根据04版补全程序更新P19双写程序。

src/main/java/com/zdjizhi/utils/zookeeper/DistributedLock.java

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+package com.zdjizhi.utils.zookeeper;
+
+import cn.hutool.log.Log;
+import cn.hutool.log.LogFactory;
+import org.apache.zookeeper.*;
+import org.apache.zookeeper.data.Stat;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.Lock;
+
+/**
+ * @author qidaijie
+ */
+public class DistributedLock implements Lock, Watcher {
+    private static final Log logger = LogFactory.get();
+
+    private ZooKeeper zk = null;
+    /**
+     * 根节点
+     */
+    private final String ROOT_LOCK = "/locks";
+    /**
+     * 竞争的资源
+     */
+    private String lockName;
+    /**
+     * 等待的前一个锁
+     */
+    private String waitLock;
+    /**
+     * 当前锁
+     */
+    private String currentLock;
+    /**
+     * 计数器
+     */
+    private CountDownLatch countDownLatch;
+
+    private int sessionTimeout = 2000;
+
+    private List<Exception> exceptionList = new ArrayList<Exception>();
+
+    /**
+     * 配置分布式锁
+     *
+     * @param config   连接的url
+     * @param lockName 竞争资源
+     */
+    public DistributedLock(String config, String lockName) {
+        this.lockName = lockName;
+        try {
+            // 连接zookeeper
+            zk = new ZooKeeper(config, sessionTimeout, this);
+            Stat stat = zk.exists(ROOT_LOCK, false);
+            if (stat == null) {
+                // 如果根节点不存在，则创建根节点
+                zk.create(ROOT_LOCK, new byte[0], ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
+            }
+        } catch (IOException | InterruptedException | KeeperException e) {
+            logger.error("Node already exists!");
+        }
+    }
+
+    // 节点监视器
+    @Override
+    public void process(WatchedEvent event) {
+        if (this.countDownLatch != null) {
+            this.countDownLatch.countDown();
+        }
+    }
+
+    @Override
+    public void lock() {
+        if (exceptionList.size() > 0) {
+            throw new LockException(exceptionList.get(0));
+        }
+        try {
+            if (this.tryLock()) {
+                logger.info(Thread.currentThread().getName() + " " + lockName + "获得了锁");
+            } else {
+                // 等待锁
+                waitForLock(waitLock, sessionTimeout);
+            }
+        } catch (InterruptedException | KeeperException e) {
+            logger.error("获取锁异常" + e);
+        }
+    }
+
+    @Override
+    public boolean tryLock() {
+        try {
+            String splitStr = "_lock_";
+            if (lockName.contains(splitStr)) {
+                throw new LockException("锁名有误");
+            }
+            // 创建临时有序节点
+            currentLock = zk.create(ROOT_LOCK + "/" + lockName + splitStr, new byte[0],
+                    ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
+            // 取所有子节点
+            List<String> subNodes = zk.getChildren(ROOT_LOCK, false);
+            // 取出所有lockName的锁
+            List<String> lockObjects = new ArrayList<String>();
+            for (String node : subNodes) {
+                String tmpNode = node.split(splitStr)[0];
+                if (tmpNode.equals(lockName)) {
+                    lockObjects.add(node);
+                }
+            }
+            Collections.sort(lockObjects);
+            // 若当前节点为最小节点，则获取锁成功
+            if (currentLock.equals(ROOT_LOCK + "/" + lockObjects.get(0))) {
+                return true;
+            }
+            // 若不是最小节点，则找到自己的前一个节点
+            String prevNode = currentLock.substring(currentLock.lastIndexOf("/") + 1);
+            waitLock = lockObjects.get(Collections.binarySearch(lockObjects, prevNode) - 1);
+        } catch (InterruptedException | KeeperException e) {
+            logger.error("获取锁过程异常" + e);
+        }
+        return false;
+    }
+
+
+    @Override
+    public boolean tryLock(long timeout, TimeUnit unit) {
+        try {
+            if (this.tryLock()) {
+                return true;
+            }
+            return waitForLock(waitLock, timeout);
+        } catch (KeeperException | InterruptedException | RuntimeException e) {
+            logger.error("判断是否锁定异常" + e);
+        }
+        return false;
+    }
+
+    // 等待锁
+    private boolean waitForLock(String prev, long waitTime) throws KeeperException, InterruptedException {
+        Stat stat = zk.exists(ROOT_LOCK + "/" + prev, true);
+
+        if (stat != null) {
+            this.countDownLatch = new CountDownLatch(1);
+            // 计数等待，若等到前一个节点消失，则precess中进行countDown，停止等待，获取锁
+            this.countDownLatch.await(waitTime, TimeUnit.MILLISECONDS);
+            this.countDownLatch = null;
+        }
+        return true;
+    }
+
+    @Override
+    public void unlock() {
+        try {
+            zk.delete(currentLock, -1);
+            currentLock = null;
+            zk.close();
+        } catch (InterruptedException | KeeperException e) {
+            logger.error("关闭锁异常" + e);
+        }
+    }
+
+    @Override
+    public Condition newCondition() {
+        return null;
+    }
+
+    @Override
+    public void lockInterruptibly() throws InterruptedException {
+        this.lock();
+    }
+
+
+    public class LockException extends RuntimeException {
+        private static final long serialVersionUID = 1L;
+
+        public LockException(String e) {
+            super(e);
+        }
+
+        public LockException(Exception e) {
+            super(e);
+        }
+    }
+
+}