Apache ZooKeeper - Leader Election使用场景

妖狐艹你老母 2022-12-28 12:48 144阅读 0赞

### 文章目录 ###

*  需求
 *  Leader Election
 *  Case
 *  Code
 *  源码分析

![在这里插入图片描述][resize_m_lfit_w_962_pic_center]

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# 需求 #

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# Leader Election #

[https://curator.apache.org/getting-started.html][https_curator.apache.org_getting-started.html]

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[Demo示例 ][Demo_]

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# Case #

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官方demo

[https://github.com/apache/curator/tree/master/curator-examples/src/main/java/leader][https_github.com_apache_curator_tree_master_curator-examples_src_main_java_leader]

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 3]

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# Code #

我们自己也写个demo 吧

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<dependency>
                <groupId>org.apache.curator</groupId>
                <artifactId>curator-recipes</artifactId>
                <version>5.0.0</version>
                <exclusions>
                    <exclusion>
                        <groupId>org.apache.zookeeper</groupId>
                        <artifactId>zookeeper</artifactId>
                    </exclusion>
                </exclusions>
            </dependency>
             <dependency>
                <groupId>org.apache.zookeeper</groupId>
                <artifactId>zookeeper</artifactId>
                <version>3.5.8</version>
            </dependency>

import org.apache.curator.RetryPolicy;
    import org.apache.curator.framework.CuratorFramework;
    import org.apache.curator.framework.CuratorFrameworkFactory;
    import org.apache.curator.framework.recipes.leader.LeaderSelector;
    import org.apache.curator.framework.recipes.leader.LeaderSelectorListener;
    import org.apache.curator.framework.recipes.leader.LeaderSelectorListenerAdapter;
    import org.apache.curator.retry.ExponentialBackoffRetry;
    
    import java.util.concurrent.CountDownLatch;
    import java.util.concurrent.TimeUnit;
    
    public class LeaderSelectorTest { 
    
    
        private static  final  String CONNECT_STR="192.168.126.135:2181";
    
    
        private static RetryPolicy retryPolicy=new ExponentialBackoffRetry( 5*1000, 10 );
    
        private  static  CuratorFramework curatorFramework;
    
    
         private static CountDownLatch countDownLatch = new CountDownLatch(1);
    
    
    
        public static void main(String[] args) throws InterruptedException { 
    
    
            String appName = System.getProperty("appName");
    
            CuratorFramework curatorFramework = CuratorFrameworkFactory.newClient(CONNECT_STR, retryPolicy);
            LeaderSelectorTest.curatorFramework = curatorFramework;
            curatorFramework.start();
    
            LeaderSelectorListener listener = new LeaderSelectorListenerAdapter(){ 
                // 选举 leader后的回调
                @Override
                public void takeLeadership(CuratorFramework client) throws Exception
                { 
                    // this callback will get called when you are the leader
                    // do whatever leader work you need to and only exit
                    // this method when you want to relinquish leadership
    
                   System.out.println(" LEADER . 【"+appName +"】, Pre Warm Cache ");
                   // 模拟业务耗时操作
                   TimeUnit.SECONDS.sleep(5);
                }
            };
            LeaderSelector selector = new LeaderSelector(curatorFramework, "/cache_warmer_leader", listener);
            selector.autoRequeue();  // not required, but this is behavior that you will probably expect
            selector.start();
            countDownLatch.await();
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 5]

zk中的数据

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 6]

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# 源码分析 #

我们来看下 curator是怎么实现的？

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70 7]

![在这里插入图片描述][20201217140534183.png]

[resize_m_lfit_w_962_pic_center]: /images/20221120/636db5b71226405d883bed720f2a563f.png
[https_curator.apache.org_getting-started.html]: https://curator.apache.org/getting-started.html
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20201217111532333.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3lhbmdzaGFuZ3dlaQ==,size_16,color_FFFFFF,t_70
[Demo_]: https://github.com/apache/curator/tree/master/curator-examples/src/main/java
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[https_github.com_apache_curator_tree_master_curator-examples_src_main_java_leader]: https://github.com/apache/curator/tree/master/curator-examples/src/main/java/leader
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[20201217140534183.png]: https://img-blog.csdnimg.cn/20201217140534183.png