Apache Curator Leader选举简单示例

旧城等待， 2022-08-22 06:26 187阅读 0赞

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

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

以上是使用curator实现leader的两种方法