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
- Zookeeper集群
- Zookeeper API
- Curator-Framework
- Spring-MVC
- Logback
- 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;
@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。