Spring-Cloud-Loadblancer详细分析_4

在RoundRobinLoadBalancer.choose中的serviceInstanceListSupplierProvider就是获取服务列表的关键，那么此对象是怎么拿到的呢，让我们回到RoundRobinLoadBalancer的创建过程

@Configuration(proxyBeanMethods = false)
@ConditionalOnDiscoveryEnabled
public class LoadBalancerClientConfiguration {private static final int REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER = 193827465;/*** 轮训的负载均衡策略*/@Bean@ConditionalOnMissingBeanpublic ReactorLoadBalancer<ServiceInstance> reactorServiceInstanceLoadBalancer(Environment environment,LoadBalancerClientFactory loadBalancerClientFactory) {String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);return new RoundRobinLoadBalancer(loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name);}/*** WebFlux环境下的ServiceInstanceListSupplier的bean*/@Configuration(proxyBeanMethods = false)@ConditionalOnReactiveDiscoveryEnabled@Order(REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER)public static class ReactiveSupportConfiguration {@Bean@ConditionalOnBean(ReactiveDiscoveryClient.class)@ConditionalOnMissingBean@Conditional(DefaultConfigurationCondition.class)public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(ConfigurableApplicationContext context) {return ServiceInstanceListSupplier.builder().withDiscoveryClient().withCaching().build(context);}//省略	}/*** web环境的ServiceInstanceListSupplier的bean*/@Configuration(proxyBeanMethods = false)@ConditionalOnBlockingDiscoveryEnabled@Order(REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER + 1)public static class BlockingSupportConfiguration {@Bean@ConditionalOnBean(DiscoveryClient.class)@ConditionalOnMissingBean@Conditional(DefaultConfigurationCondition.class)public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(ConfigurableApplicationContext context) {return ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withCaching().build(context);}}//省略
}

可以看都是在LoadBalancerClientConfiguration 中配置的，可见此配置类的重要程度

web环境的加载就是BlockingSupportConfiguration下的discoveryClientServiceInstanceListSupplier

@Bean
@ConditionalOnBean(DiscoveryClient.class)
@ConditionalOnMissingBean
@Conditional(DefaultConfigurationCondition.class)
public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(ConfigurableApplicationContext context) {return ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withCaching().build(context);
}

调用了ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withCaching().build(context)来创建ServiceInstanceListSupplier 。这一行有多个方法，我们逐个分析

ServiceInstanceListSupplier

public interface ServiceInstanceListSupplier extends Supplier<Flux<List<ServiceInstance>>> {String getServiceId();default Flux<List<ServiceInstance>> get(Request request) {return get();}static ServiceInstanceListSupplierBuilder builder() {return new ServiceInstanceListSupplierBuilder();}}

提供了builder方法返回 ServiceInstanceListSupplierBuilder 实例

ServiceInstanceListSupplierBuilder

public final class ServiceInstanceListSupplierBuilder {private static final Log LOG = LogFactory.getLog(ServiceInstanceListSupplierBuilder.class);private Creator baseCreator;private DelegateCreator cachingCreator;private final List<DelegateCreator> creators = new ArrayList<>();ServiceInstanceListSupplierBuilder() {}/*** Sets a blocking {@link DiscoveryClient}-based* {@link DiscoveryClientServiceInstanceListSupplier} as a base* {@link ServiceInstanceListSupplier} in the hierarchy.* @return the {@link ServiceInstanceListSupplierBuilder} object*/public ServiceInstanceListSupplierBuilder withBlockingDiscoveryClient() {if (baseCreator != null && LOG.isWarnEnabled()) {LOG.warn("Overriding a previously set baseCreator with a blocking DiscoveryClient baseCreator.");}this.baseCreator = context -> {//获取注册中心的操作对象 discoveryClient DiscoveryClient discoveryClient = context.getBean(DiscoveryClient.class);return new DiscoveryClientServiceInstanceListSupplier(discoveryClient, context.getEnvironment());};return this;}/*** If {@link LoadBalancerCacheManager} is available in the context, wraps created* {@link ServiceInstanceListSupplier} hierarchy with a* {@link CachingServiceInstanceListSupplier} instance to provide a caching mechanism* for service instances. Uses {@link ObjectProvider} to lazily resolve* {@link LoadBalancerCacheManager}.* @return the {@link ServiceInstanceListSupplierBuilder} object*/public ServiceInstanceListSupplierBuilder withCaching() {if (cachingCreator != null && LOG.isWarnEnabled()) {LOG.warn("Overriding a previously set cachingCreator with a CachingServiceInstanceListSupplier-based cachingCreator.");}this.cachingCreator = (context, delegate) -> {ObjectProvider<LoadBalancerCacheManager> cacheManagerProvider = context.getBeanProvider(LoadBalancerCacheManager.class);if (cacheManagerProvider.getIfAvailable() != null) {return new CachingServiceInstanceListSupplier(delegate, cacheManagerProvider.getIfAvailable());}if (LOG.isWarnEnabled()) {LOG.warn("LoadBalancerCacheManager not available, returning delegate without caching.");}return delegate;};return this;}/*** Builds the {@link ServiceInstanceListSupplier} hierarchy.* @param context application context* @return a {@link ServiceInstanceListSupplier} instance on top of the delegate* hierarchy*/public ServiceInstanceListSupplier build(ConfigurableApplicationContext context) {Assert.notNull(baseCreator, "A baseCreator must not be null");ServiceInstanceListSupplier supplier = baseCreator.apply(context);for (DelegateCreator creator : creators) {supplier = creator.apply(context, supplier);}if (this.cachingCreator != null) {supplier = this.cachingCreator.apply(context, supplier);}return supplier;}//省略
}

在调用withBlockingDiscoveryClient()方法，内部调用了new DiscoveryClientServiceInstanceListSupplier(discoveryClient, context.getEnvironment())

DiscoveryClientServiceInstanceListSupplier

public class DiscoveryClientServiceInstanceListSupplier implements ServiceInstanceListSupplier {/*** Property that establishes the timeout for calls to service discovery.*/public static final String SERVICE_DISCOVERY_TIMEOUT = "spring.cloud.loadbalancer.service-discovery.timeout";private static final Log LOG = LogFactory.getLog(DiscoveryClientServiceInstanceListSupplier.class);private Duration timeout = Duration.ofSeconds(30);private final String serviceId;private final Flux<List<ServiceInstance>> serviceInstances;public DiscoveryClientServiceInstanceListSupplier(DiscoveryClient delegate, Environment environment) {this.serviceId = environment.getProperty(PROPERTY_NAME);resolveTimeout(environment);//delegate.getInstances(serviceId)就是从注册中心拉取服务列表了，//然后赋给serviceInstances this.serviceInstances = Flux.defer(() -> Mono.fromCallable(() -> delegate.getInstances(serviceId))).timeout(timeout, Flux.defer(() -> {logTimeout();return Flux.just(new ArrayList<>());}), Schedulers.boundedElastic()).onErrorResume(error -> {logException(error);return Flux.just(new ArrayList<>());});}//省略@Overridepublic String getServiceId() {return serviceId;}@Overridepublic Flux<List<ServiceInstance>> get() {return serviceInstances;}private void resolveTimeout(Environment environment) {String providedTimeout = environment.getProperty(SERVICE_DISCOVERY_TIMEOUT);if (providedTimeout != null) {timeout = DurationStyle.detectAndParse(providedTimeout);}}private void logTimeout() {if (LOG.isDebugEnabled()) {LOG.debug(String.format("Timeout occurred while retrieving instances for service %s."+ "The instances could not be retrieved during %s", serviceId, timeout));}}private void logException(Throwable error) {if (LOG.isErrorEnabled()) {LOG.error(String.format("Exception occurred while retrieving instances for service %s", serviceId), error);}}}

然后就来到了withCaching()

public ServiceInstanceListSupplierBuilder withCaching() {if (cachingCreator != null && LOG.isWarnEnabled()) {LOG.warn("Overriding a previously set cachingCreator with a CachingServiceInstanceListSupplier-based cachingCreator.");}this.cachingCreator = (context, delegate) -> {ObjectProvider<LoadBalancerCacheManager> cacheManagerProvider = context.getBeanProvider(LoadBalancerCacheManager.class);if (cacheManagerProvider.getIfAvailable() != null) {return new CachingServiceInstanceListSupplier(delegate, cacheManagerProvider.getIfAvailable());}if (LOG.isWarnEnabled()) {LOG.warn("LoadBalancerCacheManager not available, returning delegate without caching.");}return delegate;};return this;
}

build(context)进行构建

public ServiceInstanceListSupplier build(ConfigurableApplicationContext context) {Assert.notNull(baseCreator, "A baseCreator must not be null");ServiceInstanceListSupplier supplier = baseCreator.apply(context);for (DelegateCreator creator : creators) {supplier = creator.apply(context, supplier);}if (this.cachingCreator != null) {supplier = this.cachingCreator.apply(context, supplier);}return supplier;
}