最近在工作中，为了完善公司集群服务的架构，提高可用性，降低运维成本，因此开始学习ZooKeeper。
至于什么是ZooKeeper？它能做什么？如何安装ZooKeeper？我就不一一介绍了，类似这些资料网上到处都是。我主要是把在开发过程中，以及个人对ZooKeeper的一些了解记录下来，大家如果遇到类似场景时，希望我的文章能够给你提供一些思路。
我使用的ZooKeeper（以下简称：ZK）客户端是Curator Framework，是Apache的项目，它主要的功能是为ZK的客户端使用提供了高可用的封装。在Curator Framework基础上封装的curator-recipes，实现了很多经典场景。比如：集群管理（Leader选举）、共享锁、队列、Counter等等。可以总结Curator主要解决以下三类问题：
- 封装ZK Client与Server之间的连接处理；
- 提供了一套Fluent风格的操作API；
- 提供ZK各种应用场景的抽象封装；
本文主要完成的目标是：Spring PropertyPlaceholderConfigurer配置文件加载器集成ZooKeeper来实现远程配置读取。
配置管理（Configuration Management）。
在集群服务中，可能都会遇到一个问题：那就是当需要修改配置的时候，必须要对每个实例都进行修改，这是一个很繁琐的事情，并且易出错。当然可以使用脚本来解决，但这不是最好的解决办法。
OK，Let's go！
我们先看看项目结构
ZooKeeperPropertyPlaceholderConfigurer.java
继承org.springframework.beans.factory.config.PropertyPlaceholderConfigurer，重写processProperties(beanFactoryToProcess, props)来完成远端配置加载的实现
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package org.bigmouth.common.zookeeper.config.spring;import java.io.UnsupportedEncodingException;import java.util.Properties;import org.apache.commons.lang.StringUtils;import org.bigmouth.common.zookeeper.config.Config;import org.bigmouth.common.zookeeper.config.ZooKeeperConfig;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;public class ZooKeeperPropertyPlaceholderConfigurer extends PropertyPlaceholderConfigurer { public static final String PATH = "zoo.paths"; @Override protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props) throws BeansException { super.processProperties(beanFactoryToProcess, props); try { fillCustomProperties(props); System.out.println(props); } catch (Exception e) { // Ignore e.printStackTrace(); } } private void fillCustomProperties(Properties props) throws Exception { byte[] data = getData(props); fillProperties(props, data); } private void fillProperties(Properties props, byte[] data) throws UnsupportedEncodingException { String cfg = new String(data, "UTF-8"); if (StringUtils.isNotBlank(cfg)) { // 完整的应该还需要处理：多条配置、value中包含=、忽略#号开头 String[] cfgItem = StringUtils.split(cfg, "="); props.put(cfgItem[0], cfgItem[1]); } } private byte[] getData(Properties props) throws Exception { String path = props.getProperty(PATH); Config config = new ZooKeeperConfig(); return config.getConfig(path); }} |
Config.java
配置操作接口
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package org.bigmouth.common.zookeeper.config;public interface Config { byte[] getConfig(String path) throws Exception;} |
Startup.java
程序启动入口
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package org.bigmouth.common.zookeeper.config;import org.springframework.context.support.ClassPathXmlApplicationContext;public class Startup { public static void main(String[] args) { new ClassPathXmlApplicationContext("classpath:/config/applicationContext.xml"); }} |
ZooKeeperConfig.java
配置操作接口ZooKeeper的实现
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package org.bigmouth.common.zookeeper.config;import org.apache.curator.framework.CuratorFramework;import org.apache.zookeeper.data.Stat;public class ZooKeeperConfig implements Config { @Override public byte[] getConfig(String path) throws Exception { CuratorFramework client = ZooKeeperFactory.get(); if (!exists(client, path)) { throw new RuntimeException("Path " + path + " does not exists."); } return client.getData().forPath(path); } private boolean exists(CuratorFramework client, String path) throws Exception { Stat stat = client.checkExists().forPath(path); return !(stat == null); }} |
ZooKeeperFactory.java
管理ZooKeeper客户端连接
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package org.bigmouth.common.zookeeper.config;import org.apache.curator.RetryPolicy;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.retry.ExponentialBackoffRetry;public class ZooKeeperFactory { public static final String CONNECT_STRING = "172.16.3.42:2181,172.16.3.65:2181,172.16.3.24:2181"; public static final int MAX_RETRIES = 3; public static final int BASE_SLEEP_TIMEMS = 3000; public static final String NAME_SPACE = "cfg"; public static CuratorFramework get() { RetryPolicy retryPolicy = new ExponentialBackoffRetry(BASE_SLEEP_TIMEMS, MAX_RETRIES); CuratorFramework client = CuratorFrameworkFactory.builder() .connectString(CONNECT_STRING) .retryPolicy(retryPolicy) .namespace(NAME_SPACE) .build(); client.start(); return client; }} |
applicationContext.xml
配置加载器使用我们自己创建的ZooKeeperPropertyPlaceholderConfigurer，因为它重写了processProperties方法。这个方法里会去读取远程配置。
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<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd"><beans> <bean class="org.bigmouth.common.zookeeper.config.spring.ZooKeeperPropertyPlaceholderConfigurer"> <property name="systemPropertiesModeName" value="SYSTEM_PROPERTIES_MODE_OVERRIDE" /> <property name="ignoreResourceNotFound" value="true" /> <property name="locations"> <list> <value>classpath:application.properties</value> </list> </property> </bean> </beans> |
application.properties
项目配置文件，里面除了配置ZooKeeper服务器地址和读取的节点以外，其他所有的配置都应该保存在ZooKeeper中。
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zoo.paths=/properties |
设置ZooKeeper数据
登录ZooKeeper中为节点 /cfg/properties 添加一条配置项：
如图所示：我创建了一个节点 /cfg/properties 并设置内容为：jdbc.driver=org.postgresql.Driver
运行Startup.java
OK 了，zoo.paths是本地application.properties文件中的，jdbc.driver是远程ZooKeeper服务器中的。
项目中需要依赖的jar包
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<dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>2.4</version></dependency><dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>3.0.3.RELEASE</version></dependency><dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>3.0.3.RELEASE</version></dependency><dependency> <groupId>org.springframework</groupId> <artifactId>spring-tx</artifactId> <version>3.0.3.RELEASE</version></dependency><dependency> <groupId>org.springframework</groupId> <artifactId>spring-context-support</artifactId> <version>3.0.3.RELEASE</version></dependency><!-- ZooKeeper --><dependency> <groupId>org.apache.zookeeper</groupId> <artifactId>zookeeper</artifactId> <version>3.4.6</version></dependency><dependency> <groupId>org.apache.curator</groupId> <artifactId>curator-framework</artifactId> <version>2.4.2</version></dependency><dependency> <groupId>org.apache.curator</groupId> <artifactId>curator-recipes</artifactId> <version>2.4.2</version></dependency> |