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本文主要研究一下spring cloud的LoadBalancerAutoConfiguration

RibbonAutoConfiguration

spring-cloud-netflix-ribbon-2.0.0.RC2-sources.jar!/org/springframework/cloud/netflix/ribbon/RibbonAutoConfiguration.java

@Configuration
@ConditionalOnClass(RestTemplate.class)
@ConditionalOnBean(LoadBalancerClient.class)
@EnableConfigurationProperties(LoadBalancerRetryProperties.class)
public class LoadBalancerAutoConfiguration {@LoadBalanced@Autowired(required = false)private List<RestTemplate> restTemplates = Collections.emptyList();@Beanpublic SmartInitializingSingleton loadBalancedRestTemplateInitializerDeprecated(final ObjectProvider<List<RestTemplateCustomizer>> restTemplateCustomizers) {return () -> restTemplateCustomizers.ifAvailable(customizers -> {for (RestTemplate restTemplate : LoadBalancerAutoConfiguration.this.restTemplates) {for (RestTemplateCustomizer customizer : customizers) {customizer.customize(restTemplate);}}});}@Autowired(required = false)private List<LoadBalancerRequestTransformer> transformers = Collections.emptyList();@Bean@ConditionalOnMissingBeanpublic LoadBalancerRequestFactory loadBalancerRequestFactory(LoadBalancerClient loadBalancerClient) {return new LoadBalancerRequestFactory(loadBalancerClient, transformers);}@Configuration@ConditionalOnMissingClass("org.springframework.retry.support.RetryTemplate")static class LoadBalancerInterceptorConfig {@Beanpublic LoadBalancerInterceptor ribbonInterceptor(LoadBalancerClient loadBalancerClient,LoadBalancerRequestFactory requestFactory) {return new LoadBalancerInterceptor(loadBalancerClient, requestFactory);}@Bean@ConditionalOnMissingBeanpublic RestTemplateCustomizer restTemplateCustomizer(final LoadBalancerInterceptor loadBalancerInterceptor) {return restTemplate -> {List<ClientHttpRequestInterceptor> list = new ArrayList<>(restTemplate.getInterceptors());list.add(loadBalancerInterceptor);restTemplate.setInterceptors(list);};}}@Configuration@ConditionalOnClass(RetryTemplate.class)public static class RetryAutoConfiguration {@Bean@ConditionalOnMissingBeanpublic LoadBalancedRetryFactory loadBalancedRetryFactory() {return new LoadBalancedRetryFactory() {};}}@Configuration@ConditionalOnClass(RetryTemplate.class)public static class RetryInterceptorAutoConfiguration {@Bean@ConditionalOnMissingBeanpublic RetryLoadBalancerInterceptor ribbonInterceptor(LoadBalancerClient loadBalancerClient, LoadBalancerRetryProperties properties,LoadBalancerRequestFactory requestFactory,LoadBalancedRetryFactory loadBalancedRetryFactory) {return new RetryLoadBalancerInterceptor(loadBalancerClient, properties,requestFactory, loadBalancedRetryFactory);}@Bean@ConditionalOnMissingBeanpublic RestTemplateCustomizer restTemplateCustomizer(final RetryLoadBalancerInterceptor loadBalancerInterceptor) {return restTemplate -> {List<ClientHttpRequestInterceptor> list = new ArrayList<>(restTemplate.getInterceptors());list.add(loadBalancerInterceptor);restTemplate.setInterceptors(list);};}}
}
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• 定义了LoadBalancerRequestFactory以及LoadBalancerInterceptorConfig、RetryAutoConfiguration、RetryInterceptorAutoConfiguration

LoadBalancerRetryProperties

spring-cloud-commons-2.0.0.RC2-sources.jar!/org/springframework/cloud/client/loadbalancer/LoadBalancerRetryProperties.java

/*** Configuration properties for the {@link LoadBalancerClient}.* @author Ryan Baxter*/
@ConfigurationProperties("spring.cloud.loadbalancer.retry")
public class LoadBalancerRetryProperties {private boolean enabled = true;/*** Returns true if the load balancer should retry failed requests.* @return true if the load balancer should retry failed request, false otherwise.*/public boolean isEnabled() {return enabled;}/*** Sets whether the load balancer should retry failed request.* @param enabled whether the load balancer should retry failed requests*/public void setEnabled(boolean enabled) {this.enabled = enabled;}
}
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• 这个配置是否开启loadbalancer的retry

RetryLoadBalancerInterceptor

spring-cloud-commons-2.0.0.RC2-sources.jar!/org/springframework/cloud/client/loadbalancer/RetryLoadBalancerInterceptor.java

public class RetryLoadBalancerInterceptor implements ClientHttpRequestInterceptor {private LoadBalancerClient loadBalancer;private LoadBalancerRetryProperties lbProperties;private LoadBalancerRequestFactory requestFactory;private LoadBalancedRetryFactory lbRetryFactory;public RetryLoadBalancerInterceptor(LoadBalancerClient loadBalancer,LoadBalancerRetryProperties lbProperties,LoadBalancerRequestFactory requestFactory,LoadBalancedRetryFactory lbRetryFactory) {this.loadBalancer = loadBalancer;this.lbProperties = lbProperties;this.requestFactory = requestFactory;this.lbRetryFactory = lbRetryFactory;}@Overridepublic ClientHttpResponse intercept(final HttpRequest request, final byte[] body,final ClientHttpRequestExecution execution) throws IOException {final URI originalUri = request.getURI();final String serviceName = originalUri.getHost();Assert.state(serviceName != null, "Request URI does not contain a valid hostname: " + originalUri);final LoadBalancedRetryPolicy retryPolicy = lbRetryFactory.createRetryPolicy(serviceName,loadBalancer);RetryTemplate template = createRetryTemplate(serviceName, request, retryPolicy);return template.execute(context -> {ServiceInstance serviceInstance = null;if (context instanceof LoadBalancedRetryContext) {LoadBalancedRetryContext lbContext = (LoadBalancedRetryContext) context;serviceInstance = lbContext.getServiceInstance();}if (serviceInstance == null) {serviceInstance = loadBalancer.choose(serviceName);}ClientHttpResponse response = RetryLoadBalancerInterceptor.this.loadBalancer.execute(serviceName, serviceInstance,requestFactory.createRequest(request, body, execution));int statusCode = response.getRawStatusCode();if (retryPolicy != null && retryPolicy.retryableStatusCode(statusCode)) {byte[] bodyCopy = StreamUtils.copyToByteArray(response.getBody());response.close();throw new ClientHttpResponseStatusCodeException(serviceName, response, bodyCopy);}return response;}, new LoadBalancedRecoveryCallback<ClientHttpResponse, ClientHttpResponse>() {//This is a special case, where both parameters to LoadBalancedRecoveryCallback are//the same.  In most cases they would be different.@Overrideprotected ClientHttpResponse createResponse(ClientHttpResponse response, URI uri) {return response;}});}private RetryTemplate createRetryTemplate(String serviceName, HttpRequest request, LoadBalancedRetryPolicy retryPolicy) {RetryTemplate template = new RetryTemplate();BackOffPolicy backOffPolicy = lbRetryFactory.createBackOffPolicy(serviceName);template.setBackOffPolicy(backOffPolicy == null ? new NoBackOffPolicy() : backOffPolicy);template.setThrowLastExceptionOnExhausted(true);RetryListener[] retryListeners = lbRetryFactory.createRetryListeners(serviceName);if (retryListeners != null && retryListeners.length != 0) {template.setListeners(retryListeners);}template.setRetryPolicy(!lbProperties.isEnabled() || retryPolicy == null ? new NeverRetryPolicy(): new InterceptorRetryPolicy(request, retryPolicy, loadBalancer,serviceName));return template;}
}
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• 实现了ClientHttpRequestInterceptor接口
• 通过lbRetryFactory.createRetryPolicy(serviceName,loadBalancer)创建重试策略，然后创建RetryTemplate

小结

LoadBalancerAutoConfiguration这个类定义了LoadBalancerRequestFactory以及LoadBalancerInterceptor，另外主要配置的是loadBalancer的重试。重试功能主要通过spring retry组件的RetryTemplate来实现。

doc

• Spring Cloud Finchley.RELEASE Documentation