zookeeper應用之分散式鎖Java實現
原文地址：http://blog.csdn.net/z69183787/article/details/79355829
zookeeper在專案中有很多應用，其中一個比較常見的的就是分散式鎖，zookeeper實現分散式鎖的原理是根據zookeeper建立的臨時有序節點，每次zookeeper在同一個目錄下建立的臨時有序節點是有序的，會自動累加，如果本次操作建立的節點在目錄內是最小節點，則獲得鎖，否則阻塞等待鎖，並且總是在前一個節點上註冊watcher監視前一個節點的釋放，較小的節點釋放後，等待的節點對應的操作獲得鎖，以此類推，程式碼簡單實現如下：
public class ZKDisLock {privatestatic final Logger SERVICE_LOG = LoggerFactory.getLogger(LogConstants.SERVICE_LOG);//鎖目錄private static final String BASE_PATH = "/disLock";private static final String SPLIT_FLAG = "_";private Integer sessionOut;private String zkHost;private ZooKeeper zooKeeper;//當前鎖節點名稱private String lockNode;//等待鎖節點名稱privateString waitNode;private CountDownLatch countDownLatch;public ZKDisLock(Integer sessionOut, String zkHost) {this.sessionOut = sessionOut;this.zkHost = zkHost;}//ZKDisLock初始化public void init() throws DisLockException {try {zooKeeper = new ZooKeeper(zkHost, sessionOut, new Watcher() {@Overridepublic voidprocess(WatchedEvent watchedEvent) {}});//判斷有無根目錄，沒有的話建立Stat stat = zooKeeper.exists(BASE_PATH, false);if (stat == null) {zooKeeper.create(BASE_PATH, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);}} catch (Exception e) {SERVICE_LOG.info("zk初始化失敗");throw new DisLockException("zk初始化失敗");}}//加鎖public void lock(String content) throws DisLockException {if (zooKeeper == null) {throw new DisLockException("zk未初始化");}try {//建立節點String itemName = zooKeeper.create(BASE_PATH + "/" + content + SPLIT_FLAG, null, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);//判斷節點是否是目錄中同一個content的最小節點if (isLowestNode(content, itemName)) {SERVICE_LOG.info("執行緒：" + Thread.currentThread().getId() + ",加鎖成功,節點名稱：" + lockNode);return;} else {SERVICE_LOG.info("執行緒：" + Thread.currentThread().getId() + ",等待鎖：" + waitNode);//不是最小節點，等待鎖釋放waitForLock(sessionOut);//鎖釋放後，再次判斷下是否是最小節點if (isLowestNode(content, itemName)) {SERVICE_LOG.info("執行緒：" + Thread.currentThread().getId() + ",獲得鎖,節點名稱：" + lockNode);return;}}} catch (Exception e) {SERVICE_LOG.error("加鎖異常");throw new DisLockException("加鎖異常");}
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