Zookeeper系列四：Zookeeper实现分布式锁、Zookeeper实现配置中心

一、Zookeeper实现分布式锁

分布式锁主要用于在分布式环境中保证数据的一致性。

包括跨进程、跨机器、跨网络导致共享资源不一致的问题。

1. 分布式锁的实现思路

说明：

这种实现会有一个缺点，即当有很多进程在等待锁的时候，在释放锁的时候会有很多进程就过来争夺锁，这种现象称为 “惊群效应”

2. 分布式锁优化后的实现思路

 

3. Zookeeper分布式锁的代码实现

准备工作：

1）安装Zookeeper，具体参考我前面的我文章Zookeeper系列一：Zookeeper介绍、Zookeeper安装配置、ZK Shell的使用

2）新建一个maven项目ZK-Demo,然后在pom.xml里面引入相关的依赖

        <dependency><groupId>com.101tec</groupId><artifactId>zkclient</artifactId><version>0.10</version></dependency>

3.1 Zookeeper分布式锁的核心代码实现

实现逻辑参考“2. 分布式锁优化后的实现思路”中的流程图

package com.study.demo.lock;import java.util.Collections;
import java.util.List;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;import org.I0Itec.zkclient.IZkDataListener;
import org.I0Itec.zkclient.ZkClient;
import org.I0Itec.zkclient.serialize.SerializableSerializer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;/**
* 
* @Description: Zookeeper分布式锁的核心代码实现
* @author leeSmall
* @date 2018年9月4日
*
*/
public class DistributedLock implements Lock {private static Logger logger = LoggerFactory.getLogger(DistributedLock.class);private static final String ZOOKEEPER_IP_PORT = "192.168.152.130:2181";private static final String LOCK_PATH = "/LOCK";private ZkClient client = new ZkClient(ZOOKEEPER_IP_PORT, 4000, 4000, new SerializableSerializer());private CountDownLatch cdl;private String beforePath;// 当前请求的节点前一个节点private String currentPath;// 当前请求的节点// 判断有没有LOCK目录，没有则创建public DistributedLock() {if (!this.client.exists(LOCK_PATH)) {this.client.createPersistent(LOCK_PATH);}}public void lock() {//尝试去获取分布式锁失败if (!tryLock()) {//对次小节点进行监听
            waitForLock();lock();} else {logger.info(Thread.currentThread().getName() + " 获得分布式锁！");}}public boolean tryLock() {// 如果currentPath为空则为第一次尝试加锁，第一次加锁赋值currentPathif (currentPath == null || currentPath.length() <= 0) {// 创建一个临时顺序节点currentPath = this.client.createEphemeralSequential(LOCK_PATH + '/', "lock");System.out.println("---------------------------->" + currentPath);}// 获取所有临时节点并排序，临时节点名称为自增长的字符串如：0000000400List<String> childrens = this.client.getChildren(LOCK_PATH);//由小到大排序所有子节点
        Collections.sort(childrens);//判断创建的子节点/LOCK/Node-n是否最小,即currentPath,如果当前节点等于childrens中的最小的一个就占用锁if (currentPath.equals(LOCK_PATH + '/' + childrens.get(0))) {return true;} //找出比创建的临时顺序节子节点/LOCK/Node-n次小的节点,并赋值给beforePathelse {int wz = Collections.binarySearch(childrens, currentPath.substring(6));beforePath = LOCK_PATH + '/' + childrens.get(wz - 1);}return false;}//等待锁,对次小节点进行监听private void waitForLock() {IZkDataListener listener = new IZkDataListener() {public void handleDataDeleted(String dataPath) throws Exception {logger.info(Thread.currentThread().getName() + ":捕获到DataDelete事件！---------------------------");if (cdl != null) {cdl.countDown();}}public void handleDataChange(String dataPath, Object data) throws Exception {}};// 对次小节点进行监听,即beforePath-给排在前面的的节点增加数据删除的watcherthis.client.subscribeDataChanges(beforePath, listener);if (this.client.exists(beforePath)) {cdl = new CountDownLatch(1);try {cdl.await();} catch (InterruptedException e) {e.printStackTrace();}}this.client.unsubscribeDataChanges(beforePath, listener);}//完成业务逻辑以后释放锁public void unlock() {// 删除当前临时节点
        client.delete(currentPath);}// ==========================================public void lockInterruptibly() throws InterruptedException {}public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {return false;}public Condition newCondition() {return null;}
}

 3.2 在业务里面使用分布式锁

package com.study.demo.lock;import java.util.concurrent.CountDownLatch;
import java.util.concurrent.locks.Lock;import org.slf4j.Logger;
import org.slf4j.LoggerFactory;/**
* 
* @Description: 在业务里面使用分布式锁
* @author leeSmall
* @date 2018年9月4日
*
*/
public class OrderServiceImpl implements Runnable {private static OrderCodeGenerator ong = new OrderCodeGenerator();private Logger logger = LoggerFactory.getLogger(OrderServiceImpl.class);// 同时并发的线程数private static final int NUM = 10;// 按照线程数初始化倒计数器,倒计数器private static CountDownLatch cdl = new CountDownLatch(NUM);private Lock lock = new DistributedLock();// 创建订单接口public void createOrder() {String orderCode = null;//准备获取锁
        lock.lock();try {// 获取订单编号orderCode = ong.getOrderCode();} catch (Exception e) {// TODO: handle exception} finally {//完成业务逻辑以后释放锁
            lock.unlock();}// ……业务代码
logger.info("insert into DB使用id：=======================>" + orderCode);}public void run() {try {// 等待其他线程初始化
            cdl.await();} catch (InterruptedException e) {// TODO Auto-generated catch block
            e.printStackTrace();}// 创建订单
        createOrder();}public static void main(String[] args) {for (int i = 1; i <= NUM; i++) {// 按照线程数迭代实例化线程new Thread(new OrderServiceImpl()).start();// 创建一个线程，倒计数器减1
            cdl.countDown();}}
}

工具类：

package com.study.demo.lock;import java.text.SimpleDateFormat;
import java.util.Date;public class OrderCodeGenerator {// 自增长序列private static int i = 0;// 按照“年-月-日-小时-分钟-秒-自增长序列”的规则生成订单编号public String getOrderCode() {Date now = new Date();SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmss");return sdf.format(now) + ++i;}}

二、Zookeeper实现配置中心

 1. 首先在zookeeper里面创建一个Jdbc的节点，在下面分别创建4个子节点/Jdbc/url、/Jdbc/uname、/Jdbc/password、/Jdbc/driver

create /Jdbc ''
create /Jdbc/url jdbc.mysql://192.168.152.1/dbspread 
create /Jdbc/uname root
create /Jdbc/password 123456
create /Jdbc/driver com.mysql.jdbc.Driver

注意：/Jdbc/url这个节点的值是错的 

 

 

 2. 新建一个zkdemo的maven的web项目

项目结构如下：

2.1 在pom.xml文件里面引入下面依赖：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.study.demo</groupId><artifactId>zkdemo</artifactId><packaging>war</packaging><version>0.0.1-SNAPSHOT</version><name>zkdemo Maven Webapp</name><url>http://maven.apache.org</url><properties><spring.version>4.3.8.RELEASE</spring.version></properties><dependencies><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>3.8.1</version><scope>test</scope></dependency><dependency><groupId>org.apache.zookeeper</groupId><artifactId>zookeeper</artifactId><version>3.4.10</version></dependency><dependency><groupId>com.101tec</groupId><artifactId>zkclient</artifactId><version>0.10</version></dependency><dependency><groupId>org.apache.curator</groupId><artifactId>curator-framework</artifactId><version>4.0.0</version></dependency><dependency><groupId>org.apache.curator</groupId><artifactId>curator-recipes</artifactId><version>4.0.0</version></dependency><dependency><groupId>javax.servlet</groupId><artifactId>javax.servlet-api</artifactId><version>3.1.0</version></dependency><dependency><groupId>org.apache.tomcat</groupId><artifactId>tomcat-catalina</artifactId><version>7.0.39</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-core</artifactId><version>${spring.version}</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-beans</artifactId><version>${spring.version}</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-jdbc</artifactId><version>${spring.version}</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>${spring.version}</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-web</artifactId><version>${spring.version}</version></dependency><dependency><groupId>org.springframework</groupId><artifactId>spring-webmvc</artifactId><version>${spring.version}</version></dependency><dependency><groupId>com.zaxxer</groupId><artifactId>HikariCP</artifactId><version>2.7.1</version></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>5.1.41</version></dependency><dependency><groupId>org.slf4j</groupId><artifactId>slf4j-api</artifactId><version>1.7.25</version></dependency><dependency><groupId>org.slf4j</groupId><artifactId>jcl-over-slf4j</artifactId><version>1.7.25</version></dependency><dependency><groupId>log4j</groupId><artifactId>log4j</artifactId><version>1.2.17</version></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-core</artifactId><version>2.9.1</version></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.9.1</version></dependency><dependency><groupId>javax.servlet</groupId><artifactId>jstl</artifactId><version>1.2</version></dependency></dependencies><build><finalName>zkdemo</finalName></build>
</project>

2.2 新建一个zookeeper配置中心类,从zookeeper动态获取数据库配置

package com.study.demo.config;import java.util.List;
import java.util.Properties;import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.cache.TreeCache;
import org.apache.curator.framework.recipes.cache.TreeCacheEvent;
import org.apache.curator.framework.recipes.cache.TreeCacheListener;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.WebApplicationContext;import com.zaxxer.hikari.HikariDataSource;/**
* 
* @Description: zookeeper配置中心类,从zookeeper动态获取数据库配置
* @author leeSmall
* @date 2018年9月10日
*
*/
public class ZookeeperConfigurerCentral {//curator客户端private CuratorFramework zkClient;//curator事件监听private TreeCache treeCache;//zookeeper的ip和端口private String zkServers;//zookeeper上的/Jdbc路径private String zkPath;//超时设置private int sessionTimeout;//读取zookeeper上的数据库配置文件放到这里private Properties props;public ZookeeperConfigurerCentral(String zkServers, String zkPath, int sessionTimeout) {this.zkServers = zkServers;this.zkPath = zkPath;this.sessionTimeout = sessionTimeout;this.props = new Properties();//初始化curator客户端
        initZkClient();//从zookeeper的Jdbc节点下获取数据库配置存入props
        getConfigData();//对zookeeper上的数据库配置文件所在节点进行监听，如果有改变就动态刷新props
        addZkListener();}//初始化curator客户端private void initZkClient() {zkClient = CuratorFrameworkFactory.builder().connectString(zkServers).sessionTimeoutMs(sessionTimeout).retryPolicy(new ExponentialBackoffRetry(1000, 3)).build();zkClient.start();}//从zookeeper的Jdbc节点下获取数据库配置存入propsprivate void getConfigData() {try {List<String> list = zkClient.getChildren().forPath(zkPath);for (String key : list) {String value = new String(zkClient.getData().forPath(zkPath + "/" + key));if (value != null && value.length() > 0) {props.put(key, value);}}} catch (Exception e) {e.printStackTrace();}}//对zookeeper上的数据库配置文件所在节点进行监听，如果有改变就动态刷新propsprivate void addZkListener() {TreeCacheListener listener = new TreeCacheListener() {public void childEvent(CuratorFramework client, TreeCacheEvent event) throws Exception {if (event.getType() == TreeCacheEvent.Type.NODE_UPDATED) {getConfigData();WebApplicationContext ctx = ContextLoader.getCurrentWebApplicationContext();HikariDataSource dataSource = (HikariDataSource) ctx.getBean("dataSource");System.out.println("================"+props.getProperty("url"));dataSource.setJdbcUrl(props.getProperty("url"));dataSource.setUsername(props.getProperty("uname"));dataSource.setPassword(props.getProperty("password "));dataSource.setDriverClassName(props.getProperty("driver "));}}};treeCache = new TreeCache(zkClient, zkPath);try {treeCache.start();treeCache.getListenable().addListener(listener);} catch (Exception e) {e.printStackTrace();}}public Properties getProps() {return props;}public void setZkServers(String zkServers) {this.zkServers = zkServers;}public void setZkPath(String zkPath) {this.zkPath = zkPath;}public void setSessionTimeout(int sessionTimeout) {this.sessionTimeout = sessionTimeout;}
}

2.3 新建一个加载props里面的数据库配置的类

package com.study.demo.config;import java.util.Properties;import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.beans.factory.config.PropertyPlaceholderConfigurer;/**
* 
* @Description: 加载props里面的数据库配置,这个类等价于以前在xml文件里面的配置：
* <context:property-placeholder location="classpath:config/jdbc_conf.properties"/>
* @author leeSmall
* @date 2018年9月10日
*
*/
public class ZookeeperPlaceholderConfigurer extends PropertyPlaceholderConfigurer {private ZookeeperConfigurerCentral zkConfigurerCentral;@Overrideprotected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)throws BeansException {System.out.println(zkConfigurerCentral.getProps());super.processProperties(beanFactoryToProcess, zkConfigurerCentral.getProps());}public void setzkConfigurerCentral(ZookeeperConfigurerCentral zkConfigurerCentral) {this.zkConfigurerCentral = zkConfigurerCentral;}
}

2.4 在/zkdemo/src/main/webapp/WEB-INF/config/applicationContext.xml配置2.2和2.3新建的两个主类

<?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:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd  http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"><context:annotation-config /><context:component-scan base-package="com.study.demo" /><!--通过构造函数注入zkServers、sessionTimeout、zkPath从zookeeper动态获取数据库配置  --><bean id="zkConfigurerCentral" class="com.study.demo.config.ZookeeperConfigurerCentral"><constructor-arg name="zkServers" value="192.168.152.130:2181" /><constructor-arg name="sessionTimeout" value="1000" /><constructor-arg name="zkPath" value="/Jdbc" /></bean><!--这个类等价于以前在xml文件里面的配置：<context:property-placeholder location="classpath:config/jdbc_conf.properties"/>  加载props里面的数据库配置--><bean id="zkPlaceholderConfigurer" class="com.study.demo.config.ZookeeperPlaceholderConfigurer"><property name="zkConfigurerCentral" ref="zkConfigurerCentral" /><property name="ignoreUnresolvablePlaceholders" value="true" /><property name="order" value="1" /></bean><bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate"><property name="dataSource"><ref bean="dataSource" /></property></bean><bean id="dataSource" class="com.zaxxer.hikari.HikariDataSource"destroy-method="shutdown"><property name="driverClassName" value="${driver}" /><property name="jdbcUrl" value="${url}" /><property name="username" value="${uname}" /><property name="password" value="${password}" /><!-- 连接只读数据库时配置为true， 保证安全 --><property name="readOnly" value="false" /><!-- 等待连接池分配连接的最大时长（毫秒），超过这个时长还没可用的连接则发生SQLException， 缺省:30秒 --><property name="connectionTimeout" value="30000" /><!-- 一个连接idle状态的最大时长（毫秒），超时则被释放（retired），缺省:10分钟 --><property name="idleTimeout" value="600000" /><!-- 一个连接的生命时长（毫秒），超时而且没被使用则被释放（retired），缺省:30分钟，建议设置比数据库超时时长少30秒，参考MySQL wait_timeout参数（show variables like '%timeout%';） --><property name="maxLifetime" value="1800000" /><!-- 连接池中允许的最大连接数。缺省值：10；推荐的公式：((core_count * 2) + effective_spindle_count) --><property name="maximumPoolSize" value="15" /></bean>
</beans>

2.5 在com.study.demo.controller新建测试类

测试类1：

package com.study.demo.controller;import java.io.Serializable;public class OrderModel implements Serializable {private static final long serialVersionUID = 1L;private int orderId;private int brandId;public int getOrderId() {return orderId;}public void setOrderId(int orderId) {this.orderId = orderId;}public int getBrandId() {return brandId;}public void setBrandId(int brandId) {this.brandId = brandId;}}

测试类2：

package com.study.demo.controller;import java.sql.ResultSet;
import java.sql.SQLException;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.jdbc.core.RowMapper;
import org.springframework.stereotype.Repository;@Repository
public class OrderDao {@Autowiredprivate JdbcTemplate jdbcTemplate;public OrderModel findById() {String sql = "select * from tbl_order where order_id = 1";return jdbcTemplate.queryForObject(sql, new RowMapper<OrderModel>() {public OrderModel mapRow(ResultSet rs, int rowNum) throws SQLException {OrderModel payment = new OrderModel();payment.setOrderId(rs.getInt("order_id"));payment.setBrandId(rs.getInt("brand_id"));return payment;}});}
}

测试类3：

package com.study.demo.controller;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;@Service
public class OrderService {@Autowiredprivate OrderDao dao;public OrderModel getById() {return dao.findById();}
}

测试类4：

package com.study.demo.controller;import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;@Controller
public class OrderController {@Autowiredprivate OrderService service;@ResponseBody@RequestMapping(value = "/test", method = RequestMethod.GET)public String test() {OrderModel p = service.getById();return p.getBrandId() + "";}
}

2.6 其他附加配置和数据库脚本

/zkdemo/src/main/webapp/WEB-INF/config/log4j.properties

log4j.rootLogger=INFO,console
log4j.logger.org.apache.zookeeper=DEBUG
log4j.logger.org.apache.curator=DEBUG
log4j.logger.java.lang.Exception=INFOlog4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=%d{MM-dd HH:mm:ss.SSS} [%c:%p] %m%n

/zkdemo/src/main/webapp/WEB-INF/config/spring-mvc.xml

<?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:context="http://www.springframework.org/schema/context"xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:aop="http://www.springframework.org/schema/aop"xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsdhttp://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsdhttp://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd"><mvc:default-servlet-handler /><mvc:annotation-drivencontent-negotiation-manager="contentNegotiationManager" /><context:component-scan base-package="com.study.demo"><context:include-filter type="annotation"expression="org.springframework.stereotype.Controller" /><context:exclude-filter type="annotation"expression="org.springframework.stereotype.Service" /></context:component-scan><bean id="stringHttpMessageConverter"class="org.springframework.http.converter.StringHttpMessageConverter"><property name="supportedMediaTypes"><list><bean class="org.springframework.http.MediaType"><constructor-arg index="0" value="text" /><constructor-arg index="1" value="plain" /><constructor-arg index="2" value="UTF-8" /></bean></list></property></bean><bean id="mappingJacksonHttpMessageConverter"class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter" /><beanclass="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter"><property name="messageConverters"><list><ref bean="stringHttpMessageConverter" /><ref bean="mappingJacksonHttpMessageConverter" /></list></property></bean><bean id="contentNegotiationManager"class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean"><property name="mediaTypes"><map><entry key="html" value="text/html" /><entry key="pdf" value="application/pdf" /><entry key="xsl" value="application/vnd.ms-excel" /><entry key="xml" value="application/xml" /><entry key="json" value="application/json" /></map></property><property name="defaultContentType" value="text/html" /></bean><bean id="viewResolver"class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver"><property name="order" value="0" /><property name="contentNegotiationManager" ref="contentNegotiationManager" /><property name="viewResolvers"><list><bean class="org.springframework.web.servlet.view.BeanNameViewResolver" /><beanclass="org.springframework.web.servlet.view.InternalResourceViewResolver"><property name="viewClass"value="org.springframework.web.servlet.view.JstlView" /><property name="prefix" value="/WEB-INF/pages/" /><property name="suffix" value=".jsp"></property></bean></list></property><property name="defaultViews"><list><beanclass="org.springframework.web.servlet.view.json.MappingJackson2JsonView"><property name="extractValueFromSingleKeyModel" value="true" /></bean></list></property></bean>
</beans>

/zkdemo/src/main/webapp/WEB-INF/web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.5"xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"><display-name>zkdemo</display-name><description>Zookeeper Demo Application</description><!--============================================================== --><!-- Context parameters definition --><!--============================================================== --><context-param><param-name>webAppRootKey</param-name><param-value>zkdemo.root</param-value></context-param><context-param><param-name>log4jConfigLocation</param-name><param-value>/WEB-INF/config/log4j.properties</param-value></context-param><context-param><param-name>log4jRefreshInterval</param-name><param-value>60000</param-value></context-param><context-param><param-name>contextConfigLocation</param-name><param-value>/WEB-INF/config/applicationContext.xml</param-value></context-param><servlet><servlet-name>spring</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>/WEB-INF/config/spring-mvc.xml</param-value></init-param><load-on-startup>1</load-on-startup></servlet><servlet-mapping><servlet-name>spring</servlet-name><url-pattern>/</url-pattern></servlet-mapping><!--============================================================== --><!-- Listener definition --><!--============================================================== --><listener><listener-class>org.springframework.web.util.Log4jConfigListener</listener-class></listener><listener><listener-class>org.springframework.web.context.ContextLoaderListener</listener-class></listener><!--============================================================== --><!-- Filter definition --><!--============================================================== --><filter><filter-name>characterEncodingFilter</filter-name><filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class><init-param><param-name>encoding</param-name><param-value>UTF-8</param-value></init-param><init-param><param-name>forceEncoding</param-name><param-value>true</param-value></init-param></filter><filter-mapping><filter-name>characterEncodingFilter</filter-name><url-pattern>/*</url-pattern></filter-mapping><!--============================================================== --><!-- Web Session definition --><!--============================================================== --><session-config><session-timeout>20</session-timeout></session-config><!--============================================================== --><!-- Redirect page definition --><!--============================================================== --><error-page><error-code>403</error-code><location>/403.jsp</location></error-page><error-page><error-code>404</error-code><location>/404.jsp</location></error-page><error-page><error-code>500</error-code><location>/500.jsp</location></error-page><!--============================================================== --><!-- First page definition --><!--============================================================== --><welcome-file-list><welcome-file>index.htm</welcome-file><welcome-file>index.jsp</welcome-file></welcome-file-list></web-app>

数据库脚本：

CREATE TABLE `tbl_order` (`order_id` int(11) NOT NULL AUTO_INCREMENT COMMENT '订单id',`brand_id` int(11) DEFAULT NULL COMMENT '品牌id',PRIMARY KEY (`order_id`)
) ENGINE=MyISAM AUTO_INCREMENT=2 DEFAULT CHARSET=utf8 COMMENT='订单表';INSERT INTO tbl_order VALUES('1','1')

 2.7 启动项目在浏览器输入地址http://localhost:8080/zkdemo/test查看效果

 

可以看到报错了，这是因为我们之前设置了错误的url

create /Jdbc/url jdbc.mysql://192.168.152.1/dbspread 

修改url为正确的 

set /Jdbc/url jdbc:mysql://192.168.152.1:3306/dbspread

 

 再次输入地址访问查看效果：

http://localhost:8080/zkdemo/test

可以看到在没有重启服务的情况下，可以正常访问获取到值了，这是因为zookeeper的数据库的配置动态刷新到服务了！