zookeeper实现分布式缓存

在分布式环境下如何让多个jvm进程内共享数据？

通过zookeeper简单实现

环境：zookeeper3.6.2+springboot2.2.10

• pom.xml

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency
  <dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.6.2</version>
  </dependency>
</dependencies>

• application.yml

server:
  port: 9881
---
zk:
  connectString: localhost:2181,localhost:2182,localhost:2183
  timeout: 3000
  config:
    path: /config/ids

• 配置类

@Configuration
public class ZKConfig {
	
  private static Logger logger = LoggerFactory.getLogger(ZKConfig.class) ;
	
  @Value("${zk.connectString}")
  private String connectString ;
  @Value("${zk.timeout}")
  private Integer timeout ;
  @Bean
  public ZooKeeper zookeeper() {
    ZooKeeper zookeeper = null; 
    try {
      CountDownLatch cdl = new CountDownLatch(1);
      logger.info("zk准备连接: {}", connectString) ;
      zookeeper = new ZooKeeper(connectString, timeout, event -> {
       if (event.getState() == Event.KeeperState.SyncConnected) {
          logger.info("zk服务器连接成功");
          cdl.countDown() ; 
        }
      }) ;
      cdl.await() ;
    } catch(Exception e) {
      e.printStackTrace() ; 
    }
    return zookeeper ;
  }
	
  @Configuration
  public static class WatchNodeData implements InitializingBean {
		
    public static Set<String> cache = new HashSet<>() ; 
		
    @Resource
    private ZooKeeper zk ;
    @Value("${zk.config.path}")
    private String path ;
		
    @Override
    public void afterPropertiesSet() throws Exception {
      if (zk.exists(path, null) == null) {
        zk.create(path, null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT) ;
      }
      // PERSISTENT是不监听子孙节点，PERSISTENT_RECURSIVE是递归监听子孙节点
      zk.addWatch(path, new NodeIdWatch(zk), AddWatchMode.PERSISTENT_RECURSIVE) ;
    }
		
  private static class NodeIdWatch implements Watcher {
    private ZooKeeper zk ;
    public NodeIdWatch(ZooKeeper zk) {
      this.zk = zk ;
    }
    @Override
    public void process(WatchedEvent event) {
      switch (event.getType()) {
        case NodeDataChanged:
          try {
            String val = new String(this.zk.getData(event.getPath(), false, null)) ;
            logger.info("节点{} 数据发生变化, 当前值：{}", event.getPath(), val);
            WatchNodeData.cache.add(val) ;
          } catch (Exception e) {
            e.printStackTrace();
          }
          break ;
        case NodeCreated:
          logger.info("创建了节点：{}", event.getPath());
          break ;
        case NodeChildrenChanged:
          logger.info("子节点发生了变化：{}", event.getPath());
          break;
        default:
          break;
      }
    }
  }
}
}

这样我们监听节点数据的变化即可，只要有变化就添加到Set集合中。我们这里处理的小数据量可以这么玩，如果是海量数据肯定不能通过jvm来缓存数据。

至于zookeeper设置值，我们可以调用zk.setData即可，一旦设置了 我们这里就可以监听到，所以集群的服务都能收到。

完毕！！！