public void customize(RestTemplate restTemplate) {					List<ClientHttpRequestInterceptor> list = new ArrayList<>(							restTemplate.getInterceptors());					list.add(loadBalancerInterceptor);					restTemplate.setInterceptors(list);				}			};		}	}}