实现原理
先进先出队列是最常用的队列，使用Zookeeper实现先进先出队列就是在特定的目录下创建PERSISTENT_EQUENTIAL节点，创建成功时Watcher通知等待的队列，队列删除序列号最小的节点用以消费。此场景下Zookeeper的znode用于消息存储，znode存储的数据就是消息队列中的消息内容，SEQUENTIAL序列号就是消息的编号，按序取出即可。由于创建的节点是持久化的，所以不必担心队列消息的丢失问题。
队列（Queue）
分布式队列是通用的数据结构，为了在 Zookeeper 中实现分布式队列，首先需要指定一个 Znode 节点作为队列节点（queue node）， 各个分布式客户端通过调用 create() 函数向队列中放入数据，调用create()时节点路径名带"qn-"结尾，并设置顺序（sequence）节点标志。 由于设置了节点的顺序标志，新的路径名具有以下字符串模式："_path-to-queue-node_/qn-X"，X 是唯一自增号。需要从队列中获取数据/移除数据的客户端首先调用 getChildren() 函数，有数据则获取（获取数据后可以删除也可以不删），没有则在队列节点（queue node）上将 watch 设置为 true，等待触发并处理最小序号的节点（即从序号最小的节点中取数据）。
应用场景
Zookeeper队列不太适合要求高性能的场合，但可以在数据量不大的情况下考虑使用。比如已在项目中使用Zookeeper又需要小规模的队列应用，这时可以使用Zookeeper实现的队列;毕竟引进一个消息中间件会增加系统的复杂性和运维的压力。
详细代码
ZookeeperClient工具类
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package org.massive.common; import org.apache.zookeeper.WatchedEvent; import org.apache.zookeeper.Watcher; import org.apache.zookeeper.ZooKeeper; import java.io.IOException; import java.util.concurrent.CountDownLatch; import java.util.concurrent.TimeUnit; /** * Created by Massive on 2016/12/18. */public class ZooKeeperClient { private static String connectionString = "localhost:2181"; private static int sessionTimeout = 10000; public static ZooKeeper getInstance() throws IOException, InterruptedException { //-------------------------------------------------------------- // 为避免连接还未完成就执行zookeeper的get/create/exists操作引起的（KeeperErrorCode = ConnectionLoss) // 这里等Zookeeper的连接完成才返回实例 //-------------------------------------------------------------- final CountDownLatch connectedSignal = new CountDownLatch(1); ZooKeeper zk = new ZooKeeper(connectionString, sessionTimeout, new Watcher() { @Override public void process(WatchedEvent event) { if (event.getState() == Event.KeeperState.SyncConnected) { connectedSignal.countDown(); } else if (event.getState() == Event.KeeperState.Expired) { } } }); connectedSignal.await(sessionTimeout, TimeUnit.MILLISECONDS); return zk; } public static int getSessionTimeout() { return sessionTimeout; } public static void setSessionTimeout(int sessionTimeout) { ZooKeeperClient.sessionTimeout = sessionTimeout; } } |
ZooKeeperQueue
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package org.massive.queue; import org.apache.commons.lang3.RandomUtils; import org.apache.zookeeper.*; import org.apache.zookeeper.data.Stat; import org.massive.common.ZooKeeperClient; import java.io.IOException; import java.io.UnsupportedEncodingException; import java.util.List; import java.util.SortedSet; import java.util.TreeSet; /** * Created by Allen on 2016/12/22. */public class ZooKeeperQueue { private ZooKeeper zk; private int sessionTimeout; private static byte[] ROOT_QUEUE_DATA = {0x12,0x34}; private static String QUEUE_ROOT = "/QUEUE"; private String queueName; private String queuePath; private Object mutex = new Object(); public ZooKeeperQueue(String queueName) throws IOException, KeeperException, InterruptedException { this.queueName = queueName; this.queuePath = QUEUE_ROOT + "/" + queueName; this.zk = ZooKeeperClient.getInstance(); this.sessionTimeout = zk.getSessionTimeout(); //---------------------------------------------------- // 确保队列根目录/QUEUE和当前队列的目录的存在 //---------------------------------------------------- ensureExists(QUEUE_ROOT); ensureExists(queuePath); } public byte[] consume() throws InterruptedException, KeeperException, UnsupportedEncodingException { List<String> nodes = null; byte[] returnVal = null; Stat stat = null; do { synchronized (mutex) { nodes = zk.getChildren(queuePath, new ProduceWatcher()); //---------------------------------------------------- // 如果没有消息节点，等待生产者的通知 //---------------------------------------------------- if (nodes == null || nodes.size() == 0) { mutex.wait(); } else { SortedSet<String> sortedNode = new TreeSet<String>(); for (String node : nodes) { sortedNode.add(queuePath + "/" + node); } //---------------------------------------------------- // 消费队列里序列号最小的消息 //---------------------------------------------------- String first = sortedNode.first(); returnVal = zk.getData(first, false, stat); zk.delete(first, -1); System.out.print(Thread.currentThread().getName() + " "); System.out.print("consume a message from queue：" + first); System.out.println(", message data is: " + new String(returnVal,"UTF-8")); return returnVal; } } } while (true); } class ProduceWatcher implements Watcher { @Override public void process(WatchedEvent event) { //---------------------------------------------------- // 生产一条消息成功后通知一个等待线程 //---------------------------------------------------- synchronized (mutex) { mutex.notify(); } } } public void produce(byte[] data) throws KeeperException, InterruptedException, UnsupportedEncodingException { //---------------------------------------------------- // 确保当前队列目录存在 // example: /QUEUE/queueName //---------------------------------------------------- ensureExists(queuePath); String node = zk.create(queuePath + "/", data, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT_SEQUENTIAL); System.out.print(Thread.currentThread().getName() + " "); System.out.print("produce a message to queue：" + node); System.out.println(" , message data is: " + new String(data,"UTF-8")); } public void ensureExists(String path) { try { Stat stat = zk.exists(path, false); if (stat == null) { zk.create(path, ROOT_QUEUE_DATA, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT); } } catch (KeeperException e) { e.printStackTrace(); } catch (InterruptedException e) { e.printStackTrace(); } } public static void main(String[] args) throws IOException, InterruptedException, KeeperException { String queueName = "test"; final ZooKeeperQueue queue = new ZooKeeperQueue(queueName); for (int i = 0; i < 10; i++) { new Thread(new Runnable() { @Override public void run() { try { queue.consume(); System.out.println("--------------------------------------------------------"); System.out.println(); } catch (InterruptedException e) { e.printStackTrace(); } catch (KeeperException e) { e.printStackTrace(); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } } }).start(); } new Thread(new Runnable() { @Override public void run() { for (int i = 0; i < 10; i++) { try { Thread.sleep(RandomUtils.nextInt(100 * i, 200 * i)); queue.produce(("massive" + i).getBytes()); } catch (InterruptedException e) { e.printStackTrace(); } catch (KeeperException e) { e.printStackTrace(); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } } } },"Produce-thread").start(); } } |
测试
运行main方法，本机器的某次输出结果
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Produce-thread produce a message to queue：/QUEUE/test/0000000000 , message data is: massive0 Thread-8 consume a message from queue：/QUEUE/test/0000000000, message data is: massive0 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000001 , message data is: massive1 Thread-6 consume a message from queue：/QUEUE/test/0000000001, message data is: massive1 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000002 , message data is: massive2 Thread-3 consume a message from queue：/QUEUE/test/0000000002, message data is: massive2 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000003 , message data is: massive3 Thread-0 consume a message from queue：/QUEUE/test/0000000003, message data is: massive3 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000004 , message data is: massive4 Thread-5 consume a message from queue：/QUEUE/test/0000000004, message data is: massive4 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000005 , message data is: massive5 Thread-2 consume a message from queue：/QUEUE/test/0000000005, message data is: massive5 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000006 , message data is: massive6 Thread-4 consume a message from queue：/QUEUE/test/0000000006, message data is: massive6 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000007 , message data is: massive7 Thread-9 consume a message from queue：/QUEUE/test/0000000007, message data is: massive7 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000008 , message data is: massive8 Thread-7 consume a message from queue：/QUEUE/test/0000000008, message data is: massive8 -------------------------------------------------------- Produce-thread produce a message to queue：/QUEUE/test/0000000009 , message data is: massive9 Thread-1 consume a message from queue：/QUEUE/test/0000000009, message data is: massive9 |
总结
以上就是本文有关于队列和基于ZooKeeper实现队列源码介绍的全部内容，希望对大家有所帮助。
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