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
@ConditionalOnMissingBean
public 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
@Override
public String getServiceId() {
return serviceId;
}
@Override
public 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;
}