Spring - 揭秘Ribbon配置类为什么不能在主应用程序上下文的@ComponentScan中 - 《开发笔记》

揭秘Ribbon配置类为什么不能在主应用程序上下文的@ComponentScan中
补充

揭秘Ribbon配置类为什么不能在主应用程序上下文的@ComponentScan中

SpringCloud 的中文分享还是比较少的，例如在自定义Ribbon配置中，网上很多文章都会说明 Ribbon配置类不能在主应用程序上下文的@ComponentScan中 , 否则就会被声明为 共享 , 但是为什么呢? 却少有人谈. 本文结合实际代码揭秘.

写之前先抛出如下问题

一个web应用可以用过多少个 Spring Context(Spring上下文环境)

前情提要

1、写过 SpringBoot 应用的同学都知道，SpringBoot 会自动加载自己包及其子包下边的 class, 如果有其他的 Bean 不在这个里边，那么就需要通过 @Configuration 或者增加 @ComponentScan 的扫描区域.

2、在通常的web应用中，会存在2个 Spring Context ，分别是

org.springframework.web.servlet.FrameworkServlet.CONTEXT web子容器.
WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE ROOT , parent 容器.

在这个基础上，可以针对他们进行拓展，每一个 key 单独拓展一个 Spring Context ，参考 ==> AnnotationConfigApplicationContext

揭秘

前一阵弄 注册中心时 需要单独实现一些配置去操作 Ribbon 的配置时，必然会出现 No qualifying bean of type ‘com.netflix.client.config.IClientConfig’ available . 经过深入了解发现如下结论.

每一个 ServiceId 都有她专属的 Spring Context .

这样就可以解释为什么在 XxxxxxRibbonClientConfiguration 获取不到 com.netflix.client.config.IClientConfig. 同时也正是因为这个是 子容器 通过 AnnotationConfigApplicationContext 进行读取的，如果将 配置放置到到主应用程序上下文的@ComponentScan中，则会被主应用的上下文读取，最终被所有的 上下文共享 .

代码配置如下: 分别是

通过 org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.netflix.loadbalancer.RaycloudNacosAutoConfiguration 引入配置文件，使用注解的形式进行我失败了.
加载自定义的配置.

@Configuration
@EnableConfigurationProperties
@ConditionalOnBean({SpringClientFactory.class})
@ConditionalOnRibbonNacos
@ConditionalOnNacosDiscoveryEnabled
@AutoConfigureAfter({RibbonAutoConfiguration.class})
@RibbonClients(
        defaultConfiguration = {RaycloudRibbonClientConfiguration.class}
)
public class RaycloudNacosAutoConfiguration {
}

config:

@Configuration
public class RaycloudRibbonClientConfiguration {
    @Bean
    @LoadBalanced
    public RestTemplate getRestTemplate() {
        return new RestTemplate();
    }
    @Bean
    public IRule rule(IClientConfig config) {
        RaycloudRule raycloudRule = new RaycloudRule();
        raycloudRule.initWithNiwsConfig(config);
        return raycloudRule;
    }
    @Bean
    @ConditionalOnMissingBean
    public ServerListUpdater ribbonServerListUpdater(IClientConfig config) {
        return new MyPoolUpdater(config);
    }
    /**
     * {@link RibbonClientConfiguration#ribbonLoadBalancer(IClientConfig, ServerList, ServerListFilter, IRule, IPing, ServerListUpdater)}  )}
     */
    @Bean
    @ConditionalOnMissingBean
    public ILoadBalancer ribbonLoadBalancer(IClientConfig config, ServerList serverList, ServerListFilter serverListFilter, IRule rule, IPing ping, ServerListUpdater serverListUpdater) {
        if (this.propertiesFactory.isSet(ILoadBalancer.class, "client")) {
            return this.propertiesFactory.get(ILoadBalancer.class, config, "client");
        }
        return new MyLoad(config, rule, ping, serverList, serverListFilter, serverListUpdater);
    }
    @Autowired
    private PropertiesFactory propertiesFactory;
}

没有服务实例时销毁服务的Spring上下文

public class MyPoolUpdater extends PollingServerListUpdater {
    public MyPoolUpdater(IClientConfig clientConfig) {
        super(init(clientConfig));
    }
    public static IClientConfig config = null;
    @Autowired
    private SpringClientFactory springClientFactory;
    private static IClientConfig init(IClientConfig clientConfig) {
        config = clientConfig;
        return clientConfig;
    }
    public MyPoolUpdater(long initialDelayMs, long refreshIntervalMs) {
        super(initialDelayMs, refreshIntervalMs);
    }
    private UpdateAction updateAction;
    @Override
    public synchronized void start(final UpdateAction updateAction) {
        super.start(updateAction);
        this.updateAction = updateAction;
    }
    @Override
    public synchronized void stop() {
        super.stop();
        if (springClientFactory != null) {
            try {
                Field contexts = springClientFactory.getClass().getSuperclass().getDeclaredField("contexts");
                contexts.setAccessible(true);
                Map<String, AnnotationConfigApplicationContext> contextMap = (Map<String, AnnotationConfigApplicationContext>) contexts.get(springClientFactory);
                AnnotationConfigApplicationContext annotationConfigApplicationContext = contextMap.remove(config.getClientName());
                if (annotationConfigApplicationContext != null) {
                    annotationConfigApplicationContext.close();
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }
    public UpdateAction getUpdateAction() {
        return updateAction;
    }
}

SpringClientFactory.

A factory that creates client, load balancer and client configuration instances. It creates a Spring ApplicationContext per client name, and extracts the beans that it needs from there.

创建 Context 的类，English就不解释了.

为 ServiceId 单独创建上下文

protected AnnotationConfigApplicationContext createContext(String name) {
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
    if (this.configurations.containsKey(name)) {
        for (Class<?> configuration : this.configurations.get(name)
                .getConfiguration()) {
            context.register(configuration);
        }
    }
    for (Map.Entry<String, C> entry : this.configurations.entrySet()) {
        if (entry.getKey().startsWith("default.")) {
            for (Class<?> configuration : entry.getValue().getConfiguration()) {
                context.register(configuration);
            }
        }
    }
    context.register(PropertyPlaceholderAutoConfiguration.class,
            this.defaultConfigType);
    context.getEnvironment().getPropertySources().addFirst(new MapPropertySource(
            this.propertySourceName,
            Collections.<String, Object> singletonMap(this.propertyName, name)));
    if (this.parent != null) {
        // Uses Environment from parent as well as beans
        context.setParent(this.parent);
    }
    context.setDisplayName(generateDisplayName(name));
    context.refresh();
    return context;
}

过程也不解释了，这里反向列一下源代码的过程. (查阅时记得从下往上)

RibbonAutoConfiguration#springClientFactory
RibbonClientConfigurationRegistrar#registerBeanDefinitions
RibbonClients

看完这部分就可以了解为为什么是通过 @RibbonClient 和 @RibbonClients 进入导入了.

补充

public class TestMoreContext {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
        context.register(Hello.class);
        context.refresh();
        Object bean = context.getBean("good");
        System.out.println("bean:" + bean);
        AnnotationConfigApplicationContext lastContext = new AnnotationConfigApplicationContext();
        lastContext.register(CC.class);
        lastContext.setParent(context);
        lastContext.refresh();
        Date date = lastContext.getBean("last", Date.class);
        System.out.println(date);
        String good = context.getBean("good", String.class);
        System.out.println("good:" + good);
    }
}

2019-09-01