基于ZooKeeper实现队列源码

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

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

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

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。

感谢朋友们对本站的支持！