看过Zookeeper相关文档后都知道它可以实现分布式集群的配置管理，本文以一个简单的实例来演示它是如何实现的并工作的。
情景需要，简单理解为下图：
一个web集群，需要通过zk来控制集群的日志输出级别，比如管理员需要在生产环境下查看一下DEBUG日志，他可以临时将集群的日志输出级别改为DEBUG，获取他想要的信息后还要将级别调回到INFO或者ERROR级别。
今天的主角是Curator-Framework，它的存在使得我们操作ZK变得简单有趣起来！
POM
依赖关系和jetty插件
<dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>3.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> <version>3.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>3.2.3.RELEASE</version> </dependency> <dependency> <groupId>org.apache.zookeeper</groupId> <artifactId>zookeeper</artifactId> <version>3.4.5</version> <exclusions> <exclusion> <groupId>log4j</groupId> <artifactId>log4j</artifactId> </exclusion> <exclusion> <groupId>org.slf4j</groupId> <artifactId>slf4j-log4j12</artifactId> </exclusion> </exclusions> </dependency> <dependency> <groupId>org.apache.curator</groupId> <artifactId>curator-framework</artifactId> <version>2.0.1-incubating</version> </dependency> <dependency> <groupId>org.apache.curator</groupId> <artifactId>curator-recipes</artifactId> <version>2.0.1-incubating</version> </dependency> <dependency> <groupId>ch.qos.logback</groupId> <artifactId>logback-classic</artifactId> <version>1.0.13</version> </dependency> <dependency> <version>1.7.5</version> <groupId>org.slf4j</groupId> <artifactId>slf4j-api</artifactId> </dependency> <dependency> <groupId>org.testng</groupId> <artifactId>testng</artifactId> <version>6.8.5</version> <scope>test</scope> </dependency> </dependencies> <build> <finalName>zookeeper-configuration</finalName> <plugins> <plugin> <groupId>org.mortbay.jetty</groupId> <artifactId>jetty-maven-plugin</artifactId> <version>8.1.7.v20120910</version> <configuration> <stopKey>pbase</stopKey> <stopPort>8080</stopPort> </configuration> </plugin> </plugins> </build> |
WEB.XML
这个不用解释了，地球人都知道
<web-app> <display-name>Archetype Created Web Application</display-name> <context-param> <param-name>contextConfigLocation</param-name> <param-value> classpath*:/applicationContext.xml </param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <servlet> <servlet-name>springServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>classpath*:/spring-mvc.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>springServlet</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping> </web-app> |
Spring 配置
applicationContext.xml
<context:component-scan base-package="cn.bg"> <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/> </context:component-scan> <!-- Curator的FactoryBean，Spring启动时创建Curator实例。 --> <bean id="zookeeperFactoryBean" class="cn.bg.zk.core.ZookeeperFactoryBean" lazy-init="false"> <property name="zkConnectionString" value="hadoopmaster:2181"/> <!-- 设置zookeeper的事件监听者，本例是一个logback日志级别znode监听器 --> <property name="listeners"> <list> <bean class="cn.bg.zk.configuration.LogbackLevelListener"> <constructor-arg value="/zk_test/logbacklevel"/> </bean> </list> </property> </bean> |
spring-mvc.xml
<context:component-scan base-package="cn.bg"> <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/> </context:component-scan> <mvc:annotation-driven></mvc:annotation-driven> |
Zookeeper配置管理实现相关类
ZookeeperFactoryBean.java
在Spring Context加载过程中创建Zookeeper链接对像并设置触发监听，通过Curator.
package cn.bg.zk.core; public class ZookeeperFactoryBean implements FactoryBean<CuratorFramework>, InitializingBean, DisposableBean { private Logger logger = LoggerFactory.getLogger(this.getClass()); private CuratorFramework zkClient; //设置Zookeeper启动后需要调用的监听或者，或者需要做的初始化工作。 public void setListeners(List<IZKListener> listeners) { this.listeners = listeners; } private List<IZKListener> listeners; //设置ZK链接串 public void setZkConnectionString(String zkConnectionString) { this.zkConnectionString = zkConnectionString; } private String zkConnectionString; @Override public CuratorFramework getObject() { return zkClient; } @Override public Class<?> getObjectType() { return CuratorFramework.class; } @Override public boolean isSingleton() { return true; } @Override public void destroy() throws Exception { zkClient.close(); } //创建ZK链接 @Override public void afterPropertiesSet(){ //1000 是重试间隔时间基数，3 是重试次数 RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3); zkClient = createWithOptions(zkConnectionString, retryPolicy, 2000, 10000); registerListeners(zkClient); zkClient.start(); } /** * 通过自定义参数创建 */ public CuratorFramework createWithOptions(String connectionString, RetryPolicy retryPolicy, int connectionTimeoutMs, int sessionTimeoutMs) { return CuratorFrameworkFactory.builder() .connectString(connectionString) .retryPolicy(retryPolicy) .connectionTimeoutMs(connectionTimeoutMs) .sessionTimeoutMs(sessionTimeoutMs) .build(); } //注册需要监听的监听者对像. private void registerListeners(CuratorFramework client){ client.getConnectionStateListenable().addListener(new ConnectionStateListener() { @Override public void stateChanged(CuratorFramework client, ConnectionState newState) { logger.info("CuratorFramework state changed: {}", newState); if(newState == ConnectionState.CONNECTED || newState == ConnectionState.RECONNECTED){ for(IZKListener listener : listeners){ listener.executor(client); logger.info("Listener {} executed!", listener.getClass().getName()); } } } }); client.getUnhandledErrorListenable().addListener(new UnhandledErrorListener() { @Override public void unhandledError(String message, Throwable e) { logger.info("CuratorFramework unhandledError: {}", message); } }); } } |
监听事件接口
所有需要在ZK客户端链接成功后需要做的事件，需要实现这个接口，由上面的ZookeeperFactoryBean统一调度。
package cn.bg.zk.core; import org.apache.curator.framework.CuratorFramework; public interface IZKListener { void executor(CuratorFramework client); } |
Logback监听实现
这里主要用到Curator的NodeCache类，它的主要功能是用来监听znode本身的变化，并可以获取当前值，而且会自动重复监听，简化了原生API开发的繁琐过程。
package cn.bg.zk.configuration; public class LogbackLevelListener implements IZKListener { //获取logback实例 Logger log = (Logger) LoggerFactory.getLogger(this.getClass()); private String path; //Logback日志级别ZNode public LogbackLevelListener(String path) { this.path = path; } @Override public void executor(CuratorFramework client) { //使用Curator的NodeCache来做ZNode的监听，不用我们自己实现重复监听 final NodeCache cache = new NodeCache(client, path); cache.getListenable().addListener(new NodeCacheListener() { @Override public void nodeChanged() throws Exception { byte[] data = cache.getCurrentData().getData(); //设置日志级别 if (data != null) { String level = new String(data); Logger logger = (Logger) LoggerFactory.getLogger("root"); Level newLevel = Level.fromLocationAwareLoggerInteger(Integer.parseInt(level)); logger.setLevel(newLevel); System.out.println("Setting logback new level to :" + newLevel.levelStr); } } }); try { cache.start(true); } catch (Exception e) { log.error("Start NodeCache error for path: {}, error info: {}", path, e.getMessage()); } } } |
通过WEB端查看当前日志级别
写一个controller来读取logback的日志级别
MainController.java
package cn.bg.controller; @Controller public class MainController { @RequestMapping("/") @ResponseBody public String logbackLevel() throws Exception { Logger logger = (Logger) LoggerFactory.getLogger("root"); String levelStr = logger.getLevel().levelStr; return levelStr; } } |
运行
在ZK集群端启动zkCli创建/zk_test/logbacklevel的znode，设置值为10，或20在控制台来查看logback的日志输出情况，logback日志级别数据表示如下：
TRACE_INT = 0 DEBUG_INT = 10 INFO_INT = 20 WARN_INT = 30 ERROR_INT = 40 |
到此就实现了一个简单的ZK配置管理情境，有了Curator-Framework后一切变的简单起来，我们主要精力只要解决业务相关的的需要，而ZK相关的实现由Curator来解决。
下一篇介绍Curator分布式队列实现。
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