Nacos源码系列之@RefreshScope

• • 一、背景
  • 二、如何实现
  • • 1、初识RefreshScope
    • • （1）ScopedProxyMode
      • （2）@Scope("refresh")
    • 2、RefreshScope
    • 3、RefreshScope 刷新
  • 三、小结

我们在使用Nacos做配置自动刷新时，会使用@RefreshScope注解。如：

@RefreshScope
@Configuration
public class AsyncExceptionHandler implements AsyncConfigurer {
}


@Configuration
public class DataSourceConfig {
    @Bean
    @Primary
    @RefreshScope
    @ConfigurationProperties(ignoreUnknownFields = false, prefix = "spring.datasource.hikari")
    public DataSource dataSource() {
        return new SnooperDataSource();
    }
}

那么，@RefreshScope时候如何实现配置自动更新的呢？

在spring-cloud-context包下，路径：org.springframework.cloud.context.config.annotation.RefreshScope。

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Scope("refresh")
@Documented
public @interface RefreshScope {
    ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;
}

代理模式类型：

• 不使用代理
• 接口，使用JDK代理 JdkDynamicAopProxy
• 类，使用CGLIB代理 CglibAopProxy

public enum ScopedProxyMode {
    DEFAULT,
    NO,
    INTERFACES,
    TARGET_CLASS;

    private ScopedProxyMode() {
    }
}

scopeName为refresh，

@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Scope {
    @AliasFor("scopeName")
    String value() default "";

    @AliasFor("value")
    String scopeName() default "";

    ScopedProxyMode proxyMode() default ScopedProxyMode.DEFAULT;
}

加上@Scope注解的实例，都是由Scope自己创建的。RefreshScope是在内建缓存中获取的。

private final Map scopes = new LinkedHashMap(8);

AbstractBeanFactory#getBean()
...
String scopeName = mbd.getScope();
 if (!StringUtils.hasLength(scopeName)) {
     throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
 }

 Scope 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, () -> {
         this.beforePrototypeCreation(beanName);

         Object var4;
         try {
             var4 = this.createBean(beanName, mbd, args);
         } finally {
             this.afterPrototypeCreation(beanName);
         }

         return var4;
     });
     beanInstance = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
 } catch (IllegalStateException var30) {
     throw new ScopeNotActiveException(beanName, scopeName, var30);
 }

RefreshScope继承自GenericScope，GenericScope实现了Scope接口。

//RefreshScope
public class RefreshScope extends GenericScope implements ApplicationContextAware, ApplicationListener, Ordered {
	 
	 public RefreshScope() {
        super.setName("refresh");
    }
	
}

//GenericScope
public class GenericScope implements Scope, BeanFactoryPostProcessor, BeanDefinitionRegistryPostProcessor, DisposableBean {

	
}

get() 获取bean方法：
从缓存中获取，如果缓存中存在返回缓存中数据，否则就添加到缓存。

//GenericScope
public Object get(String name, ObjectFactory objectFactory) {
        GenericScope.BeanLifecycleWrapper value = this.cache.put(name, new GenericScope.BeanLifecycleWrapper(name, objectFactory));
        this.locks.putIfAbsent(name, new ReentrantReadWriteLock());

        try {
            return value.getBean();
        } catch (RuntimeException var5) {
            this.errors.put(name, var5);
            throw var5;
        }
    }
    
  public GenericScope.BeanLifecycleWrapper put(String name, GenericScope.BeanLifecycleWrapper value) {
            return (GenericScope.BeanLifecycleWrapper)this.cache.put(name, value);
   }
   
  public Object put(String name, Object value) {
        Object result = this.cache.putIfAbsent(name, value);
        return result != null ? result : value;
  }

public Object getBean() {
     if (this.bean == null) {
         synchronized(this.name) {
             if (this.bean == null) {
                 this.bean = this.objectFactory.getObject();
             }
         }
     }

     return this.bean;
 }

RefreshScope#refreshAll()
两个操作：destroy()和publishEvent()。

    @ManagedOperation(
        description = "Dispose of the current instance of all beans in this scope and force a refresh on next method execution."
    )
    public void refreshAll() {
        super.destroy();
        this.context.publishEvent(new RefreshScopeRefreshedEvent());
    }

//清空wrapper
    public void destroy() {
        List errors = new ArrayList();
        Collection wrappers = this.cache.clear();
        Iterator var3 = wrappers.iterator();

        while(var3.hasNext()) {
            GenericScope.BeanLifecycleWrapper wrapper = (GenericScope.BeanLifecycleWrapper)var3.next();

            try {
                Lock lock = ((ReadWriteLock)this.locks.get(wrapper.getName())).writeLock();
                lock.lock();

                try {
                    wrapper.destroy();
                } finally {
                    lock.unlock();
                }
            } catch (RuntimeException var10) {
                errors.add(var10);
            }
        }

        if (!errors.isEmpty()) {
            throw wrapIfNecessary((Throwable)errors.get(0));
        } else {
            this.errors.clear();
        }
    }
    
public void destroy() {
    if (this.callback != null) {
        synchronized(this.name) {
            Runnable callback = this.callback;
            if (callback != null) {
                callback.run();
            }

            this.callback = null;
            this.bean = null;
        }
    }
}

我们可以通过以下两种方式发起刷新配置：

• 访问接口 http://localhost:8080/actuator/refresh
• 监听RefreshEvent事件

1、Spring提供了bean的自定义获取和创建逻辑，Scope bean。
2、两种方式：推和拉。
推——事件订阅模式。监听事件后，若有变更通知，会自动推送。
拉——请求接口获取变更信息。
3、缓存cache。