Spring Cloud 客服端负载均衡 Ribbon

/**

 * 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true

public 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);

                }

            };

        }

    }

}