前言
应用项目中都会有一些参数，一般的做法通常可以选择将其存储在本地配置文件或者内存变量中；对于集群机器规模不大、配置变更不是特别频繁的情况下，这两种方式都能很好的解决；但是一旦集群机器规模变大，且配置信息越来越频繁，依靠这两种方式就越来越困难；我们希望能够快速的做到全局参数的变更，因此需要一种参数的集中式管理，下面利用Zookeeper的一些特性来实现简单的参数管理。

准备

jdk:1.7.0_80 zookeeper:3.4.3 curator:2.6.0 spring:3.1.2

Maven引入

<dependency>     <groupId>org.springframework</groupId>     <artifactId>spring-core</artifactId>     <version>3.1.2.RELEASE</version> </dependency> <dependency>     <groupId>org.springframework</groupId>     <artifactId>spring-context</artifactId>     <version>3.1.2.RELEASE</version> </dependency> <dependency>     <groupId>org.springframework</groupId>     <artifactId>spring-beans</artifactId>     <version>3.1.2.RELEASE</version> </dependency> <dependency>     <groupId>org.apache.zookeeper</groupId>     <artifactId>zookeeper</artifactId>     <version>3.4.3</version>     <exclusions>         <exclusion>             <groupId>com.sun.jmx</groupId>             <artifactId>jmxri</artifactId>         </exclusion>         <exclusion>             <groupId>com.sun.jdmk</groupId>             <artifactId>jmxtools</artifactId>         </exclusion>         <exclusion>             <groupId>javax.jms</groupId>             <artifactId>jms</artifactId>         </exclusion>     </exclusions> </dependency> <dependency>     <groupId>org.apache.curator</groupId>     <artifactId>curator-framework</artifactId>     <version>2.6.0</version> </dependency> <dependency>     <groupId>org.apache.curator</groupId>     <artifactId>curator-recipes</artifactId>     <version>2.6.0</version> </dependency>

目标
1.可以同时配置监听多个节点如/app1,/app2；
2.希望只需要配置如/app1，就能够监听其子节点如/app1/modual1以及子节点的子节点如/app1/modual1/xxx/…；
3.服务器启动能获取当前指定父节点下的所有子节点数据；
4.在添加节点或者在更新节点数据的时候能够动态通知，这样代码中就能够实时获取最新的数据；
5.spring配置中可以从Zookeeper中读取参数进行初始化。

实现
提供ZKWatcher类主要用来和Zookeeper建立连接，监听节点，初始化节点数据，更新节点数据，存储节点数据等

1.同时配置监听多个节点
提供一个字符串数组给用户用来添加需要监听的节点：

private String[] keyPatterns;

2.能够监听其子节点以及子节点的子节点
使用递归的方式用来获取指定监听节点的子节点：

private List<String> listChildren(String path) throws Exception {     List<String> pathList = new ArrayList<String>();     pathList.add(path);     List<String> list = client.getChildren().forPath(path);     if (list != null && list.size() > 0) {         for (String cPath : list) {             String temp = "";             if ("/".equals(path)) {                 temp = path + cPath;             } else {                 temp = path + "/" + cPath;             }             pathList.addAll(listChildren(temp));         }     }     return pathList; }

3.服务器启动初始化节点数据
上面已经递归获取了所有的节点，所有可以遍历获取所有节点数据，并且存储在Map中：

private Map<String, String> keyValueMap = new ConcurrentHashMap<String, String>();   if (pathList != null && pathList.size() > 0) {     for (String path : pathList) {         keyValueMap.put(path, readPath(path));         watcherPath(path);     } }   private String readPath(String path) throws Exception {     byte[] buffer = client.getData().forPath(path);     String value = new String(buffer);     logger.info("readPath:path = " + path + ",value = " + value);     return value; }

4.监听节点数据的变更
使用PathChildrenCache用来监听子节点的CHILD_ADDED，CHILD_UPDATED，CHILD_REMOVED事件：

private void watcherPath(String path) {     PathChildrenCache cache = null;     try {         cache = new PathChildrenCache(client, path, true);         cache.start(StartMode.POST_INITIALIZED_EVENT);         cache.getListenable().addListener(new PathChildrenCacheListener() {               @Override             public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception {                 switch (event.getType()) {                 case CHILD_ADDED:                     logger.info("CHILD_ADDED," + event.getData().getPath());                     watcherPath(event.getData().getPath());                     keyValueMap.put(event.getData().getPath(), new String(event.getData().getData()));                     break;                 case CHILD_UPDATED:                     logger.info("CHILD_UPDATED," + event.getData().getPath());                     keyValueMap.put(event.getData().getPath(), new String(event.getData().getData()));                     break;                 case CHILD_REMOVED:                     logger.info("CHILD_REMOVED," + event.getData().getPath());                     break;                 default:                     break;                 }             }         });     } catch (Exception e) {         if (cache != null) {             try {                 cache.close();             } catch (IOException e1) {             }         }         logger.error("watch path error", e);     } }

5.spring配置中可以从Zookeeper中读取参数进行初始化
实现自定义的PropertyPlaceholderConfigurer类ZKPropPlaceholderConfigurer：

public class ZKPropPlaceholderConfigurer extends PropertyPlaceholderConfigurer {       private ZKWatcher zkwatcher;       @Override     protected Properties mergeProperties() throws IOException {         return loadPropFromZK(super.mergeProperties());     }       /**      * 从zk中加载配置的常量      *       * @param result      * @return      */     private Properties loadPropFromZK(Properties result) {         zkwatcher.watcherKeys();         zkwatcher.fillProperties(result);         return result;     }     ...... }

通过以上的处理，可以使用如下简单的配置来达到目标：

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans"     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"     xmlns:tx="http://www.springframework.org/schema/tx"     xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd         http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd         http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">       <bean id="zkwatcher" class="zh.maven.DynamicConf.ZKWatcher">         <property name="keyPatterns" value="/a2,/a3/m1" />     </bean>       <bean id="propertyConfigurer" class="zh.maven.DynamicConf.ZKPropPlaceholderConfigurer">         <property name="zkwatcher" ref="zkwatcher"></property>     </bean>       <bean id="person" class="zh.maven.DynamicConf.Person">         <property name="name">             <value>${/a2/m1}</value>         </property>         <property name="address">             <value>${/a3/m1/v2}</value>         </property>         <property name="company">             <value>${/a3/m1/v2/t2}</value>         </property>     </bean> </beans>

详细代码svn地址：http://code.taobao.org/svn/temp-pj/DynamicConf

测试
1.首先启动Zookeeper

zkServer.cmd

2.初始化需要使用的节点

public class Create_Node {       static String path = "/a3/m1/v2/t2";     static CuratorFramework client = CuratorFrameworkFactory.builder()             .connectString("127.0.0.1:2181").sessionTimeoutMs(5000)             .retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();       public static void main(String[] args) throws Exception {         client.start();         client.create().creatingParentsIfNeeded()                 .withMode(CreateMode.PERSISTENT)                 .forPath(path, "init".getBytes());     } }

创建需要的节点方便ZKWatcher来监听，这里根据以上的配置，分别初始化/a3/m1/v2/t2和/a2/m1/v1/t1

3.启动Main，分别验证配置文件中的初始化以及代码动态获取参数

public class Main {       public static void main(String[] args) throws Exception {         ApplicationContext context = new ClassPathXmlApplicationContext(new String[] { "spring-config.xml" });         Person person = (Person) context.getBean("person");         System.out.println(person.toString());           ZKWatcher zkwatcher = (ZKWatcher) context.getBean("zkwatcher");         while (true) {             Person p = new Person(zkwatcher.getKeyValue("/a2/m1"), zkwatcher.getKeyValue("/a3/m1/v2"),                     zkwatcher.getKeyValue("/a3/m1/v2/t2"));             System.out.println(p.toString());               Thread.sleep(1000);         }     } }

4.观察日志同时更新参数：

public class Set_Data {       static String path = "/a3/m1/v2/t2";     static CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181")             .sessionTimeoutMs(5000).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();       public static void main(String[] args) throws Exception {         client.start();         Stat stat = new Stat();         System.out.println(stat.getVersion());         System.out.println("Success set node for :" + path + ",new version:"                 + client.setData().forPath(path, "codingo_v2".getBytes()).getVersion());     } }

部分日志如下：

2017-08-05 18:04:57 - watcher path : [/a2, /a2/m1, /a2/m1/v1, /a2/m1/v1/t2, /a3/m1, /a3/m1/v2, /a3/m1/v2/t2] 2017-08-05 18:04:57 - readPath:path = /a2,value =  2017-08-05 18:04:57 - readPath:path = /a2/m1,value = zhaohui 2017-08-05 18:04:57 - readPath:path = /a2/m1/v1,value =  2017-08-05 18:04:57 - readPath:path = /a2/m1/v1/t2,value = init 2017-08-05 18:04:57 - readPath:path = /a3/m1,value =  2017-08-05 18:04:57 - readPath:path = /a3/m1/v2,value = nanjing 2017-08-05 18:04:57 - readPath:path = /a3/m1/v2/t2,value = codingo_v10 2017-08-05 18:04:57 - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@182f4aea: defining beans [zkwatcher,propertyConfigurer,person]; root of factory hierarchy name = zhaohui,address = nanjing,company = codingo_v10 name = zhaohui,address = nanjing,company = codingo_v10 2017-08-05 18:04:57 - CHILD_ADDED,/a2/m1 2017-08-05 18:04:57 - CHILD_ADDED,/a3/m1/v2 2017-08-05 18:04:57 - CHILD_ADDED,/a2/m1/v1 2017-08-05 18:04:57 - CHILD_ADDED,/a2/m1/v1/t2 2017-08-05 18:04:57 - CHILD_ADDED,/a3/m1/v2/t2 name = zhaohui,address = nanjing,company = codingo_v10 name = zhaohui,address = nanjing,company = codingo_v10 name = zhaohui,address = nanjing,company = codingo_v10 2017-08-05 18:05:04 - CHILD_UPDATED,/a3/m1/v2/t2 name = zhaohui,address = nanjing,company = codingo_v11 name = zhaohui,address = nanjing,company = codingo_v11

总结
通过Zookeeper实现了一个简单的参数化平台，当然想在生产中使用还有很多需要优化的地方，本文在于提供一个思路；当然除了Zookeeper还可以使用MQ，分布式缓存等来实现参数化平台。