---

假设Nacos服务已经搭建完成

配置

• 新建service-config配置文件，9d0c9401-f575-4427-a982-eb8637a652b0为区别命名空间的ID，自动生成。
  

Demo搭建

• 引入依赖

<!-- nacos -->
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
            <version>2.1.3.RELEASE</version>
        </dependency>

• resources下新建 bootstrap.properties 配置文件，配置信息如下：

spring.cloud.nacos.config.server-addr=127.0.0.1:8848
spring.cloud.nacos.config.file-extension=yml
spring.application.name=service-config
spring.cloud.nacos.config.namespace=9d0c9401-f575-4427-a982-eb8637a652b0
# 项目启动nacos配置信息打印级别，info会打印出配置信息
logging.level.com.alibaba.cloud.nacos.client.NacosPropertySourceBuilder=warn

• 关键注解RefreshScope

@RestController
@RefreshScope
public class TestNacosController {
    

    @Value("${top.fsn.id}")
    private String id;

    @RequestMapping("test")
    public String test() {
    
        return id;
    }
}

RefreshScope 原理

该注解支持动态更新配置文件中数据，无需重启服务。另外，该注解及实现方式也是SpringCloud下，通过拓展Spring下的Scope（作用域）接口进行实现。其注解代码如下：

• 注解的代码很简单，可以看到它返回的是ScopedProxyMode（就姑且叫代理模型吧）对象。关于代理模型有如下四种类型(实际就三种)。

@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 enum ScopedProxyMode {
    

	/**
	 * Default typically equals {@link #NO}, unless a different default
	 * has been configured at the component-scan instruction level.
	 */
	// 与NO类型一样，表示不使用代理
	DEFAULT,

	/**
	 * Do not create a scoped proxy.
	 * <p>This proxy-mode is not typically useful when used with a
	 * non-singleton scoped instance, which should favor the use of the
	 * {@link #INTERFACES} or {@link #TARGET_CLASS} proxy-modes instead if it
	 * is to be used as a dependency.
	 */
	NO,

	/**
	 * Create a JDK dynamic proxy implementing <i>all</i> interfaces exposed by
	 * the class of the target object.
	 */
	 // 使用 jdk dynamic proxy(基于接口的代理)
	INTERFACES,

	/**
	 * Create a class-based proxy (uses CGLIB).
	 */
	 // 使用 CGLIB 做代理（基于目标类）
	TARGET_CLASS;

}

• RefreshScope 的实现，几个类结构如下，
  
• 再看看RefreshScope 类继承了GenericScope

public class RefreshScope extends GenericScope implements ApplicationContextAware,
		ApplicationListener<ContextRefreshedEvent>, Ordered

• 通过Debug可以知道启动时，调用onApplicationEvent 方法。在start方法有进行eagerlyInitialize初始化。
  
• 初始化的过程会获取一个name为scopedTarget.testNacosController

这个方法有一处不明白，讲道理，这个void方法，如果是我写，判断bean不为null，我直接return了，还getClass干嘛。。但是最近看过why大佬的一篇关于return null文章，顿时茅塞顿开。

if (bean != null) {bean.getClass();}

• 在getBean的时候有绕了一大圈：首先去到BeanFactory#getBean -> AbstractBeanFactory#getBean -> AbstractBeanFactory#doGetBean
  
• 在AbstractBeanFactory#doGetBean中，又通过如下方法，调用GenericScope #get方法，兜兜转转，又回到RefreshScope 的父类来了：

# AbstractBeanFactory#doGetBean
Object scopedInstance = scope.get(beanName, () -> {
    
							beforePrototypeCreation(beanName);

# GenericScope #get
@Override
	public Object get(String name, ObjectFactory<?> objectFactory) {
    
		BeanLifecycleWrapper value = this.cache.put(name,
				new BeanLifecycleWrapper(name, objectFactory));
		this.locks.putIfAbsent(name, new ReentrantReadWriteLock());
		try {
    
			return value.getBean();
		}
		catch (RuntimeException e) {
    
			this.errors.put(name, e);
			throw e;
		}
	}

• 可以看到我们这里用 @RefreshScope注解的bean最终被放到一个locks中，它的定义如下：

private ConcurrentMap<String, ReadWriteLock> locks = new ConcurrentHashMap<>();

• 每个bean在初始后之后，还需要为其添加一个监听器，在继续debug之后，就来到了：

NacosContextRefresher#registerNacosListenersForApplications

• 添加监听器时，又会触发Nacos的客户端ClientWorker#addListeners方法，然后又会把相关的配置信息同步到一个cacheMap中，后面监听配置是否有变化时，就从cacheMap中获取数据：

其中 tenant=9d0c9401-f575-4427-a982-eb8637a652b0，即命名空间随出来的字符串标识

public void addListeners(String dataId, String group, List<? extends Listener> listeners) {
    
        group = null2defaultGroup(group);
        CacheData cache = addCacheDataIfAbsent(dataId, group);
        for (Listener listener : listeners) {
    
            cache.addListener(listener);
        }
    }

```cpp
public CacheData addCacheDataIfAbsent(String dataId, String group, String tenant) throws NacosException {
    
       // ...
        synchronized (cacheMap) {
    
            CacheData cacheFromMap = getCache(dataId, group, tenant);
            if (null != cacheFromMap) {
    
                cache = cacheFromMap;
                // reset so that server not hang this check
                cache.setInitializing(true);
            } else {
    
                cache = new CacheData(configFilterChainManager, agent.getName(), dataId, group, tenant);
                // fix issue # 1317
                if (enableRemoteSyncConfig) {
    
                    String[] ct = getServerConfig(dataId, group, tenant, 3000L);
                    cache.setContent(ct[0]);
                }
            }
            
            Map<String, CacheData> copy = new HashMap<String, CacheData>(this.cacheMap.get());
            copy.put(key, cache);
            cacheMap.set(copy);
        }
        LOGGER.info("[{}] [subscribe] {}", agent.getName(), key);
        
        MetricsMonitor.getListenConfigCountMonitor().set(cacheMap.get().size());
        
        return cache;
    }

• 在监听到服务端配置时，则得益于ClientWork#LongPollingRunnable内部类。

class LongPollingRunnable implements Runnable {
    
        
      // ...
        
        @Override
        public void run() {
    
             // ...
    
            try {
    
                // check failover config
                // ...
                // check server config
                // ...
              
       }
    }

• 在ClientWorker初始化后，会初始化executor 和 executorService ，executor 每隔 10毫秒（？？有点奇怪 这么快的频率吗）启动 executorService 中的任务线程检查配置信息。

话说这种设计方式有点绕。。。

public ClientWorker(final HttpAgent agent, final ConfigFilterChainManager configFilterChainManager,
            final Properties properties) {
    
        this.agent = agent;
        this.configFilterChainManager = configFilterChainManager;
        
        // Initialize the timeout parameter
        
        init(properties);
        
        this.executor = Executors.newScheduledThreadPool(1, new ThreadFactory() {
    
            @Override
            public Thread newThread(Runnable r) {
    
                Thread t = new Thread(r);
                t.setName("com.alibaba.nacos.client.Worker." + agent.getName());
                t.setDaemon(true);
                return t;
            }
        });
        
        this.executorService = Executors
                .newScheduledThreadPool(Runtime.getRuntime().availableProcessors(), new ThreadFactory() {
    
                    @Override
                    public Thread newThread(Runnable r) {
    
                        Thread t = new Thread(r);
                        t.setName("com.alibaba.nacos.client.Worker.longPolling." + agent.getName());
                        t.setDaemon(true);
                        return t;
                    }
                });
        
        this.executor.scheduleWithFixedDelay(new Runnable() {
    
            @Override
            public void run() {
    
                try {
    
                    checkConfigInfo();
                } catch (Throwable e) {
    
                    LOGGER.error("[" + agent.getName() + "] [sub-check] rotate check error", e);
                }
            }
        }, 1L, 10L, TimeUnit.MILLISECONDS);
    }