Apache Curator Leader选举 简单示例

版本依赖：

<dependency><groupId>org.apache.curator</groupId><artifactId>curator-recipes</artifactId><version>2.10.0</version></dependency>

示例一：

package com.zk.leader;import java.util.ArrayList;import java.util.List;import java.util.concurrent.TimeUnit;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.framework.recipes.leader.LeaderLatch;import org.apache.curator.retry.ExponentialBackoffRetry;/** * 必须启动LeaderLatch: leaderLatch.start(); * 一旦启动， LeaderLatch会和其它使用相同latch path的其它LeaderLatch交涉，然后随机的选择其中一个作为leader。  * 你可以随时查看一个给定的实例是否是leader: */public class Example1{private static final String PATH = "/leader";private static final int COUNT = 5;public static void main(String[] args) throws Exception{CuratorFramework client = CuratorFrameworkFactory.newClient("192.168.1.100:2181", new ExponentialBackoffRetry(1000, 3));client.start();List<LeaderLatch> list = new ArrayList<>();for (int i = 1; i <= COUNT; i++){LeaderLatch example = new LeaderLatch(client, PATH, "Client #" + i);example.start();list.add(example);}TimeUnit.SECONDS.sleep(2);LeaderLatch leader = null;for (LeaderLatch ll : list){if (ll.hasLeadership()){leader = ll;}System.out.println(ll.getId() + "\t" + ll.hasLeadership());};TimeUnit.SECONDS.sleep(2);list.remove(leader);leader.close();TimeUnit.SECONDS.sleep(2);System.out.println("========================");for (LeaderLatch ll : list){System.out.println(ll.getId() + "\t" + ll.hasLeadership());}for (LeaderLatch ll : list){ll.close();}client.close();}}

输出如下：

Client #1falseClient #2falseClient #3trueClient #4falseClient #5false========================Client #1falseClient #2falseClient #4falseClient #5true

示例二：

package com.zk.leader;import java.util.ArrayList;import java.util.List;import java.util.concurrent.TimeUnit;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.LeaderSelectorListenerAdapter;import org.apache.curator.retry.ExponentialBackoffRetry;/** * 与LeaderLatch相比， 通过LeaderSelectorListener可以对领导权进行控制， 在适当的时候释放领导权，这样每个节点都有可能获得领导权。  * 而LeaderLatch一根筋到死， 除非调用close方法，否则它不会释放领导权。 */public class Example2{private static final String PATH = "/leader";private static final int COUNT = 5;public static void main(String[] args) throws Exception{CuratorFramework client = CuratorFrameworkFactory.newClient("192.168.1.100:2181", new ExponentialBackoffRetry(1000, 3));client.start();List<MyLeaderSelectorListenerAdapter> list = new ArrayList<>();for (int i = 1; i <= COUNT; i++){MyLeaderSelectorListenerAdapter example = new MyLeaderSelectorListenerAdapter(client, PATH, "Client #" + i);list.add(example);}TimeUnit.SECONDS.sleep(20);for (MyLeaderSelectorListenerAdapter listener : list){listener.close();}client.close();}}class MyLeaderSelectorListenerAdapter extends LeaderSelectorListenerAdapter{private final String name;    private final LeaderSelector leaderSelector;        public MyLeaderSelectorListenerAdapter(CuratorFramework client, String path, String name)    {    this.name = name;    leaderSelector = new LeaderSelector(client, path, this);        //保证在此实例释放领导权之后还可能获得领导权。    leaderSelector.autoRequeue();        leaderSelector.start();    }        public void close()    {    leaderSelector.close();    }        /**     * 你可以在takeLeadership进行任务的分配等等，并且不要返回，如果你想要要此实例一直是leader的话可以加一个死循环。     * 一旦此方法执行完毕之后，就会重新选举     */public void takeLeadership(CuratorFramework client) throws Exception{System.out.println(name + " 当选为leader");TimeUnit.SECONDS.sleep(2);}}

输出如下：

Client #1 当选为leaderClient #4 当选为leaderClient #2 当选为leaderClient #3 当选为leaderClient #5 当选为leaderClient #1 当选为leaderClient #4 当选为leaderClient #2 当选为leaderClient #3 当选为leaderClient #5 当选为leader

以上是使用curator实现leader的两种方法