ReleaseMessageScanner：扫描变更配置，触发监听者们

配置变更监听机制

最新推荐文章于 2024-02-04 08:49:10 发布

原创最新推荐文章于 2024-02-04 08:49:10 发布 · 291 阅读

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本文介绍了一个配置变更监听机制的实现，通过定时扫描数据库中的配置变更并通知监听者。该机制包括启动定时任务、查询数据库获取变更配置、更新最大配置ID记录及通知监听者等步骤。

ReleaseMessageScanner：扫描变更配置，触发监听者们

目录
- 概述

LD is tigger forever，CG are not brothers forever， throw the pot and shine forever.
Modesty is not false, solid is not naive, treacherous but not deceitful, stay with good people, and stay away from poor people.
talk is cheap, show others the code and KPI， Keep progress，make a better result.
Survive during the day and develop at night。

public class ReleaseMessageScanner implements InitializingBean {
  private static final Logger logger = LoggerFactory.getLogger(ReleaseMessageScanner.class);
  @Autowired
  private BizConfig bizConfig;
  @Autowired
  private ReleaseMessageRepository releaseMessageRepository;
  private int databaseScanInterval;
  private List<ReleaseMessageListener> listeners;
  private ScheduledExecutorService executorService;
  private long maxIdScanned;
 
  public ReleaseMessageScanner() {
    listeners = Lists.newCopyOnWriteArrayList();
    executorService = Executors.newScheduledThreadPool(1, ApolloThreadFactory
        .create("ReleaseMessageScanner", true));
  }
 
  @Override
  public void afterPropertiesSet() throws Exception {
  	//定时任务频率，默认1000ms
    databaseScanInterval = bizConfig.releaseMessageScanIntervalInMilli();
    //最大的ReleaseMessage编号
    maxIdScanned = loadLargestMessageId();
    //每秒走一次，扫描消息定时
    executorService.scheduleWithFixedDelay((Runnable) () -> {
      Transaction transaction = Tracer.newTransaction("Apollo.ReleaseMessageScanner", "scanMessage");
      try {
        scanMessages();
        transaction.setStatus(Transaction.SUCCESS);
      } catch (Throwable ex) {
        transaction.setStatus(ex);
        logger.error("Scan and send message failed", ex);
      } finally {
        transaction.complete();
      }
    }, databaseScanInterval, databaseScanInterval, TimeUnit.MILLISECONDS);
 
  }
 

```java

  private long loadLargestMessageId() {
    ReleaseMessage releaseMessage = releaseMessageRepository.findTopByOrderByIdDesc();
    return releaseMessage == null ? 0 : releaseMessage.getId();
  }
 
  /**
   * Notify listeners with messages loaded
   * @param messages
   */
  private void fireMessageScanned(List<ReleaseMessage> messages) {
    for (ReleaseMessage message : messages) {
    	//将每条消息循环通知所有订阅者
      for (ReleaseMessageListener listener : listeners) {
        try {
        	//触发监听
          listener.handleMessage(message, Topics.APOLLO_RELEASE_TOPIC);
        } catch (Throwable ex) {
          Tracer.logError(ex);
          logger.error("Failed to invoke message listener {}", listener.getClass(), ex);
        }
      }
    }

总结：
1、启动一个定时任务（每秒一次）
2.根据最大编号查询数据库500条（按id倒叙）
3、设置最新的最大编号
4.触发监听者们–还记得下面这个监听吗
com.ctrip.framework.apollo.configservice.ConfigServiceAutoConfiguration.MessageScannerConfiguration#releaseMessageScanner

 /**
	   * 监听器注册，namespaces变更后接收消息
	   * @return
	   */
    @Bean
    public ReleaseMessageScanner releaseMessageScanner() {
      ReleaseMessageScanner releaseMessageScanner = new ReleaseMessageScanner();
      //0. handle release message cache
      releaseMessageScanner.addMessageListener(releaseMessageServiceWithCache);
      //1. handle gray release rule
      releaseMessageScanner.addMessageListener(grayReleaseRulesHolder);
      //2. handle server cache
      releaseMessageScanner.addMessageListener(configService);
      releaseMessageScanner.addMessageListener(configFileController);
      //3. notify clients
      releaseMessageScanner.addMessageListener(notificationControllerV2);
      releaseMessageScanner.addMessageListener(notificationController);
      return releaseMessageScanner;
    }





# 小结
NotificationControllerV2：notifications/v2：实现长轮循，监听配置变更、返回，结束长轮循
# 参考资料和推荐阅读
1.链接: [参考资料](https://blog.youkuaiyun.com/qq_26418435/article/details/102601603).