概述

在單體的應(yīng)用開(kāi)發(fā)場(chǎng)景中涉及并發(fā)同步的時(shí)候馒索，大家往往采用Synchronized（同步）或者其他同一個(gè)JVM內(nèi)Lock機(jī)制來(lái)解決多線程間的同步問(wèn)題。在分布式集群工作的開(kāi)發(fā)場(chǎng)景中名船，就需要一種更加高級(jí)的鎖機(jī)制來(lái)處理跨機(jī)器的進(jìn)程之間的數(shù)據(jù)同步問(wèn)題绰上。這種跨機(jī)器的鎖就是分布式鎖。
用zookeeper來(lái)實(shí)現(xiàn)分布式鎖在分布式系統(tǒng)中是非常常見(jiàn)的場(chǎng)景渠驼。

Curator

Curator是Netflix公司開(kāi)源的一套ZooKeeper客戶(hù)端框架蜈块，提供了一套易用性和可讀性更強(qiáng)的Fluent風(fēng)格的客戶(hù)端API框架
為ZooKeeper客戶(hù)端框架提供了一些比較普遍的、開(kāi)箱即用的迷扇、分布式開(kāi)發(fā)用的解決方案粪狼，例如Recipe闪金、共享鎖服務(wù)、Master選舉機(jī)制和分布式計(jì)算器等者填，幫助開(kāi)發(fā)者避免了“重復(fù)造輪子”的無(wú)效開(kāi)發(fā)工作

Guava is to Java that Curator to ZooKeeper

更多Curator介紹參考：

《Zookeeper開(kāi)源客戶(hù)端框架Curator簡(jiǎn)介》https://www.iteye.com/blog/macrochen-1366136

SpringBoot整合zookeeper澜术、curator

1. 創(chuàng)建springboot項(xiàng)目,在pom.xml文件里加入zookeeper庭再、curator依賴(lài)

<!-- zookeeper -->
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.14</version>
            <exclusions>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>slf4j-log4j12</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>log4j</groupId>
                    <artifactId>log4j</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <!-- curator-framework -->
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-framework</artifactId>
            <version>4.2.0</version>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.zookeeper</groupId>
                    <artifactId>zookeeper</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <!-- curator-recipes -->
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>4.2.0</version>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.curator</groupId>
                    <artifactId>curator-framework</artifactId>
                </exclusion>
            </exclusions>
        </dependency>

完整的pom.xml文件如下

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.zhxin</groupId>
    <artifactId>zkboot</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.1.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.4</version>
            <scope>provided</scope>
        </dependency>

        <!-- zookeeper -->
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <version>3.4.14</version>
            <exclusions>
                <exclusion>
                    <groupId>org.slf4j</groupId>
                    <artifactId>slf4j-log4j12</artifactId>
                </exclusion>
                <exclusion>
                    <groupId>log4j</groupId>
                    <artifactId>log4j</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <!-- curator-framework -->
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-framework</artifactId>
            <version>4.2.0</version>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.zookeeper</groupId>
                    <artifactId>zookeeper</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <!-- curator-recipes -->
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>4.2.0</version>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.curator</groupId>
                    <artifactId>curator-framework</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
</project>

2. 在resource目錄下創(chuàng)建config目錄膳汪，并創(chuàng)建zookeeper.properties配置文件,內(nèi)容如下

zookeeper.server= 127.0.0.1:2181
zookeeper.lockPath = /springboot_zk_lock/

3. 創(chuàng)建org.zhangsan.beans.lock包叙量，并在包里創(chuàng)建AbstractZookeeperLock.java、TestLock.java兩個(gè)類(lèi)
   AbstractZookeeperLock.java

package org.zhangsan.beans.lock;

import java.util.concurrent.TimeUnit;

/**
 * @ClassName AbstractZookeeperLock
 * @Description //AbstractZookeeperLock 鎖
 * @Author singleZhang
 * @Email 405780096@qq.com
 * @Date 2020/12/8 0008 下午 3:17
 **/
public abstract class AbstractZookeeperLock<T> {
    private static final int TIME_OUT = 5;

    public abstract String getLockPath();

    public abstract T execute();

    public int getTimeout(){
        return TIME_OUT;
    }

    public TimeUnit getTimeUnit(){
        return TimeUnit.SECONDS;
    }
}

TestLock.java

package org.zhangsan.beans.lock;

import lombok.Getter;

/**
 * @ClassName TestLock
 * @Description //lock 測(cè)試鎖類(lèi)
 * @Author singleZhang
 * @Email 405780096@qq.com
 * @Date 2020/12/8 0008 下午 3:26
 **/
public abstract class TestLock<String> extends AbstractZookeeperLock<String> {

    private static final java.lang.String LOCK_PATH = "test_";

    @Getter
    private String lockId;

    public TestLock(String lockId) {
        this.lockId = lockId;
    }

    @Override
    public java.lang.String getLockPath() {
        return LOCK_PATH + this.lockId;
    }
}

4. 在org.zhangsan.beans包下隘庄，創(chuàng)建分布式鎖客戶(hù)端類(lèi)文件ZookeeperClient.java

package org.zhangsan.beans;

import lombok.Getter;
import lombok.Setter;
import org.apache.curator.framework.CuratorFramework;
import org.apache.curator.framework.CuratorFrameworkFactory;
import org.apache.curator.framework.recipes.locks.InterProcessMutex;
import org.apache.curator.retry.ExponentialBackoffRetry;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.zhangsan.beans.lock.AbstractZookeeperLock;

/**
 * @ClassName ZookeeperClient
 * @Description // 分布式鎖客戶(hù)端
 * @Author singleZhang
 * @Email 405780096@qq.com
 * @Date 2020/12/8 0008 下午 3:03
 **/
public class ZookeeperClient {
    private static final Logger logger = LoggerFactory.getLogger(ZookeeperClient.class);

    private static final int SLEEP_TIME = 1000;
    private static final int MAX_RETRIES = 3;

    @Getter @Setter
    private String zookeeperServer;
    @Getter @Setter
    private String zookeeperLockPath;

    @Getter
    private CuratorFramework client;

    public ZookeeperClient(String zookeeperServer, String zookeeperLockPath) {
        this.zookeeperServer = zookeeperServer;
        this.zookeeperLockPath = zookeeperLockPath;
    }

    public <T> T lock(AbstractZookeeperLock<T> mutex) {
        String path = this.getZookeeperLockPath() + mutex.getLockPath();
        InterProcessMutex lock = new InterProcessMutex(this.getClient(), path); //創(chuàng)建鎖對(duì)象
        boolean success = false;
        try {
            try {
                success = lock.acquire(mutex.getTimeout(), mutex.getTimeUnit()); //獲取鎖
            } catch (Exception e) {
                throw new RuntimeException("obtain lock error " + e.getMessage() + ", path " + path);
            }
            if (success) {
                return (T) mutex.execute();
            } else {
                return null;
            }
        } finally {
            try {
                if (success){
                    lock.release(); //釋放鎖
                }
            } catch (Exception e) {
                logger.error("release lock error {}, path {}", e.getMessage(), path);
            }
        }
    }

    public void init() {
        this.client = CuratorFrameworkFactory
                .builder()
                .connectString(this.getZookeeperServer())
                .retryPolicy(new ExponentialBackoffRetry(SLEEP_TIME, MAX_RETRIES))
                .build();
        this.client.start();
    }

    public void destroy() {
        try {
            if (getClient() != null) {
                getClient().close();
            }
        } catch (Exception e) {
            logger.error("stop zookeeper client error {}", e.getMessage());
        }
    }
}

5. 創(chuàng)建org.zhangsan.config包,并在包中創(chuàng)建ZookeeperConfig.java配置類(lèi)

package org.zhangsan.config;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.core.env.Environment;
import org.zhangsan.beans.ZookeeperClient;

/**
 * @ClassName ZookeeperConfig
 * @Description //Zookeeper 配置類(lèi)
 * @Author singleZhang
 * @Email 405780096@qq.com
 * @Date 2020/12/8 0008 下午 2:52
 **/
@Configuration
@PropertySource("classpath:config/zookeeper.properties")
public class ZookeeperConfig {

    @Autowired
    private Environment environment;

    @Bean(initMethod = "init", destroyMethod = "destroy")
    public ZookeeperClient zookeeperClient(){
        String zookeeperServer = environment.getRequiredProperty("zookeeper.server");
        String zookeeperLockPath = environment.getRequiredProperty("zookeeper.lockPath");
        return new ZookeeperClient(zookeeperServer, zookeeperLockPath);
    }

}

6.啟動(dòng)文件ZkBootApplication.java

package org.zhangsan;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;


@SpringBootApplication(exclude= {DataSourceAutoConfiguration.class})
public class ZkBootApplication {
    public static void main(String[] args){
        SpringApplication.run(ZkBootApplication.class,args);
    }
}

7. 接下來(lái)測(cè)試一下鎖的功能是否能正常運(yùn)行,在test目錄下創(chuàng)建org.zhangsan.zookeeper包踢步，并創(chuàng)建ZkLockTest.java測(cè)試類(lèi)

package org.zhangsan.zookeeper;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import org.zhangsan.beans.ZookeeperClient;
import org.zhangsan.beans.lock.TestLock;

/**
 * @ClassName ZkLockTest
 * @Description //Zookeeper鎖測(cè)試
 * @Author singleZhang
 * @Email 405780096@qq.com
 * @Date 2020/12/8 0008 下午 3:30
 **/
@RunWith(SpringRunner.class)
@SpringBootTest
public class ZkLockTest {

    @Autowired
    private ZookeeperClient zookeeperClient;

    @Test
    public void zookeeperLockTest(){
        String lockId = "123123";
        String result = zookeeperClient.lock(new TestLock<String>(lockId) {
            @Override
            public String execute() {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                return this.getLockId();
            }
        });

        if (result == null) {
            System.out.println("執(zhí)行失敗");
        } else {
            System.out.println("執(zhí)行成功");
        }
    }
}

8. 啟動(dòng)之前配置好的zookeeper集群,運(yùn)行項(xiàng)目癣亚，測(cè)試
   運(yùn)行成功丑掺，并同時(shí)間更新日志文件

   
   
   分布式鎖測(cè)試結(jié)果
   
   

   日志為最新時(shí)間

   
   
   日志

9. 在zookeeper日志目錄里查看日志
   因?yàn)閦ookeeper的日志文件為二進(jìn)制文件，這里需要用到兩個(gè)jar包:/slf4j-api-1.7.25.jar述雾、zookeeper-3.4.14.jar
   LogFormatter 為用到的格式化類(lèi)街州。
   查看命令如下:

>java -classpath lib/slf4j-api-1.7.25.jar:zookeeper-3.4.14.jar org.apache.zookeeper.server.LogFormatter E:/zookeeper/zookeeper-3.4.14/log/zoo-1/version-2/log.200000001

總結(jié)

ZooKeeper分布式鎖：

• 優(yōu)點(diǎn)
  ZooKeeper分布式鎖（如InterProcessMutex）兼丰，能有效地解決分布式問(wèn)題，不可重入問(wèn)題唆缴，使用起來(lái)也較為簡(jiǎn)單
• 缺點(diǎn)
  ZooKeeper實(shí)現(xiàn)的分布式鎖鳍征，性能并不太高。
  因?yàn)槊看卧趧?chuàng)建鎖和釋放鎖的過(guò)程中面徽，都要?jiǎng)討B(tài)創(chuàng)建艳丛、銷(xiāo)毀暫時(shí)節(jié)點(diǎn)來(lái)實(shí)現(xiàn)鎖功能，
  Zk中創(chuàng)建和刪除節(jié)點(diǎn)只能通過(guò)Leader（主）服務(wù)器來(lái)執(zhí)行趟紊，然后Leader服務(wù)器還需要將數(shù)據(jù)同步到所有的Follower（從）服務(wù)器上氮双，這樣頻繁的網(wǎng)絡(luò)通信，系統(tǒng)性能會(huì)下降霎匈。
  總之戴差，在高性能、高并發(fā)的應(yīng)用場(chǎng)景下铛嘱，不建議使用ZooKeeper的分布式鎖暖释，而由于ZooKeeper的高可用性，因此在并發(fā)量不是太高的應(yīng)用場(chǎng)景中墨吓，還是推薦使用ZooKeeper的分布式鎖球匕。

目前分布式鎖，比較成熟肛真、主流的方案有兩種：

• 基于Redis的分布式鎖谐丢。適用于并發(fā)量很大、性能要求很高而可靠性問(wèn)題可以通過(guò)其他方案去彌補(bǔ)的場(chǎng)景蚓让。
• 基于ZooKeeper的分布式鎖乾忱。適用于高可靠，而并發(fā)量不是太高的場(chǎng)景
  在選型時(shí)历极，選擇適合于自己業(yè)務(wù)場(chǎng)景的方案即可窄瘟。

項(xiàng)目代碼地址:
https://gitee.com/kaixinshow/springboot-note

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