zookeeper 实战案例分享：cruator客户端编程

上两篇介绍了zookeeper服务器端的安装和配置，今天分享下利用zookeeper客户端编程来实现配置文件的统一管理，包括文件添加、删除、更新的同步。

比如，连接数据库信息的配置文件，一般每个应用服务器代码上都会存放。某个时候如果我想添加一个新数据库用户连接，那么对应用到的服务器上配置文件都要修改一遍，对于上百台的服务器，一一修改显然不现实，这时，我们可以把配置文件统一放到zookeeper服务器上，我们只需要更改zookeeper服务器上的配置文件，然后所有应用服务器上的zookeeper客户端监听到zookeeper服务器上的配置文件被改变了，进行实时同步就可以了。

主要的结构图如下：

【环境介绍】：为了看得清楚，我们这次引入两台机器，分别扮演服务器端和客户端

   服务器端（liunx系统）：10.126.101.153

   客户端（windows）：  10.249.9.19

   编程环境：java+eclipse+maven+cruator

一、启动zookeeper服务（10.126.101.153）

[root@test bin]# ./zkServer.sh start
JMX enabled by default
Using config: /home/mysql/darren/software/zookeeper-3.4./bin/../conf/zoo.cfg
Starting zookeeper ... STARTED

二、编写客户端代码（java）

由于ZooKeeper自带的客户端API太底层, 程序员在使用的时候需要自己处理很多事情，更为关键的是，使用过程中如果不当会产生很多问题，如：

• 初始化连接的问题: 在client与server之间握手建立连接的过程中, 如果握手失败, 执行所有的同步方法(比如create, getData等)将抛出异常
• 自动恢复(failover)的问题: 当client与一台server的连接丢失,并试图去连接另外一台server时, client将回到初始连接模式
• session过期的问题: 在极端情况下, 出现ZooKeeper session过期, 客户端需要自己去监听该状态并重新创建

为了方便我们编程和简化应用，这里使用cruator框架。关于cruator框架的一些介绍可以参考这里curator解决了zookeeper client哪些问题

使用cruator时，建议采用maven管理项目，maven可以为我们很容易的引入cruator依赖包，关于maven安装和配置参考这里。eclipse4.5版本以上一般都已经安装m2了，只需要配置即可。

1、采用eclipse创建maven项目

New->Other->Maven->Maven Project，然后一直默认next，填写Group Id，Artifact Id，Package，点击finish即可。

2、配置pom.xml文件，引入cruator依赖包

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.darren</groupId>
  <artifactId>zk_client</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>zk_client</name>
  <url>http://maven.apache.org</url>

  <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.netflix.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>1.3.0</version>
        </dependency>
        <dependency>
            <groupId>com.googlecode.json-simple</groupId>
            <artifactId>json-simple</artifactId>
            <version>1.1.1</version>
        </dependency>
        <dependency>
            <groupId>commons-daemon</groupId>
            <artifactId>commons-daemon</artifactId>
            <version>1.0.10</version>
        </dependency>
    </dependencies>
</project>

3、编写zookeeper 客户端操作代码

使用cruator编写zk客户端，一般分为以下几个步骤：

1）使用CuratorFrameworkFactory建立客户端到zookeeper服务器端的连接；

2）创建PathChildrenCache对象，表示zk路径节点及数据

3）为PathChildrenCache对象建立监听，这里需要实现PathChildrenCacheListener接口，用于处理监听事件逻辑。

代码如下：

 package com.darren.zk_client;

 import com.netflix.curator.framework.CuratorFramework;
 import com.netflix.curator.framework.CuratorFrameworkFactory;
 import com.netflix.curator.framework.recipes.cache.PathChildrenCache;
 import com.netflix.curator.framework.recipes.cache.PathChildrenCacheEvent;
 import com.netflix.curator.framework.recipes.cache.PathChildrenCacheListener;
 import com.netflix.curator.retry.ExponentialBackoffRetry;
 import com.netflix.curator.retry.RetryUntilElapsed;
 import com.netflix.curator.utils.ZKPaths;

 public class App
 {
     private static final String PATH = "/db/pools";

     @SuppressWarnings("resource")
     public static void main( String[] args ) throws Exception
     {
         CuratorFramework client = null;
         PathChildrenCache cache = null;
         try{
               //使用CuratorFrameworkFactory建立客户端到zookeeper服务器端的连接并启动
             client = CuratorFrameworkFactory.newClient("127.0.0.1:2181", new RetryUntilElapsed(3000, 1000));
             client.start();
               //创建PathChildrenCache对象，表示zk路径节点及数据
             cache = new PathChildrenCache(client,PATH,true);
               //为PathChildrenCache对象建立监听，这里需要实现PathChildrenCacheListener接口，用于处理监听事件逻辑
             cache.getListenable().addListener(new Listener());
             cache.start();
         }    catch(Exception e){

         }
         //表示该java程序一直运行，如果没有，每次java启动后就自动退出了
         while (true) {
             Thread.sleep(500);
         }
     }

   //内部类，用户实现监听接口
       private static class Listener implements PathChildrenCacheListener{

           @Override
           public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception {
               // TODO Auto-generated method stub
               switch (event.getType()){
                   case CHILD_ADDED:{
                       System.out.println("Node added: " + ZKPaths.getNodeFromPath(event.getData().getPath()));
                       break;
                   }
                   case CHILD_UPDATED:{
                       System.out.println("Node changed: " + ZKPaths.getNodeFromPath(event.getData().getPath()));
                       break;
                   }
                   case CHILD_REMOVED:{
                       System.out.println("Node removed: " + ZKPaths.getNodeFromPath(event.getData().getPath()));
                       break;
                   }
                   default:
                       System.out.println("no node changed!!!");
                       break;
               }
           }

       }

 }

运行效果：

2016-12-01 16:52:42,394 INFO  com.netflix.curator.framework.imps.CuratorFrameworkImpl - Starting
2016-12-01 16:52:42,482 INFO  org.apache.zookeeper.ZooKeeper - Client environment:zookeeper.version=3.4.5-1392090, built on 09/30/2012 17:52 GMT
2016-12-01 16:52:42,482 INFO  org.apache.zookeeper.ZooKeeper - Client environment:host.name=507B9D97E083.anjuke.net
2016-12-01 16:52:42,482 INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.version=1.7.0_79
2016-12-01 16:52:42,482 INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.vendor=Oracle Corporation
2016-12-01 16:52:42,482 INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.home=C:\Program Files\Java\jdk1.7.0_79\jre
2016-12-01 16:52:42,482 INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.class.path=E:\workdir\java\zk_client\target\classes;E:\workdir\java\repo\com\netflix\curator\curator-recipes\1.3.0\curator-recipes-1.3.0.jar;E:\workdir\java\repo\com\google\guava\guava\11.0.1\guava-11.0.1.jar;E:\workdir\java\repo\com\google\code\findbugs\jsr305\1.3.9\jsr305-1.3.9.jar;E:\workdir\java\repo\com\netflix\curator\curator-framework\1.3.0\curator-framework-1.3.0.jar;E:\workdir\java\repo\com\netflix\curator\curator-client\1.3.0\curator-client-1.3.0.jar;E:\workdir\java\repo\org\apache\zookeeper\zookeeper\3.4.5\zookeeper-3.4.5.jar;E:\workdir\java\repo\org\slf4j\slf4j-api\1.6.1\slf4j-api-1.6.1.jar;E:\workdir\java\repo\org\slf4j\slf4j-log4j12\1.6.1\slf4j-log4j12-1.6.1.jar;E:\workdir\java\repo\log4j\log4j\1.2.15\log4j-1.2.15.jar;E:\workdir\java\repo\javax\mail\mail\1.4\mail-1.4.jar;E:\workdir\java\repo\javax\activation\activation\1.1\activation-1.1.jar;E:\workdir\java\repo\jline\jline\0.9.94\jline-0.9.94.jar;E:\workdir\java\repo\org\jboss\netty\netty\3.2.2.Final\netty-3.2.2.Final.jar;E:\workdir\java\repo\com\googlecode\json-simple\json-simple\1.1.1\json-simple-1.1.1.jar;E:\workdir\java\repo\commons-daemon\commons-daemon\1.0.10\commons-daemon-1.0.10.jar
2016-12-01 16:52:42,483 INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.library.path=C:\Program Files\Java\jdk1.7.0_79\bin;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:/Program Files/Java/jdk1.7.0_79/bin/../jre/bin/server;C:/Program Files/Java/jdk1.7.0_79/bin/../jre/bin;C:/Program Files/Java/jdk1.7.0_79/bin/../jre/lib/amd64;C:\Program Files\Java\jdk1.7.0_79\bin;C:\Program Files\Java\jdk1.7.0_79\jre\bin;C:\Perl64\site\bin;C:\Perl64\bin;C:\Python27\;C:\Python27\Scripts;C:\Program Files (x86)\Intel\iCLS Client\;C:\Program Files\Intel\iCLS Client\;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files (x86)\MIT\Kerberos\bin;C:\CygwinPortable\App\Cygwin\bin;C:\Program Files\TortoiseGit\bin;C:\Program Files\Git\cmd;D:\Program files\apache-maven-3.3.9\bin;D:\Program files\eclipse;;.
2016-12-01 16:52:42,483 INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.io.tmpdir=C:\Users\HAILIA~1\AppData\Local\Temp\
2016-12-01 16:52:42,483 INFO  org.apache.zookeeper.ZooKeeper - Client environment:java.compiler=<NA>
2016-12-01 16:52:42,483 INFO  org.apache.zookeeper.ZooKeeper - Client environment:os.name=Windows 7
2016-12-01 16:52:42,484 INFO  org.apache.zookeeper.ZooKeeper - Client environment:os.arch=amd64
2016-12-01 16:52:42,484 INFO  org.apache.zookeeper.ZooKeeper - Client environment:os.version=6.1
2016-12-01 16:52:42,484 INFO  org.apache.zookeeper.ZooKeeper - Client environment:user.name=hailiangzhao
2016-12-01 16:52:42,484 INFO  org.apache.zookeeper.ZooKeeper - Client environment:user.home=C:\Users\hailiangzhao
2016-12-01 16:52:42,484 INFO  org.apache.zookeeper.ZooKeeper - Client environment:user.dir=E:\workdir\java\zk_client
2016-12-01 16:52:42,486 INFO  org.apache.zookeeper.ZooKeeper - Initiating client connection, connectString=10.126.101.153:2181 sessionTimeout=60000 watcher=com.netflix.curator.ConnectionState@271816d1
2016-12-01 16:52:42,718 INFO  org.apache.zookeeper.ClientCnxn - Opening socket connection to server tjtx-101-153.58os.org/10.126.101.153:2181. Will not attempt to authenticate using SASL (unknown error)
2016-12-01 16:52:42,752 INFO  org.apache.zookeeper.ClientCnxn - Socket connection established to tjtx-101-153.58os.org/10.126.101.153:2181, initiating session
2016-12-01 16:52:42,796 INFO  org.apache.zookeeper.ClientCnxn - Session establishment complete on server tjtx-101-153.58os.org/10.126.101.153:2181, sessionid = 0x158b95fadec0001, negotiated timeout = 40000
2016-12-01 16:52:42,801 INFO  com.netflix.curator.framework.state.ConnectionStateManager - State change: CONNECTED
Node added: darren.php

上面的控制台信息表示client已经与10.126.101.153:2181 zookeeper服务端建立了连接，并且对服务器上的/db/pools节点进行了监控，只要这下面的数据有任何变化，都会输出变化的node和内容。

这时，我们可以在服务器端进行如下操作：

[zk: 10.126.101.153:(CONNECTED) ] create /db/pools/darren1.php "darren1.php"
Created /db/pools/darren1.php
[zk: 10.126.101.153:(CONNECTED) ] set  /db/pools/darren1.php "xxxxxx"
cZxid = 0x7
ctime = Thu Dec  :: CST
mZxid = 0x8
mtime = Thu Dec  :: CST
pZxid = 0x7
cversion =
dataVersion =
aclVersion =
ephemeralOwner = 0x0
dataLength =
numChildren =
[zk: 10.126.101.153:(CONNECTED) ] 

这时客户端控制台追加输出，表示已经监控到了darren1.php内容改变：

Node added: darren1.php
Node changed: darren1.php

okay，使用cruator框架编写zk客户端是不是很容易呢。

当然，这个小例子很简单，还没有进行配置文件的同步，我们可以对以上程序进行如下几个改进即可实现：

1、在处理监听事件的内部类里，我们可以对变化的节点内容写入本地文件中，实现了文件同步。

2、使用daemon接口，把该java程序封装成windows或者linux服务，永久运行，保证实时同步文件。

【遇到的错误：】

【Multiple markers at this line @Override的解决方法】http://blog.csdn.net/mazhaojuan/article/details/28931375
  【maven编译时出现读取XXX时出错invalid LOC header (bad signature)】http://blog.csdn.net/woshixuye/article/details/14669929
  【log4j:WARN No appenders could be found for logger】http://www.cnblogs.com/jbelial/archive/2012/06/05/2536814.html

【moven参考资料】

【maven安装配置】http://jingyan.baidu.com/article/1709ad808ad49f4634c4f00d.html

【maven profile配置】http://elim.iteye.com/blog/1900568
  【maven处理资源文件】http://www.cnblogs.com/now-fighting/p/4888343.html
  【maven pom.xml配置说明】http://www.cnblogs.com/qq78292959/p/3711501.html

【java参考资料】

【java api官方文档】http://docs.oracle.com/javase/7/docs/api/                    
  【java程序以服务方式运行】http://blog.csdn.net/jason5186/article/details/9146167

【cruator参考资料】

【cruator简介】http://macrochen.iteye.com/blog/1366136/
  【cruator java api】http://curator.apache.org/apidocs/index.html
  【zookeeper客户端编程API】http://zookeeper.apache.org/doc/r3.4.6/javaExample.html
  【cruator 案例】http://blog.sina.com.cn/s/blog_616e189f01018axz.html