@LoadBalancerClients

终于分析到了此注解的作用，它是实现不同服务之间的配置隔离的关键

@Configuration(proxyBeanMethods = false)
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.TYPE })
@Documented
@Import(LoadBalancerClientConfigurationRegistrar.class)
public @interface LoadBalancerClients {LoadBalancerClient[] value() default {};/*** {@link LoadBalancerClientConfigurationRegistrar} creates a* {@link LoadBalancerClientSpecification} with this as an argument. These in turn are* added as default contexts in {@link LoadBalancerClientFactory}. Configuration* defined in these classes are used as defaults if values aren't defined via* {@link LoadBalancerClient#configuration()}* @return classes for default configurations*/Class<?>[] defaultConfiguration() default {};}@Configuration(proxyBeanMethods = false)
@Import(LoadBalancerClientConfigurationRegistrar.class)
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface LoadBalancerClient {/*** Synonym for name (the name of the client).** @see #name()* @return the name of the load balancer client*/@AliasFor("name")String value() default "";/*** The name of the load balancer client, uniquely identifying a set of client* resources, including a load balancer.* @return the name of the load balancer client*/@AliasFor("value")String name() default "";/*** A custom <code>@Configuration</code> for the load balancer client. Can contain* override <code>@Bean</code> definition for the pieces that make up the client.** @see LoadBalancerClientConfiguration for the defaults* @return configuration classes for the load balancer client.*/Class<?>[] configuration() default {};}

• LoadBalancerClients 就是其实就是多个LoadBalancerClient
• LoadBalancerClient 相当于一个负载均衡配置，name/value 就是 serviceId，configuration 就是负载均衡配置
• 通过@Import(LoadBalancerClientConfigurationRegistrar.class)来进行注入

LoadBalancerClientConfigurationRegistrar

public class LoadBalancerClientConfigurationRegistrar implements ImportBeanDefinitionRegistrar {private static String getClientName(Map<String, Object> client) {if (client == null) {return null;}String value = (String) client.get("value");if (!StringUtils.hasText(value)) {value = (String) client.get("name");}if (StringUtils.hasText(value)) {return value;}throw new IllegalStateException("Either 'name' or 'value' must be provided in @LoadBalancerClient");}private static void registerClientConfiguration(BeanDefinitionRegistry registry, Object name,Object configuration) {BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(LoadBalancerClientSpecification.class);builder.addConstructorArgValue(name);builder.addConstructorArgValue(configuration);//每个LoadBalancerClient其实就是LoadBalancerClientSpecificationregistry.registerBeanDefinition(name + ".LoadBalancerClientSpecification", builder.getBeanDefinition());}@Overridepublic void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {Map<String, Object> attrs = metadata.getAnnotationAttributes(LoadBalancerClients.class.getName(), true);//获取LoadBalancerClients 注解的属性if (attrs != null && attrs.containsKey("value")) {//value属性为LoadBalancerClient注解，可以给configuration赋值，填写需要的配置类，比如RandomLoadBalancerConfig.classAnnotationAttributes[] clients = (AnnotationAttributes[]) attrs.get("value");for (AnnotationAttributes client : clients) {//将配置类 注册到当前容器registerClientConfiguration(registry, getClientName(client), client.get("configuration"));}}if (attrs != null && attrs.containsKey("defaultConfiguration")) {String name;if (metadata.hasEnclosingClass()) {name = "default." + metadata.getEnclosingClassName();}else {name = "default." + metadata.getClassName();}//如果defaultConfiguration有配置，当做默认配置注册中，并赋值给所有容器registerClientConfiguration(registry, name, attrs.get("defaultConfiguration"));}//处理@LoadBalancerClient注解，逻辑和上面LoadBalancerClients的相同Map<String, Object> client = metadata.getAnnotationAttributes(LoadBalancerClient.class.getName(), true);String name = getClientName(client);if (name != null) {//configuration 属性的类 注册到容器中registerClientConfiguration(registry, name, client.get("configuration"));}}}

• LoadBalancerClients有一个默认的配置属性 Class<?>[] configuration() default {};这个属性的类以default. 开头来命名
• LoadBalancerClients含有多个LoadBalancerClient，属性value是serviceId 。属性 Class<?>[] configuration() default {};是当前serviceId名字下的配置
• LoadBalancerClients和每个LoadBalancerClient的configuration都会被封装以clientName为维度的LoadBalancerClientSpecification，注册到当前容器中
• 注意！ 这时注册的是BeanDefinition类型的元数据，还没有开始真正的实例化bean！真正的实例化是在子容器创建的时候会将父容器添加进去，也相当于子容器也含有了，然后会启动子容器这时，就会进行真正的实例化。
• 最终注入到LoadBalancerAutoConfiguration配置类的属性configurations，用于LoadBalancerClientFactory 的实例化
• 当LoadBalancerClientFactory实例化的时候，就会获取LoadBalancerClientSpecification的对象了
  
  可以看到将LoadBalancerAutoConfiguration和BlockingLoadBalancerClientAutoConfiguration注入，包装成LoadBalancerClientSpecification类型

LoadBalancerClientFactory

再看一眼LoadBalancerClientFactorybean实例生成的过程

可以看到将LoadBalancerClientSpecification类型的LoadBalancerAutoConfiguration和BlockingLoadBalancerClientAutoConfiguration通过setConfiguations方法注入了进入

setConfiguations方法是在父类NamedContextFactory中执行的，稍微会分析NamedContextFactory，这里先分析LoadBalancerClientFactory 的结构

public class LoadBalancerClientFactory extends NamedContextFactory<LoadBalancerClientSpecification>implements ReactiveLoadBalancer.Factory<ServiceInstance> {private static final Log log = LogFactory.getLog(LoadBalancerClientFactory.class);/*** Property source name for load balancer.*/public static final String NAMESPACE = "loadbalancer";/*** Property for client name within the load balancer namespace.*/public static final String PROPERTY_NAME = NAMESPACE + ".client.name";private final LoadBalancerClientsProperties properties;public LoadBalancerClientFactory(LoadBalancerClientsProperties properties) {//记住这个LoadBalancerClientConfiguration，被当成了默认配置类注入到 NamedContextFactory ，也就是每个子容器都会有这个配置类super(LoadBalancerClientConfiguration.class, NAMESPACE, PROPERTY_NAME);this.properties = properties;}public static String getName(Environment environment) {return environment.getProperty(PROPERTY_NAME);}@Overridepublic ReactiveLoadBalancer<ServiceInstance> getInstance(String serviceId) {return getInstance(serviceId, ReactorServiceInstanceLoadBalancer.class);}@Overridepublic LoadBalancerProperties getProperties(String serviceId) {if (properties == null) {if (log.isWarnEnabled()) {log.warn("LoadBalancerClientsProperties is null. Please use the new constructor.");}return null;}if (serviceId == null || !properties.getClients().containsKey(serviceId)) {// no specific client properties, return defaultreturn properties;}// because specifics are overlayed on top of defaults, everything in `properties`,// unless overridden, is in `clientsProperties`return properties.getClients().get(serviceId);}}

既然LoadBalancerClientConfiguration注入到NamedContextFactory中，我们就分析此配置类

LoadBalancerClientConfiguration

@Configuration(proxyBeanMethods = false)
@ConditionalOnDiscoveryEnabled
public class LoadBalancerClientConfiguration {private static final int REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER = 193827465;/*** 怕读者忘了此配置的注入过程，这里再说一下* 上文说的LoadBalancerAutoConfiguration配置类中，创建了 LoadBalancerClientFactory 的bean对象，存在于父容器中* 在此bean创建的过程中，会通过构造方法将此配置LoadBalancerClientConfiguration转入到LoadBalancerClientFactory中* 然后会当做默认配置类注册到 NamedContextFactory 的子容器中，这样每个子容器都拥有* 我们也可以自己实现这个ReactorLoadBalancer类型的bean，覆盖此配置** */@Bean@ConditionalOnMissingBeanpublic ReactorLoadBalancer<ServiceInstance> reactorServiceInstanceLoadBalancer(Environment environment,LoadBalancerClientFactory loadBalancerClientFactory) {// 获取当前子容器的名称（也是服务名）String name = environment.getProperty(LoadBalancerClientFactory.PROPERTY_NAME);return new RoundRobinLoadBalancer(loadBalancerClientFactory.getLazyProvider(name, ServiceInstanceListSupplier.class), name);}//省略...@Configuration(proxyBeanMethods = false)@ConditionalOnBlockingDiscoveryEnabled@Order(REACTIVE_SERVICE_INSTANCE_SUPPLIER_ORDER + 1)public static class BlockingSupportConfiguration {//ServiceInstanceListSupplier来查询ServiceInstance服务列表，能看到这里是DiscoveryClient提供的。这样就和注册中心关联了@Bean@ConditionalOnBean(DiscoveryClient.class)@ConditionalOnMissingBean@Conditional(DefaultConfigurationCondition.class)public ServiceInstanceListSupplier discoveryClientServiceInstanceListSupplier(ConfigurableApplicationContext context) {return ServiceInstanceListSupplier.builder().withBlockingDiscoveryClient().withCaching().build(context);}}//省略...}

LoadBalancerClientConfiguration的作用分析完了，在上文中

public LoadBalancerClientFactory(LoadBalancerClientsProperties properties) {//记住这个LoadBalancerClientConfiguration，被当成了默认配置类注入到 NamedContextFactory ，也就是每个子容器都会有这个配置类super(LoadBalancerClientConfiguration.class, NAMESPACE, PROPERTY_NAME);this.properties = properties;
}

LoadBalancerClientConfiguration是传给了父类，LoadBalancerClientFactory 的结构

public class LoadBalancerClientFactory extends NamedContextFactory<LoadBalancerClientSpecification>implements ReactiveLoadBalancer.Factory<ServiceInstance> {..}

在LoadBalancerClientFactory生成bean的过程中，调用完构造方法后，又执行了clientFactory.setConfigurations(this.configurations.getIfAvailable(Collections::emptyList))，此方法是在父类NamedContextFactory执行的

看一下clientFactory.setConfigurations(this.configurations.getIfAvailable(Collections::emptyList))执行结果

下面我们要分析父类NamedContextFactory，非常的重要

NamedContextFactory

public abstract class NamedContextFactory<C extends NamedContextFactory.Specification>implements DisposableBean, ApplicationContextAware {private final String propertySourceName;private final String propertyName;private Map<String, AnnotationConfigApplicationContext> contexts = new ConcurrentHashMap<>();private Map<String, C> configurations = new ConcurrentHashMap<>();private ApplicationContext parent;private Class<?> defaultConfigType;/*** defaultConfigType是刚才文中说的子类LoadBalancerClientFactory创建时注入的。类型为LoadBalancerClientConfiguration* */public NamedContextFactory(Class<?> defaultConfigType, String propertySourceName, String propertyName) {this.defaultConfigType = defaultConfigType;this.propertySourceName = propertySourceName;this.propertyName = propertyName;}@Overridepublic void setApplicationContext(ApplicationContext parent) throws BeansException {this.parent = parent;}public ApplicationContext getParent() {return parent;}/*** configurations为LoadBalancerAutoConfiguration和BlockingLoadBalancerClientAutoConfiguration，* 文中刚才分析过* */public void setConfigurations(List<C> configurations) {for (C client : configurations) {this.configurations.put(client.getName(), client);}}public Set<String> getContextNames() {return new HashSet<>(this.contexts.keySet());}@Overridepublic void destroy() {Collection<AnnotationConfigApplicationContext> values = this.contexts.values();for (AnnotationConfigApplicationContext context : values) {// This can fail, but it never throws an exception (you see stack traces// logged as WARN).context.close();}this.contexts.clear();}protected AnnotationConfigApplicationContext getContext(String name) {if (!this.contexts.containsKey(name)) {synchronized (this.contexts) {if (!this.contexts.containsKey(name)) {//如果不存在则先创建容器this.contexts.put(name, createContext(name));}}}return this.contexts.get(name);}protected AnnotationConfigApplicationContext createContext(String name) {AnnotationConfigApplicationContext context;//创建容器if (this.parent != null) {DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();if (parent instanceof ConfigurableApplicationContext) {beanFactory.setBeanClassLoader(((ConfigurableApplicationContext) parent).getBeanFactory().getBeanClassLoader());}else {beanFactory.setBeanClassLoader(parent.getClassLoader());}context = new AnnotationConfigApplicationContext(beanFactory);context.setClassLoader(this.parent.getClassLoader());}else {context = new AnnotationConfigApplicationContext();}//configurations就是LoadBalancerClientSpecification类型的LoadBalancerAutoConfiguration和BlockingLoadBalancerClientAutoConfiguration//这里是将@LoadBalancerClient对应的负载均衡配置注册到对应的容器中//由以上可知通过此步我们可以使用@LoadBalancerClient自定义负载均衡策略//如果不自定义的话，这里为falseif (this.configurations.containsKey(name)) {for (Class<?> configuration : this.configurations.get(name).getConfiguration()) {context.register(configuration);}}//也就是将configurations中LoadBalancerClientSpecification类型的LoadBalancerAutoConfiguration和BlockingLoadBalancerClientAutoConfiguration注册到容器中//这样每个容器就拥有了for (Map.Entry<String, C> entry : this.configurations.entrySet()) {if (entry.getKey().startsWith("default.")) {for (Class<?> configuration : entry.getValue().getConfiguration()) {context.register(configuration);}}}//defaultConfigType就是LoadBalancerClientConfiguration，在子类LoadBalancerClientFactory的构造方法传入//在刚才分析LoadBalancerClientFactory的时候介绍过context.register(PropertyPlaceholderAutoConfiguration.class, this.defaultConfigType);context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(this.propertySourceName,Collections.<String, Object>singletonMap(this.propertyName, name)));//将父容器添加进去if (this.parent != null) {// Uses Environment from parent as well as beanscontext.setParent(this.parent);}context.setDisplayName(generateDisplayName(name));context.refresh();return context;}protected String generateDisplayName(String name) {return this.getClass().getSimpleName() + "-" + name;}/*** 每个LoadBalancerClientSpecification都创建一个AnnotationConfigApplicationContext* 也就是每个LoadBalancerClient会对应一个容器，其中的配置就对应容器中bean实例* */public <T> T getInstance(String name, Class<T> type) {//获取AnnotationConfigApplicationContext类型的容器AnnotationConfigApplicationContext context = getContext(name);try {//从容器中获取对应的实例return context.getBean(type);}catch (NoSuchBeanDefinitionException e) {// ignore}return null;}public <T> ObjectProvider<T> getLazyProvider(String name, Class<T> type) {return new ClientFactoryObjectProvider<>(this, name, type);}public <T> ObjectProvider<T> getProvider(String name, Class<T> type) {AnnotationConfigApplicationContext context = getContext(name);return context.getBeanProvider(type);}public <T> T getInstance(String name, Class<?> clazz, Class<?>... generics) {ResolvableType type = ResolvableType.forClassWithGenerics(clazz, generics);return getInstance(name, type);}@SuppressWarnings("unchecked")public <T> T getInstance(String name, ResolvableType type) {AnnotationConfigApplicationContext context = getContext(name);String[] beanNames = BeanFactoryUtils.beanNamesForTypeIncludingAncestors(context, type);if (beanNames.length > 0) {for (String beanName : beanNames) {if (context.isTypeMatch(beanName, type)) {return (T) context.getBean(beanName);}}}return null;}public <T> Map<String, T> getInstances(String name, Class<T> type) {AnnotationConfigApplicationContext context = getContext(name);return BeanFactoryUtils.beansOfTypeIncludingAncestors(context, type);}/*** Specification with name and configuration.*/public interface Specification {String getName();Class<?>[] getConfiguration();}}

到这里将每个@LoadBalancerClient都创建了AnnotationConfigApplicationContext的容器，然后放到了 LoadBalancerClientFactory中

到这里bean的生成过程分析完毕，下一篇文章会分析整个执行过程