一句话告诉我Curator是什么?

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(Zookeeper的背景就不在这里介绍了.)
Curator是对ZK的高阶封装. 与操作原生的Zookeeper相比, 它提供了对ZK的完美封装, 简化了对集群的连接, 错误的处理; 实现了一系列经典”模式”, 比如分布式锁, Leader选举等.

既然是为了简单

首先, 获取一个连接实例(CuratorFramework). 对于每个集群, 只需要创建一个实例.

CuratorFrameworkFactory.newClient(zookeeperConnectionString, retryPolicy)

这里我们需要指定一个retryPolicy, 这里用一个指数补偿策略:

RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3)
CuratorFramework client = CuratorFrameworkFactory.newClient(zookeeperConnectionString, retryPolicy);
client.start();

然后我们就可以调用Zookeeper的一系列操作了, 比如创建:

client.create().forPath("/my/path", myData)

这里如果出现了连接问题,curator也会帮你自动重连. 所以, 很简单咯?

我们继续, C/R/U/D:

// this will create the given ZNode with the given data
client.create().forPath(path, payload);

// set data for the given node
client.setData().forPath(path, payload);

// set data for the given node asynchronously. The completion notification
// is done via the CuratorListener.
client.setData().inBackground().forPath(path, payload);

// delete the given node
client.delete().forPath(path);


public static List<String> watchedGetChildren(CuratorFramework client, String path) throws Exception
{
  /**
   * Get children and set a watcher on the node. The watcher notification will come through the
   * CuratorListener (see setDataAsync() above).
   */
  return client.getChildren().watched().forPath(path);
}
        

模式

分布式锁

InterProcessMutex lock = new InterProcessMutex(client, lockPath);
if ( lock.acquire(maxWait, waitUnit) ) 
{
    try 
    {
        // do some work inside of the critical section here
    }
    finally
    {
        lock.release();
    }
}

Leader选举

LeaderSelectorListener listener = new LeaderSelectorListenerAdapter()
{
    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
    }
}

LeaderSelector selector = new LeaderSelector(client, path, listener);
selector.autoRequeue();  // not required, but this is behavior that you will probably expect
selector.start();

事务

        Collection<CuratorTransactionResult>    results = client.inTransaction()
                .create().forPath("/a/path", "some data".getBytes())
            .and()
                .setData().forPath("/another/path", "other data".getBytes())
            .and()
                .delete().forPath("/yet/another/path")
            .and()
                .commit();  // IMPORTANT! The transaction is not submitted until commit() is called

附录

版本

• Curator 2.x.x – ZooKeeper 3.4.x, ZooKeeper 3.5.x
• Curator 3.x.x – 只兼容ZooKeeper 3.5.x; 支持dynamic reconfiguration等新feature.