zookeeper最经典的用法，选举。Curator的实现有2个种：

LeaderLatch：

这种是有阻塞的，就是大家一起上，谁先上了，就一直阻塞着，直到方法执行完成。如果执行结束，那么其他的兄弟就选一个出来。我觉得这种适合主备，比如开2 个 job，一个挂了另一个就上。

代码，这种代码最好是开2个eclipse看效果，顺序打开，看效果，再领悟：

package curator.selector;import org.apache.curator.RetryPolicy;
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;public class LeaderLatchDemo {public static void main(String[] args) throws Exception {RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181").sessionTimeoutMs(2000).connectionTimeoutMs(10000).retryPolicy(retryPolicy).namespace("text").build();client.start();// 选举Leader 启动LeaderLatch latch = new LeaderLatch(client,"/path");latch.start();latch.await();System.err.println("我启动了");Thread.currentThread().sleep(1000000);latch.close();client.close();}
}

LeaderSelector：

这种复杂一点，他有个leaderSelector.autoRequeue();就是自动抢，比如打印一个helloworld，第一个打印完，第2个打印，然后第3个打印。然后第一个再打印，大家一起抢。有点动态选举的味道。

代码：

package curator.selector;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.LeaderSelectorListenerAdapter;
import org.apache.curator.retry.ExponentialBackoffRetry;public class LeaderSelectorDemo {public static void main(String[] args) throws Exception {RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);final CuratorFramework client = CuratorFrameworkFactory.builder().connectString("127.0.0.1:2181").sessionTimeoutMs(5000).connectionTimeoutMs(10000).retryPolicy(retryPolicy).namespace("text").build();client.start();final LeaderSelector leaderSelector = new LeaderSelector(client, "/led", new LeaderSelectorListenerAdapter(){@Overridepublic void takeLeadership(CuratorFramework client) throws Exception {System.err.println("work ing...");Thread.currentThread().sleep(3000);System.err.println("end");}});leaderSelector.autoRequeue();leaderSelector.start();System.in.read();}
}