一句話(huà)告訴我Curator是什么?

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(Zookeeper的背景就不在這里介紹了.)
Curator是對(duì)ZK的高階封裝. 與操作原生的Zookeeper相比, 它提供了對(duì)ZK的完美封裝, 簡(jiǎn)化了對(duì)集群的連接, 錯(cuò)誤的處理; 實(shí)現(xiàn)了一系列經(jīng)典"模式", 比如分布式鎖, Leader選舉等.

既然是為了簡(jiǎn)單

首先, 獲取一個(gè)連接實(shí)例(CuratorFramework). 對(duì)于每個(gè)集群, 只需要?jiǎng)?chuàng)建一個(gè)實(shí)例.

CuratorFrameworkFactory.newClient(zookeeperConnectionString, retryPolicy)

這里我們需要指定一個(gè)retryPolicy, 這里用一個(gè)指數(shù)補(bǔ)償策略:

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

然后我們就可以調(diào)用Zookeeper的一系列操作了, 比如創(chuàng)建:

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

這里如果出現(xiàn)了連接問(wèn)題,curator也會(huì)幫你自動(dòng)重連. 所以, 很簡(jiǎn)單咯?

我們繼續(xù), 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

分布式鎖

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選舉

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();

事務(wù)

        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

附錄

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.