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

Z时代
2024-01-10
分类：综合

coding

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
*
*/
publicclass DistributedLock implements Lock {
privatestatic Logger logger = LoggerFactory.getLogger(DistributedLock.class);
privatestaticfinal String ZOOKEEPER_IP_PORT = "192.168.152.130:2181";
privatestaticfinal 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);
        }
    }
publicvoid 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！");
        }
    }
publicboolean tryLock() {
// 如果currentPath为空则为第一次尝试加锁，第一次加锁赋值currentPath
if (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：0000000400
        List<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))) {
returntrue;
        } 
//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beforePath
else {
int wz = Collections.binarySearch(childrens, currentPath.substring(6));
            beforePath = LOCK_PATH + '/' + childrens.get(wz - 1);
        }
returnfalse;
    }
//等待锁,对次小节点进行监听
privatevoid waitForLock() {
        IZkDataListener listener = new IZkDataListener() {
publicvoid handleDataDeleted(String dataPath) throws Exception {
                logger.info(Thread.currentThread().getName() + ":捕获到DataDelete事件！---------------------------");
if (cdl != null) {
                    cdl.countDown();
                }
            }
publicvoid 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watcher
this.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
publicvoid unlock() {
// 删除当前临时节点
        client.delete(currentPath);
    }
// ==========================================
publicvoid lockInterruptibly() throws InterruptedException {
    }
publicboolean tryLock(long time, TimeUnit unit) throws InterruptedException {
returnfalse;
    }
public Condition newCondition() {
returnnull;
    }}

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
*
*/
publicclass OrderServiceImpl implements Runnable {
privatestatic OrderCodeGenerator ong = new OrderCodeGenerator();
private Logger logger = LoggerFactory.getLogger(OrderServiceImpl.class);
// 同时并发的线程数
privatestaticfinalint NUM = 10;
// 按照线程数初始化倒计数器,倒计数器
privatestatic CountDownLatch cdl = new CountDownLatch(NUM);
private Lock lock = new DistributedLock();
// 创建订单接口
publicvoid 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);
    }
publicvoid 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();
    }
publicstaticvoid 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;
publicclass OrderCodeGenerator {
// 自增长序列
privatestaticint 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
*
*/
publicclass 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
privateint 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
privatevoid 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props
privatevoid 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props
privatevoid addZkListener() {
        TreeCacheListener listener = new TreeCacheListener() {
publicvoid 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;
    }
publicvoid setZkServers(String zkServers) {
this.zkServers = zkServers;
    }
publicvoid setZkPath(String zkPath) {
this.zkPath = zkPath;
    }
publicvoid 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
*
*/
publicclass ZookeeperPlaceholderConfigurer extends PropertyPlaceholderConfigurer {
private ZookeeperConfigurerCentral zkConfigurerCentral;
    @Override
protectedvoid processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
throws BeansException {
        System.out.println(zkConfigurerCentral.getProps());
super.processProperties(beanFactoryToProcess, zkConfigurerCentral.getProps());
    }
publicvoid 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;
publicclass OrderModel implements Serializable {
privatestaticfinallong serialVersionUID = 1L;
privateint orderId;
privateint brandId;
publicint getOrderId() {
return orderId;
    }
publicvoid setOrderId(int orderId) {
this.orderId = orderId;
    }
publicint getBrandId() {
return brandId;
    }
publicvoid setBrandId(int brandId) {
this.brandId = brandId;
    }}

View Code

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
publicclass OrderDao {
    @Autowired
private 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;
            }
        });
    }}

View Code

测试类3：

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

View Code

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
publicclass OrderController {
    @Autowired
private OrderService service;
    @ResponseBody
    @RequestMapping(value = "/test", method = RequestMethod.GET)
public String test() {
        OrderModel p = service.getById();
return p.getBrandId() + "";
    }}

View Code

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=INFO
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayoutlog4j.appender.console.layout.ConversionPattern=%d{MM-dd HH:mm:ss.SSS} [%c:%p] %m%n

View Code

/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.xsd
        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
        http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">
<mvc:default-servlet-handler />
<mvc:annotation-driven
content-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"/>
<bean
class="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"/>
<bean
class="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>
<bean
class="org.springframework.web.servlet.view.json.MappingJackson2JsonView">
<property name="extractValueFromSingleKeyModel" value="true"/>
</bean>
</list>
</property>
</bean></beans>

View Code

/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>

View Code

数据库脚本：

CREATETABLE `tbl_order` (
  `order_id` int(11) NOTNULL AUTO_INCREMENT COMMENT '订单id',
  `brand_id` int(11) DEFAULTNULL COMMENT '品牌id',
PRIMARYKEY (`order_id`)) ENGINE=MyISAM AUTO_INCREMENT=2DEFAULT CHARSET=utf8 COMMENT='订单表';INSERTINTO 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！

以上是 Zookeeper系列四：Zookeeper实现分布式锁、Zookeeper实现配置中心的全部内容，来源链接： utcz.com/z/509512.html

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

1. 分布式锁的实现思路

2. 分布式锁优化后的实现思路

3. Zookeeper分布式锁的代码实现

3.1 Zookeeper分布式锁的核心代码实现

3.2 在业务里面使用分布式锁

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

2. 新建一个zkdemo的maven的web项目

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

2.3 新建一个加载props里面的数据库配置的类

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

2.5 在com.study.demo.controller新建测试类

2.6 其他附加配置和数据库脚本

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

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