Zookeeper和Curator-Framework实践系列之： 配置管理

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！

环境，框架，工具

1. Zookeeper集群
2. Zookeeper API
3. Curator-Framework
4. Spring-MVC
5. Logback
6. Maven + IDEA

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;@Controllerpublic 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 = 0DEBUG_INT = 10INFO_INT = 20WARN_INT = 30ERROR_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。