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

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

                 
      
       com.101tec
                  
      
       zkclient
                  
      
       0.10
              
     

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
     
       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beforePath        else {            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    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 rootcreate /Jdbc/password 123456create /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：

         
      
       4.0.0
          
      
       com.study.demo
          
      
       zkdemo
          
      
       war
          
      
       0.0.1-SNAPSHOT
          
      
       zkdemo Maven Webapp
          
      
       http://maven.apache.org
          
              
       
        4.3.8.RELEASE
           
          
              
                   
        
         junit
                    
        
         junit
                    
        
         3.8.1
                    
        
         test
                
               
                   
        
         org.apache.zookeeper
                    
        
         zookeeper
                    
        
         3.4.10
                
               
                   
        
         com.101tec
                    
        
         zkclient
                    
        
         0.10
                
               
                   
        
         org.apache.curator
                    
        
         curator-framework
                    
        
         4.0.0
                
               
                   
        
         org.apache.curator
                    
        
         curator-recipes
                    
        
         4.0.0
                
               
                   
        
         javax.servlet
                    
        
         javax.servlet-api
                    
        
         3.1.0
                
               
                   
        
         org.apache.tomcat
                    
        
         tomcat-catalina
                    
        
         7.0.39
                
               
                   
        
         org.springframework
                    
        
         spring-core
                    
        
         ${spring.version}
                
               
                   
        
         org.springframework
                    
        
         spring-beans
                    
        
         ${spring.version}
                
               
                   
        
         org.springframework
                    
        
         spring-jdbc
                    
        
         ${spring.version}
                
               
                   
        
         org.springframework
                    
        
         spring-context
                    
        
         ${spring.version}
                
               
                   
        
         org.springframework
                    
        
         spring-web
                    
        
         ${spring.version}
                
               
                   
        
         org.springframework
                    
        
         spring-webmvc
                    
        
         ${spring.version}
                
               
                   
        
         com.zaxxer
                    
        
         HikariCP
                    
        
         2.7.1
                
               
                   
        
         mysql
                    
        
         mysql-connector-java
                    
        
         5.1.41
                
               
                   
        
         org.slf4j
                    
        
         slf4j-api
                    
        
         1.7.25
                
               
                   
        
         org.slf4j
                    
        
         jcl-over-slf4j
                    
        
         1.7.25
                
               
                   
        
         log4j
                    
        
         log4j
                    
        
         1.2.17
                
               
                   
        
         com.fasterxml.jackson.core
                    
        
         jackson-core
                    
        
         2.9.1
                
               
                   
        
         com.fasterxml.jackson.core
                    
        
         jackson-databind
                    
        
         2.9.1
                
               
                   
        
         javax.servlet
                    
        
         jstl
                    
        
         1.2
                
           
          
              
       
        zkdemo
           
      
     

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props    private void getConfigData() {        try {            List
     
       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    private 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：* 
     * @author leeSmall* @date 2018年9月10日**/public class ZookeeperPlaceholderConfigurer extends PropertyPlaceholderConfigurer {    private ZookeeperConfigurerCentral zkConfigurerCentral;    @Override    protected 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

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;@Repositorypublic class OrderDao {    @Autowired    private JdbcTemplate jdbcTemplate;    public OrderModel findById() {        String sql = "select * from tbl_order where order_id = 1";        return jdbcTemplate.queryForObject(sql, new RowMapper
      
       () {            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;@Servicepublic class OrderService {    @Autowired    private 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;@Controllerpublic class OrderController {    @Autowired    private 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,consolelog4j.logger.org.apache.zookeeper=DEBUGlog4j.logger.org.apache.curator=DEBUGlog4j.logger.java.lang.Exception=INFOlog4j.appender.console=org.apache.log4j.ConsoleAppenderlog4j.appender.console.layout=org.apache.log4j.PatternLayoutlog4j.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

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

      
          
       
        zkdemo
           
       
        Zookeeper Demo Application
           
           
           
           
               
        
         webAppRootKey
                
        
         zkdemo.root
            
           
               
        
         log4jConfigLocation
                
        
         /WEB-INF/config/log4j.properties
            
           
               
        
         log4jRefreshInterval
                
        
         60000
            
           
               
        
         contextConfigLocation
                
        
         /WEB-INF/config/applicationContext.xml
            
           
               
        
         spring
                
        
         org.springframework.web.servlet.DispatcherServlet
                
                    
         
          contextConfigLocation
                     
         
          /WEB-INF/config/spring-mvc.xml
                 
                
        
         1
            
           
               
        
         spring
                
        
         /
            
           
           
           
           
               
        
         org.springframework.web.util.Log4jConfigListener
            
           
               
        
         org.springframework.web.context.ContextLoaderListener
            
           
           
           
           
               
        
         characterEncodingFilter
                
        
         org.springframework.web.filter.CharacterEncodingFilter
                
                    
         
          encoding
                     
         
          UTF-8
                 
                
                    
         
          forceEncoding
                     
         
          true
                 
            
           
               
        
         characterEncodingFilter
                
        
         /*
            
           
           
           
           
               
        
         20
            
           
           
           
           
               
        
         403
                
        
         /403.jsp
            
           
               
        
         404
                
        
         /404.jsp
            
           
               
        
         500
                
        
         /500.jsp
            
           
           
           
           
               
        
         index.htm
                
        
         index.jsp
            
       
      

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！