zookeeper基本api

zookeeper api及 应用实例:

Zookeeper 作为一个分布式的服务框架，主要用来解决分布式集群中应用系统的一致性问题，它能提供基于类似于文件系统的目录节点树方式的数据存储，但是 Zookeeper 并不是用来专门存储数据的，它的作用主要是用来维护和监控你存储的数据的状态变化。通过监控这些数据状态的变化，从而可以达到基于数据的集群管理，后面将会详细介绍 Zookeeper 能够解决的一些典型问题，这里先介绍一下，Zookeeper 的操作接口和简单使用示例。

api:

mavan:

     <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.6</version>
      </dependency>

package com.twodfire.meta.tool;

import org.apache.zookeeper.*;

import java.io.IOException;

/**
 * Created by chenkaidong on 2017/7/4.
 */
public class ZookeeperCli {

    private static String CLIENT_PORT = "2181";

    public static void main(String[] args) throws KeeperException, InterruptedException, IOException {


        // 创建一个与服务器的连接
        ZooKeeper zk = new ZooKeeper("localhost:" + CLIENT_PORT,
                2000, new Watcher() {
            // 监控所有被触发的事件
            public void process(WatchedEvent event) {
                System.out.println("已经触发了" + event.getType() + "事件！");
            }
        });
        // 创建一个目录节点
        //zk.create("/testRootPath", "testRootData".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,
          //      CreateMode.PERSISTENT);
        // 创建一个子目录节点
        zk.create("/testRootPath/testChildPathOne", "testChildDataOne".getBytes(),
                ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
        System.out.println(new String(zk.getData("/testRootPath",false,null)));
        // 取出子目录节点列表
        System.out.println(zk.getChildren("/testRootPath",true));
        // 修改子目录节点数据
        zk.setData("/testRootPath/testChildPathOne","modifyChildDataOne".getBytes(),-1);
        System.out.println("目录节点状态：["+zk.exists("/testRootPath",true)+"]");
        // 创建另外一个子目录节点
        zk.create("/testRootPath/testChildPathTwo", "testChildDataTwo".getBytes(),
                ZooDefs.Ids.OPEN_ACL_UNSAFE,CreateMode.PERSISTENT);
        System.out.println(new String(zk.getData("/testRootPath/testChildPathTwo",true,null)));
        // 删除子目录节点
        zk.delete("/testRootPath/testChildPathTwo",-1);
        zk.delete("/testRootPath/testChildPathOne",-1);
        // 删除父目录节点
        zk.delete("/testRootPath",-1);
        // 关闭连接
        zk.close();



    }
}

leader election:

void findLeader() throws InterruptedException { 
        byte[] leader = null; 
        try { 
            leader = zk.getData(root + "/leader", true, null); 
        } catch (Exception e) { 
            logger.error(e); 
        } 
        if (leader != null) { 
            following(); 
        } else { 
            String newLeader = null; 
            try { 
                byte[] localhost = InetAddress.getLocalHost().getAddress(); 
                newLeader = zk.create(root + "/leader", localhost, 
                ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL); 
            } catch (Exception e) { 
                logger.error(e); 
            } 
            if (newLeader != null) { 
                leading(); 
            } else { 
                mutex.wait(); 
            } 
        } 
    } 

锁:

void getLock() throws KeeperException, InterruptedException{ 
        List<String> list = zk.getChildren(root, false); 
        String[] nodes = list.toArray(new String[list.size()]); 
        Arrays.sort(nodes); 
        if(myZnode.equals(root+"/"+nodes[0])){ 
            doAction(); 
        } 
        else{ 
            waitForLock(nodes[0]); 
        } 
    } 
    void waitForLock(String lower) throws InterruptedException, KeeperException {
        Stat stat = zk.exists(root + "/" + lower,true); 
        if(stat != null){ 
            mutex.wait(); 
        } 
        else{ 
            getLock(); 
        } 
    }

队列:

void addQueue() throws KeeperException, InterruptedException{ 
        zk.exists(root + "/start",true); 
        zk.create(root + "/" + name, new byte[0], Ids.OPEN_ACL_UNSAFE, 
        CreateMode.EPHEMERAL_SEQUENTIAL); 
        synchronized (mutex) { 
            List<String> list = zk.getChildren(root, false); 
            if (list.size() < size) { 
                mutex.wait(); 
            } else { 
                zk.create(root + "/start", new byte[0], Ids.OPEN_ACL_UNSAFE,
                 CreateMode.PERSISTENT); 
            } 
        } 
 }

public void process(WatchedEvent event) { 
        if(event.getPath().equals(root + "/start") &&
         event.getType() == Event.EventType.NodeCreated){ 
            System.out.println("得到通知"); 
            super.process(event); 
            doAction(); 
        } 
    }

FIFO队列:

boolean produce(int i) throws KeeperException, InterruptedException{ 
        ByteBuffer b = ByteBuffer.allocate(4); 
        byte[] value; 
        b.putInt(i); 
        value = b.array(); 
        zk.create(root + "/element", value, ZooDefs.Ids.OPEN_ACL_UNSAFE, 
                    CreateMode.PERSISTENT_SEQUENTIAL); 
        return true; 
    }

int consume() throws KeeperException, InterruptedException{ 
        int retvalue = -1; 
        Stat stat = null; 
        while (true) { 
            synchronized (mutex) { 
                List<String> list = zk.getChildren(root, true); 
                if (list.size() == 0) { 
                    mutex.wait(); 
                } else { 
                    Integer min = new Integer(list.get(0).substring(7)); 
                    for(String s : list){ 
                        Integer tempValue = new Integer(s.substring(7)); 
                        if(tempValue < min) min = tempValue; 
                    } 
                    byte[] b = zk.getData(root + "/element" + min,false, stat); 
                    zk.delete(root + "/element" + min, 0); 
                    ByteBuffer buffer = ByteBuffer.wrap(b); 
                    retvalue = buffer.getInt(); 
                    return retvalue; 
                } 
            } 
        } 
 }