nacos动态刷新配置原理

Nacos动态配置刷新

环境

springboot	3.0.5
springCloud	2022.0.3
springCloudAlibaba	2022.0.0.0-RC2

探索

共有两种方式来获取nacos的配置

1. @ConfigurationProperties

2. @Value+@RefreshScope

配置类形式

原理：通过监听nacos端的配置动态变化

使用springboot的事件监听机制

监听器如下

	@Override
	public void onApplicationEvent(ApplicationEvent event) {
		if (event instanceof ApplicationReadyEvent) {
			handle((ApplicationReadyEvent) event);
		}
		else if (event instanceof RefreshEvent) {
          // 刷新事件
			handle((RefreshEvent) event);
		}
	}

public void handle(RefreshEvent event) {
		if (this.ready.get()) { // don't handle events before app is ready
			log.debug("Event received " + event.getEventDesc());
          // 进行刷新
			Set<String> keys = this.refresh.refresh();
			log.info("Refresh keys changed: " + keys);
		}
	}

跳转到ContextRefresher类中

public synchronized Set<String> refreshEnvironment() {
		// 获取之前的配置
  Map<String, Object> before = extract(this.context.getEnvironment().getPropertySources());
		// 加载配置文件到ioc容器中？
  updateEnvironment();
		Set<String> keys = changes(before, extract(this.context.getEnvironment().getPropertySources())).keySet();
		this.context.publishEvent(new EnvironmentChangeEvent(this.context, keys));
		return keys;
	}

下面是更新配置的代码

@Override
protected void updateEnvironment() {
    addConfigFilesToEnvironment();
}

/* For testing. */ ConfigurableApplicationContext addConfigFilesToEnvironment() {
    ConfigurableApplicationContext capture = null;
    try {
      // 当前的
       StandardEnvironment environment = copyEnvironment(getContext().getEnvironment());

       Map<String, Object> map = new HashMap<>();
       map.put("spring.jmx.enabled", false);
       map.put("spring.main.sources", "");
       // gh-678 without this apps with this property set to REACTIVE or SERVLET fail
       map.put("spring.main.web-application-type", "NONE");
       map.put(BOOTSTRAP_ENABLED_PROPERTY, Boolean.TRUE.toString());
       environment.getPropertySources().addFirst(new MapPropertySource(REFRESH_ARGS_PROPERTY_SOURCE, map));
// 又创造了一个ioc容器???
       SpringApplicationBuilder builder = new SpringApplicationBuilder(Empty.class).bannerMode(Banner.Mode.OFF)
             .web(WebApplicationType.NONE).environment(environment);
       // Just the listeners that affect the environment (e.g. excluding logging
       // listener because it has side effects)
       builder.application().setListeners(
             Arrays.asList(new BootstrapApplicationListener(), new BootstrapConfigFileApplicationListener()));
       capture = builder.run();
       if (environment.getPropertySources().contains(REFRESH_ARGS_PROPERTY_SOURCE)) {
          environment.getPropertySources().remove(REFRESH_ARGS_PROPERTY_SOURCE);
       }
       MutablePropertySources target = getContext().getEnvironment().getPropertySources();
       String targetName = null;
       for (PropertySource<?> source : environment.getPropertySources()) {
          String name = source.getName();
          if (target.contains(name)) {
             targetName = name;
          }
          if (!this.standardSources.contains(name)) {
             if (target.contains(name)) {
               // 看不懂 应该是替换文件
                target.replace(name, source);
             }
             else {
                if (targetName != null) {
                   target.addAfter(targetName, source);
                   // update targetName to preserve ordering
                   targetName = name;
                }
                else {
                   // targetName was null so we are at the start of the list
                   target.addFirst(source);
                   targetName = name;
                }
             }
          }
       }
    }
    finally {
       ConfigurableApplicationContext closeable = capture;
       while (closeable != null) {
          try {
             closeable.close();
          }
          catch (Exception e) {
             // Ignore;
          }
          if (closeable.getParent() instanceof ConfigurableApplicationContext) {
             closeable = (ConfigurableApplicationContext) closeable.getParent();
          }
          else {
             break;
          }
       }
    }
    return capture;
}

更新配置

private boolean rebind(String name, ApplicationContext appContext) {
    try {
       Object bean = appContext.getBean(name);
       if (AopUtils.isAopProxy(bean)) {
          bean = ProxyUtils.getTargetObject(bean);
       }
       if (bean != null) {
          // TODO: determine a more general approach to fix this.
          // see
          // https://github.com/spring-cloud/spring-cloud-commons/issues/571
          if (getNeverRefreshable().contains(bean.getClass().getName())) {
             return false; // ignore
          }
         // 下面是核心代码 直接把Bean给删了
          appContext.getAutowireCapableBeanFactory().destroyBean(bean);
          appContext.getAutowireCapableBeanFactory().initializeBean(bean, name);
          return true;
       }
    }
    catch (RuntimeException e) {
       this.errors.put(name, e);
       throw e;
    }
    catch (Exception e) {
       this.errors.put(name, e);
       throw new IllegalStateException("Cannot rebind to " + name, e);
    }
    return false;
}

Value形式

原理：改变Bean实例化的方式，通过spring广播机制把Bean删除之后再重新实例化

Spring框架真是神奇，Bean的操作基本都可以进行定制

@RefreshScope
public class TestController {
    @Value("${fang.test}")
    private String configValue;

1. 在Spring Ioc容器中，不走寻常的创建Bean

else {
					String scopeName = mbd.getScope();
					if (!StringUtils.hasLength(scopeName)) {
						throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
					}
					Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
					}
					try {
						Object scopedInstance = scope.get(beanName, () -> {
							beforePrototypeCreation(beanName);
							try {
								return createBean(beanName, mbd, args);
							}
							finally {
								afterPrototypeCreation(beanName);
							}
						});
						beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new ScopeNotActiveException(beanName, scopeName, ex);
					}
				}
			}

在ContextRefresher直接对Bean的缓存管理器进行清除

总结

从这一个小功能能看出cloud基本都是基于boot

而配置动态更新这一功能，更是将Ioc容器玩出花来了

属实是springboot中Bean的最佳应用了