一文带你理解@RefreshScope注解实现动态刷新原理

/**
 * Convenience annotation to put a <code>@Bean</code> definition in
 * {@link org.springframework.cloud.context.scope.refresh.RefreshScope refresh scope}.
 * Beans annotated this way can be refreshed at runtime and any components that are using
 * them will get a new instance on the next method call, fully initialized and injected
 * with all dependencies.
 *
 * @author Dave Syer
 *
 */
@Target({ ElementType.TYPE, ElementType.METHOD })
@Retention(RetentionPolicy.RUNTIME)
@Scope("refresh")
@Documented
public @interface RefreshScope {
	/**
	 * @see Scope#proxyMode()
	 * @return proxy mode
	 */
	ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;
}

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
protected <T> T doGetBean(
			String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly)
			throws BeansException {
				// 如果scope是单例的情况, 这里不进行分析
				if (mbd.isSingleton()) {
				 .....
				}
                // 如果scope是prototype的情况, 这里不进行分析
				else if (mbd.isPrototype()) {
					......
				}
                // 如果scope是其他的情况，本例中是reresh
				else {
					String scopeName = mbd.getScope();
					if (!StringUtils.hasLength(scopeName)) {
						throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
					}
                    // 获取refresh scope的实现类RefreshScope，这个类在哪里注入，我们后面讲
					Scope scope = this.scopes.get(scopeName);
					if (scope == null) {
						throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
					}
					try {
                        // 这边是获取bean,调用的是RefreshScope中的的方法
						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);
					}
				}
			}
			catch (BeansException ex) {
				beanCreation.tag("exception", ex.getClass().toString());
				beanCreation.tag("message", String.valueOf(ex.getMessage()));
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
			finally {
				beanCreation.end();
			}
		}
		return adaptBeanInstance(name, beanInstance, requiredType);
	}
}

public class GenericScope
		implements Scope, BeanFactoryPostProcessor, BeanDefinitionRegistryPostProcessor, DisposableBean {
                 @Override
  public Object get(String name, ObjectFactory<?> objectFactory) {
		// 将bean添加到缓存cache中
        BeanLifecycleWrapper value = this.cache.put(name, new BeanLifecycleWrapper(name, objectFactory));
		this.locks.putIfAbsent(name, new ReentrantReadWriteLock());
		try {
            // 调用下面的getBean方法
			return value.getBean();
		}
		catch (RuntimeException e) {
			this.errors.put(name, e);
			throw e;
		}
	}       
private static class BeanLifecycleWrapper {
		public Object getBean() {
            // 如果bean为空，则创建bean
			if (this.bean == null) {
				synchronized (this.name) {
					if (this.bean == null) {
						this.bean = this.objectFactory.getObject();
					}
				}
			}
            // 否则返回之前创建好的bean
			return this.bean;
		}
            }
        }

public class RefreshEventListener implements SmartApplicationListener {
........
	public void handle(RefreshEvent event) {
		if (this.ready.get()) { // don't handle events before app is ready
			log.debug("Event received " + event.getEventDesc());
            // 会调用refresh方法，进行刷新
			Set<String> keys = this.refresh.refresh();
			log.info("Refresh keys changed: " + keys);
		}
	}
}
// 这个是ContextRefresher类中的刷新方法
public synchronized Set<String> refresh() {
        // 刷新spring的envirionment 变量配置
		Set<String> keys = refreshEnvironment();
        // 刷新其他scope
		this.scope.refreshAll();
		return keys;
	}

public class RefreshScope extends GenericScope
		implements ApplicationContextAware, ApplicationListener<ContextRefreshedEvent>, Ordered {
	@ManagedOperation(description = "Dispose of the current instance of all beans "
			+ "in this scope and force a refresh on next method execution.")
	public void refreshAll() {
		// 调用父类的destroy
        super.destroy();
		this.context.publishEvent(new RefreshScopeRefreshedEvent());
	}
}
@Override
	public void destroy() {
		List<Throwable> errors = new ArrayList<Throwable>();
		Collection<BeanLifecycleWrapper> wrappers = this.cache.clear();
		for (BeanLifecycleWrapper wrapper : wrappers) {
			try {
				Lock lock = this.locks.get(wrapper.getName()).writeLock();
				lock.lock();
				try {
                    // 这里主要就是把之前的bean设置为null, 就会重新走createBean的流程了
					wrapper.destroy();
				}
				finally {
					lock.unlock();
				}
			}
			catch (RuntimeException e) {
				errors.add(e);
			}
		}
		if (!errors.isEmpty()) {
			throw wrapIfNecessary(errors.get(0));
		}
		this.errors.clear();
	}