基于ZooKeeper實現(xiàn)隊列源碼

更新時間：2017年09月18日 15:43:17 作者：MassiveStars

這篇文章主要介紹了基于ZooKeeper實現(xiàn)隊列源碼的相關內(nèi)容，包括其實現(xiàn)原理和應用場景，以及對隊列的簡單介紹，具有一定參考價值，需要的朋友可以了解下。

實現(xiàn)原理

先進先出隊列是最常用的隊列，使用Zookeeper實現(xiàn)先進先出隊列就是在特定的目錄下創(chuàng)建PERSISTENT_EQUENTIAL節(jié)點，創(chuàng)建成功時Watcher通知等待的隊列，隊列刪除序列號最小的節(jié)點用以消費。此場景下Zookeeper的znode用于消息存儲，znode存儲的數(shù)據(jù)就是消息隊列中的消息內(nèi)容，SEQUENTIAL序列號就是消息的編號，按序取出即可。由于創(chuàng)建的節(jié)點是持久化的，所以不必擔心隊列消息的丟失問題。

隊列（Queue）

分布式隊列是通用的數(shù)據(jù)結(jié)構(gòu)，為了在 Zookeeper 中實現(xiàn)分布式隊列，首先需要指定一個 Znode 節(jié)點作為隊列節(jié)點（queue node），各個分布式客戶端通過調(diào)用 create() 函數(shù)向隊列中放入數(shù)據(jù)，調(diào)用create()時節(jié)點路徑名帶"qn-"結(jié)尾，并設置順序（sequence）節(jié)點標志。由于設置了節(jié)點的順序標志，新的路徑名具有以下字符串模式："_path-to-queue-node_/qn-X"，X 是唯一自增號。需要從隊列中獲取數(shù)據(jù)/移除數(shù)據(jù)的客戶端首先調(diào)用 getChildren() 函數(shù)，有數(shù)據(jù)則獲?。ǐ@取數(shù)據(jù)后可以刪除也可以不刪），沒有則在隊列節(jié)點（queue node）上將 watch 設置為 true，等待觸發(fā)并處理最小序號的節(jié)點（即從序號最小的節(jié)點中取數(shù)據(jù)）。

應用場景

Zookeeper隊列不太適合要求高性能的場合，但可以在數(shù)據(jù)量不大的情況下考慮使用。比如已在項目中使用Zookeeper又需要小規(guī)模的隊列應用，這時可以使用Zookeeper實現(xiàn)的隊列;畢竟引進一個消息中間件會增加系統(tǒng)的復雜性和運維的壓力。

詳細代碼

ZookeeperClient工具類

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 { 
 //-------------------------------------------------------------- 
 // 為避免連接還未完成就執(zhí)行zookeeper的get/create/exists操作引起的（KeeperErrorCode = ConnectionLoss) 
 // 這里等Zookeeper的連接完成才返回實例 
 //-------------------------------------------------------------- 
 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(); 
 //---------------------------------------------------- 
 // 確保隊列根目錄/QUEUE和當前隊列的目錄的存在 
 //---------------------------------------------------- 
 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()); 
  //---------------------------------------------------- 
  // 如果沒有消息節(jié)點，等待生產(chǎn)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); 
   } 
   //---------------------------------------------------- 
   // 消費隊列里序列號最小的消息 
   //---------------------------------------------------- 
   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) { 
  //---------------------------------------------------- 
  // 生產(chǎn)一條消息成功后通知一個等待線程 
  //---------------------------------------------------- 
  synchronized (mutex) { 
  mutex.notify(); 
  } 
 } 
 } 
 public void produce(byte[] data) throws KeeperException, InterruptedException, UnsupportedEncodingException { 
 //---------------------------------------------------- 
 // 確保當前隊列目錄存在 
 // 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(); 
 } 
}

測試

運行main方法，本機器的某次輸出結(jié)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

總結(jié)

以上就是本文有關于隊列和基于ZooKeeper實現(xiàn)隊列源碼介紹的全部內(nèi)容，希望對大家有所幫助。

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