spring cloud 2021.x 源码阅读, OpenFeign + LoadBalancer + Nacos Discovery

pom.xml

@@ -62,10 +62,10 @@
 				<groupId>io.spring.javaformat</groupId>
 				<artifactId>spring-javaformat-maven-plugin</artifactId>
 			</plugin>
-			<plugin>
-				<groupId>org.apache.maven.plugins</groupId>
-				<artifactId>maven-checkstyle-plugin</artifactId>
-			</plugin>
+<!--			<plugin>-->
+<!--				<groupId>org.apache.maven.plugins</groupId>-->
+<!--				<artifactId>maven-checkstyle-plugin</artifactId>-->
+<!--			</plugin>-->
 			<plugin>
 				<groupId>org.basepom.maven</groupId>
 				<artifactId>duplicate-finder-maven-plugin</artifactId>
@@ -73,14 +73,14 @@
 		</plugins>
 	</build>
 
-	<reporting>
-		<plugins>
-			<plugin>
-				<groupId>org.apache.maven.plugins</groupId>
-				<artifactId>maven-checkstyle-plugin</artifactId>
-			</plugin>
-		</plugins>
-	</reporting>
+<!--	<reporting>-->
+<!--		<plugins>-->
+<!--			<plugin>-->
+<!--				<groupId>org.apache.maven.plugins</groupId>-->
+<!--				<artifactId>maven-checkstyle-plugin</artifactId>-->
+<!--			</plugin>-->
+<!--		</plugins>-->
+<!--	</reporting>-->
 
 	<profiles>
 		<profile>

spring-cloud-context/src/main/java/org/springframework/cloud/context/named/ClientFactoryObjectProvider.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.context.named;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import java.util.Iterator;
 import java.util.Spliterator;
 import java.util.function.Consumer;
@@ -36,10 +36,13 @@ class ClientFactoryObjectProvider<T> implements ObjectProvider<T> {
 
 	private final NamedContextFactory<?> clientFactory;
 
+	// 服务的名称
 	private final String name;
 
+	// 固定为ServiceInstanceListSupplier
 	private final Class<T> type;
 
+	// 隔离provider，provider只返回clientFactory中指定name,type的数据
 	private ObjectProvider<T> provider;
 
 	ClientFactoryObjectProvider(NamedContextFactory<?> clientFactory, String name, Class<T> type) {

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/annotation/LoadBalancerClientConfiguration.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.loadbalancer.annotation;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import reactor.util.retry.RetrySpec;
 
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
@@ -63,20 +63,28 @@ public class LoadBalancerClientConfiguration {
 
 	private static final int REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER = 193827465;
 
+	// 首先，在前文可以看到在 LoadBalancerAutoConfiguration 配置中，配置了 LoadBalancerClientFactory ，其实例 bean 存在于父容器中，
+	// 而当前配置类 LoadBalancerClientConfiguration 通过构造函数会当成默认配置类注册到 NamedContextFactory 的子容器中，每个子容器都拥有。
+	// 只有明白了这一点，才能够理解容器的隔离。
 	@Bean
-	@ConditionalOnMissingBean
+	@ConditionalOnMissingBean // ConditionalOnMissingBean 说明可以自己实现这个bean，来覆盖默认的配置。
 	public ReactorLoadBalancer<ServiceInstance> reactorServiceInstanceLoadBalancer(Environment environment,
 			LoadBalancerClientFactory loadBalancerClientFactory) {
+		// name表示服务名称，比如stock-service
+		// LoadBalancerClientFactory bean的配置：参考代码 LoadBalancerAutoConfiguration
 		String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);
 		return new RoundRobinLoadBalancer(
 				loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name);
 	}
 
+	// ============================= Reactive Retry ============================= //
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnReactiveDiscoveryEnabled
 	@Order(REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER)
 	public static class ReactiveSupportConfiguration {
 
+		// ReactiveDiscoveryClient + DefaultConfigurationCondition
 		@Bean
 		@ConditionalOnBean(ReactiveDiscoveryClient.class)
 		@ConditionalOnMissingBean
@@ -86,6 +94,7 @@ public class LoadBalancerClientConfiguration {
 			return ServiceInstanceListSupplier.builder().withDiscoveryClient().withCaching().build(context);
 		}
 
+		// ReactiveDiscoveryClient + ZonePreferenceConfigurationCondition
 		@Bean
 		@ConditionalOnBean(ReactiveDiscoveryClient.class)
 		@ConditionalOnMissingBean
@@ -134,11 +143,17 @@ public class LoadBalancerClientConfiguration {
 
 	}
 
+	// ============================= Blocking Retry ============================= //
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnBlockingDiscoveryEnabled
 	@Order(REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER + 1)
 	public static class BlockingSupportConfiguration {
 
+		// 真正获取  ServiceInstance 列表的 由 ServiceInstanceListSupplier 提供，
+		// 这里可以看到可以由 DiscoveryClient 提供。这样就已经跟注册中心客户端联系上了。
+
+		// DiscoveryClient + DefaultConfigurationCondition
 		@Bean
 		@ConditionalOnBean(DiscoveryClient.class)
 		@ConditionalOnMissingBean
@@ -148,6 +163,7 @@ public class LoadBalancerClientConfiguration {
 			return ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withCaching().build(context);
 		}
 
+		// DiscoveryClient + ZonePreferenceConfigurationCondition
 		@Bean
 		@ConditionalOnBean(DiscoveryClient.class)
 		@ConditionalOnMissingBean
@@ -190,6 +206,8 @@ public class LoadBalancerClientConfiguration {
 
 	}
 
+	// ============================= Blocking Retry ============================= //
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnBlockingDiscoveryEnabled
 	@ConditionalOnClass(RetryTemplate.class)
@@ -208,6 +226,8 @@ public class LoadBalancerClientConfiguration {
 
 	}
 
+	// ============================= Reactive Retry ============================= //
+
 	@Configuration(proxyBeanMethods = false)
 	@ConditionalOnReactiveDiscoveryEnabled
 	@Conditional(ReactiveOnAvoidPreviousInstanceAndRetryEnabledCondition.class)
@@ -226,6 +246,7 @@ public class LoadBalancerClientConfiguration {
 
 	}
 
+	// ============================= 条件类 ============================= //
 	static final class BlockingOnAvoidPreviousInstanceAndRetryEnabledCondition extends AllNestedConditions {
 
 		private BlockingOnAvoidPreviousInstanceAndRetryEnabledCondition() {

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/blocking/client/BlockingLoadBalancerClient.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.loadbalancer.blocking.client;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import java.io.IOException;
 import java.net.URI;
 import java.util.Set;
@@ -168,10 +168,14 @@ public class BlockingLoadBalancerClient implements LoadBalancerClient {
 
 	@Override
 	public <T> ServiceInstance choose(String serviceId, Request<T> request) {
+		// ReactiveLoadBalancer 可以是 RoundRobinLoadBalancer，RandomLoadBalancer
+		// loadBalancerClientFactory继承NamedContextFactory，使用子容器实现隔离
 		ReactiveLoadBalancer<ServiceInstance> loadBalancer = loadBalancerClientFactory.getInstance(serviceId);
 		if (loadBalancer == null) {
 			return null;
 		}
+
+		// loadBalancer.choose，返回NacosServiceInstance
 		Response<ServiceInstance> loadBalancerResponse = Mono.from(loadBalancer.choose(request)).block();
 		if (loadBalancerResponse == null) {
 			return null;

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/config/LoadBalancerAutoConfiguration.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.loadbalancer.config;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import java.util.Collections;
 import java.util.List;
 
@@ -48,6 +48,7 @@ public class LoadBalancerAutoConfiguration {
 
 	private final ObjectProvider<List<LoadBalancerClientSpecification>> configurations;
 
+	// 1. Spring 的特性，对于 Configuration ，其构造函数只有一个参数的时候，是可以自动注入的
 	public LoadBalancerAutoConfiguration(ObjectProvider<List<LoadBalancerClientSpecification>> configurations) {
 		this.configurations = configurations;
 	}
@@ -62,6 +63,7 @@ public class LoadBalancerAutoConfiguration {
 	@Bean
 	public LoadBalancerClientFactory loadBalancerClientFactory(LoadBalancerClientsProperties properties) {
 		LoadBalancerClientFactory clientFactory = new LoadBalancerClientFactory(properties);
+		// 【重要】这一步将配置类注入到 NamedContextFactory 中，实现个性化配置。
 		clientFactory.setConfigurations(this.configurations.getIfAvailable(Collections::emptyList));
 		return clientFactory;
 	}

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/core/CachingServiceInstanceListSupplier.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.loadbalancer.core;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import java.util.List;
 
 import org.apache.commons.logging.Log;
@@ -52,21 +52,28 @@ public class CachingServiceInstanceListSupplier extends DelegatingServiceInstanc
 	@SuppressWarnings("unchecked")
 	public CachingServiceInstanceListSupplier(ServiceInstanceListSupplier delegate, CacheManager cacheManager) {
 		super(delegate);
-		this.serviceInstances = CacheFlux.lookup(key -> {
-			// TODO: configurable cache name
-			Cache cache = cacheManager.getCache(SERVICE_INSTANCE_CACHE_NAME);
-			if (cache == null) {
-				if (log.isErrorEnabled()) {
-					log.error("Unable to find cache: " + SERVICE_INSTANCE_CACHE_NAME);
-				}
-				return Mono.empty();
-			}
-			List<ServiceInstance> list = cache.get(key, List.class);
-			if (list == null || list.isEmpty()) {
-				return Mono.empty();
-			}
-			return Flux.just(list).materialize().collectList();
-		}, delegate.getServiceId()).onCacheMissResume(delegate.get().take(1))
+		// lookup的第一个入参：
+		this.serviceInstances = CacheFlux
+				.lookup(key -> {
+							// TODO: configurable cache name
+							Cache cache = cacheManager.getCache(SERVICE_INSTANCE_CACHE_NAME);
+							if (cache == null) {
+								if (log.isErrorEnabled()) {
+									log.error("Unable to find cache: " + SERVICE_INSTANCE_CACHE_NAME);
+								}
+								return Mono.empty();
+							}
+							List<ServiceInstance> list = cache.get(key, List.class);
+							if (list == null || list.isEmpty()) {
+								return Mono.empty();
+							}
+							return Flux.just(list).materialize().collectList();
+						}, delegate.getServiceId()
+				)
+				// 【重要】cache miss时，获取原始数据。
+				// delegate 可以是 DiscoveryClientServiceInstanceListSupplier
+				.onCacheMissResume(delegate.get().take(1))
+				// 同时写入缓存
 				.andWriteWith((key, signals) -> Flux.fromIterable(signals).dematerialize().doOnNext(instances -> {
 					Cache cache = cacheManager.getCache(SERVICE_INSTANCE_CACHE_NAME);
 					if (cache == null) {

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/core/DiscoveryClientServiceInstanceListSupplier.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.loadbalancer.core;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.List;
@@ -74,14 +74,18 @@ public class DiscoveryClientServiceInstanceListSupplier implements ServiceInstan
 	public DiscoveryClientServiceInstanceListSupplier(ReactiveDiscoveryClient delegate, Environment environment) {
 		this.serviceId = environment.getProperty(PROPERTY_NAME);
 		resolveTimeout(environment);
-		this.serviceInstances = Flux
-				.defer(() -> delegate.getInstances(serviceId).collectList().flux().timeout(timeout, Flux.defer(() -> {
-					logTimeout();
-					return Flux.just(new ArrayList<>());
-				})).onErrorResume(error -> {
-					logException(error);
-					return Flux.just(new ArrayList<>());
-				}));
+		this.serviceInstances = Flux.defer(
+				() -> delegate.getInstances(serviceId).collectList()
+						.flux()
+						.timeout(timeout, Flux.defer(() -> {
+							logTimeout();
+							return Flux.just(new ArrayList<>());
+						}))
+						.onErrorResume(error -> {
+							logException(error);
+							return Flux.just(new ArrayList<>());
+						})
+		);
 	}
 
 	@Override

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/core/RoundRobinLoadBalancer.java

@@ -13,9 +13,8 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
 package org.springframework.cloud.loadbalancer.core;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import java.util.List;
 import java.util.Random;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -46,6 +45,11 @@ public class RoundRobinLoadBalancer implements ReactorServiceInstanceLoadBalance
 
 	final String serviceId;
 
+	/**
+	 * 从LoadBalancerClientFactory中获取ServiceInstanceListSupplier类型的 bean
+	 * 实际类型 ClientFactoryObjectProvider 是 getLazyProvider 内的封装类
+	 * @see org.springframework.cloud.loadbalancer.support.LoadBalancerClientFactory
+	 */
 	ObjectProvider<ServiceInstanceListSupplier> serviceInstanceListSupplierProvider;
 
 	/**
@@ -77,21 +81,33 @@ public class RoundRobinLoadBalancer implements ReactorServiceInstanceLoadBalance
 	// https://github.com/Netflix/ocelli/blob/master/ocelli-core/
 	// src/main/java/netflix/ocelli/loadbalancer/RoundRobinLoadBalancer.java
 	public Mono<Response<ServiceInstance>> choose(Request request) {
+		// 获取supplier，调用get方法获取List<ServiceInstance>
+		// 可以是 CachingServiceInstanceListSupplier 类型
+		// 也可以是自定义的ServiceInstanceListSupplier，这取决于调用的上下文。
 		ServiceInstanceListSupplier supplier = serviceInstanceListSupplierProvider
+				// 相当于getOrDefault，实际返回 CachingServiceInstanceListSupplier
 				.getIfAvailable(NoopServiceInstanceListSupplier::new);
-		return supplier.get(request).next()
+		return supplier
+				// get的含义
+				.get(request)
+				// next方法：Flux转化为Mono
+				.next()
+				//
 				.map(serviceInstances -> processInstanceResponse(supplier, serviceInstances));
 	}
 
 	private Response<ServiceInstance> processInstanceResponse(ServiceInstanceListSupplier supplier,
 			List<ServiceInstance> serviceInstances) {
+		// 选择ServiceInstance
 		Response<ServiceInstance> serviceInstanceResponse = getInstanceResponse(serviceInstances);
+		// 回调supplier，告知最终结果
 		if (supplier instanceof SelectedInstanceCallback && serviceInstanceResponse.hasServer()) {
 			((SelectedInstanceCallback) supplier).selectedServiceInstance(serviceInstanceResponse.getServer());
 		}
 		return serviceInstanceResponse;
 	}
 
+	// 轮询算法：在多个instances中选择一个
 	private Response<ServiceInstance> getInstanceResponse(List<ServiceInstance> instances) {
 		if (instances.isEmpty()) {
 			if (log.isWarnEnabled()) {
@@ -100,6 +116,7 @@ public class RoundRobinLoadBalancer implements ReactorServiceInstanceLoadBalance
 			return new EmptyResponse();
 		}
 
+
 		// Ignore the sign bit, this allows pos to loop sequentially from 0 to
 		// Integer.MAX_VALUE
 		int pos = this.position.incrementAndGet() & Integer.MAX_VALUE;

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/core/ServiceInstanceListSupplierBuilder.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.loadbalancer.core;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import java.net.URI;
 import java.util.ArrayList;
 import java.util.List;
@@ -55,6 +55,7 @@ public final class ServiceInstanceListSupplierBuilder {
 
 	private static final Log LOG = LogFactory.getLog(ServiceInstanceListSupplierBuilder.class);
 
+	// DiscoveryClientServiceInstanceListSupplier, 分为Blocking, Reactive两种.
 	private Creator baseCreator;
 
 	private DelegateCreator cachingCreator;
@@ -75,6 +76,7 @@ public final class ServiceInstanceListSupplierBuilder {
 			LOG.warn("Overriding a previously set baseCreator with a blocking DiscoveryClient baseCreator.");
 		}
 		this.baseCreator = context -> {
+			// 构造Blocking DiscoveryClient
 			DiscoveryClient discoveryClient = context.getBean(DiscoveryClient.class);
 
 			return new DiscoveryClientServiceInstanceListSupplier(discoveryClient, context.getEnvironment());
@@ -93,6 +95,9 @@ public final class ServiceInstanceListSupplierBuilder {
 			LOG.warn("Overriding a previously set baseCreator with a ReactiveDiscoveryClient baseCreator.");
 		}
 		this.baseCreator = context -> {
+			// 构造Reactive DiscoveryClient
+			// 可以是ReactiveCompositeDiscoveryClient, 包含一个 NacosReactiveDiscoveryClient + SimpleReactiveDiscoveryClient
+			// 【重要】这里Nacos完成和LoadBalancer的集成
 			ReactiveDiscoveryClient discoveryClient = context.getBean(ReactiveDiscoveryClient.class);
 
 			return new DiscoveryClientServiceInstanceListSupplier(discoveryClient, context.getEnvironment());
@@ -225,6 +230,7 @@ public final class ServiceInstanceListSupplierBuilder {
 			LOG.warn(
 					"Overriding a previously set cachingCreator with a CachingServiceInstanceListSupplier-based cachingCreator.");
 		}
+		// 启用Cache机制，使用CachingServiceInstanceListSupplier包装原始的ServiceInstanceListSupplier
 		this.cachingCreator = (context, delegate) -> {
 			ObjectProvider<LoadBalancerCacheManager> cacheManagerProvider = context
 					.getBeanProvider(LoadBalancerCacheManager.class);
@@ -276,6 +282,7 @@ public final class ServiceInstanceListSupplierBuilder {
 	public ServiceInstanceListSupplier build(ConfigurableApplicationContext context) {
 		Assert.notNull(baseCreator, "A baseCreator must not be null");
 
+		// TODO context为什么是stock-service隔离的 ？
 		ServiceInstanceListSupplier supplier = baseCreator.apply(context);
 
 		for (DelegateCreator creator : creators) {

spring-cloud-loadbalancer/src/main/java/org/springframework/cloud/loadbalancer/support/LoadBalancerClientFactory.java

@@ -15,7 +15,7 @@
  */
 
 package org.springframework.cloud.loadbalancer.support;
-
+// comment-by-kai 源码阅读 spring cloud 2021.x
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
@@ -64,7 +64,10 @@ public class LoadBalancerClientFactory extends NamedContextFactory<LoadBalancerC
 		this(null);
 	}
 
+	// 构造器调用：org.springframework.cloud.client.loadbalancer.LoadBalancerAutoConfiguration
 	public LoadBalancerClientFactory(LoadBalancerClientsProperties properties) {
+		// 这里注意看 LoadBalancerClientConfiguration 被当成了默认配置类注入到 NamedContextFactory 中。也就是说每个子容器都会有这个配置类。
+		// 根据构造器 NamedContextFactory 会构造一个 PropertySource，key=loadbalancer.client.name，value = ？
 		super(LoadBalancerClientConfiguration.class, NAMESPACE, PROPERTY_NAME);
 		this.properties = properties;
 	}