使用Apache Curator包实现基于zookeeper的分布式锁与验证

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Apache Curator包是对zookeeper的java API的包装，使我们更方便使用分布式锁，分布式锁是使用zookeeper的【临时】【有序】节点特效来完成的

Curator分布式锁过程：

	1.先设置分布式锁在zookeeper中的路径/curator/lock
	2.mutex.acquire() 获取锁，失败抛异常，
		先看当前线程是否已经获取过锁(可重入)，若有锁了，就增加获取计数
		否则尝试去加锁 (create),因为有序，所以判断是否为最小序号
		看看自己创建的节点序号是否最小 最小则获得分布式锁 否则继续监听
	3.mutex.release()释放锁，因为acquire会计数，所以acquire与release必须成对

Curator包依赖于zookeeper包，注意版本兼容问题
Apache Curator–ZooKeeper Version Compatibility

下面使用两个类来验证分布式锁

	test.java 先使用分布式锁，睡眠
	test2.java 使用同一锁会等待，直到test.java完成
	注意test.java与test2.java的ip地址不同，验证zookeeper的集群连接

//pom.xml
<?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>com.dddd</groupId>
    <artifactId>maventest</artifactId>
    <version>1.0</version>

    <dependencies>
        <dependency>
            <groupId>org.apache.curator</groupId>
            <artifactId>curator-recipes</artifactId>
            <version>4.0.0</version>
            <exclusions>
                <exclusion>
                    <groupId>org.apache.zookeeper</groupId>
                    <artifactId>zookeeper</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.apache.zookeeper</groupId>
            <artifactId>zookeeper</artifactId>
            <!-- same version with the zookeeper-->
            <version>3.4.13</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

//test.java
import org.apache.curator.RetryPolicy;
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;


public class Test {

    public static void main(String[] args) throws Exception{

        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);

        CuratorFramework client = CuratorFrameworkFactory.newClient("192.168.11.131:2181", retryPolicy);

        client.start();

        //create distro lock on node "/curator/lock" in zookeeper
        InterProcessMutex mutex = new InterProcessMutex(client, "/curator/lock");
        mutex.acquire();

        System.out.println("Enter mutex");
        Thread.sleep(10000);
        
        mutex.release();
        
        client.close();
    }
}

//test2.java
import org.apache.curator.RetryPolicy;
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;


public class Test2 {

    public static void main(String[] args) throws Exception{

        RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);

        CuratorFramework client = CuratorFrameworkFactory.newClient("192.168.11.132:2181", retryPolicy);

        client.start();

        //create distro lock on node "/curator/lock" in zookeeper
        InterProcessMutex mutex = new InterProcessMutex(client, "/curator/lock");
        mutex.acquire();

        System.out.println("Enter mutex");

        mutex.release();

        client.close();
    }
}