zookeeper-Curator use

ZK commonly used in three ways:

　　1, using native API Zookeeper

　　2, ZkClient 

　　3, using Curator  

Curator is open source Netflix, a Zookeeper client, compared with Zookeeper provide native client, a higher level of abstraction Curator, and simplifies the development of the amount Zookeeper client.

• ZooKeeper client connection between the package and ZooKeeper server process;

• Providing a Fluent style operation the API;

• ZooKeeper provides a variety of application scenarios (recipe, such as shared locks service, the cluster leadership election mechanism) abstract package.

 

Curator several components

• Client: is a substitute ZooKeeper client provides some underlying processing tools and related methods.

• Framework: to simplify the use of advanced features ZooKeeper, and adds some new features, such as managing the connection to ZooKeeper cluster, retry processing.

• Recipes: to achieve a common recipe ZooKeeper, the assembly is based on the Framework

• Utilities: ZooKeeper variety of tools.

• Errors: exception handling, connection recovery.

• Extensions: recipe expansion

RetryPolicy connection policy

• RetryOneTime: reconnection only once.

• RetryNTime: Specifies the number of times reconnection N.

• RetryUtilElapsed: Specifies the maximum reconnection timeout and reconnection time interval, intermittent reconnection until a timeout or link success.

• ExponentialBackoffRetry: based on "backoff (retracted)" mode reconnection, and RetryUtilElapsed difference is reconnection interval is dynamic.

• BoundedExponentialBackoffRetry: with ExponentialBackoffRetry, increased control the maximum number of retries.

Create Session

CuratorFrameworkFactory.newClient(String connectString, int sessionTimeoutMs, 
                int connectionTimeoutMs, RetryPolicy retryPolicy)

CuratorFrameworkFactory.builder().connectString("192.168.11.56:2180")  
            .sessionTimeoutMs(30000).connectionTimeoutMs(30000)  
            .canBeReadOnly(false)  
            .retryPolicy(new ExponentialBackoffRetry(1000, Integer.MAX_VALUE))
            .build();

 

Creating nodes

client.create().creatingParentIfNeeded()
        .withMode(CreateMode.PERSISTENT)
        .withACL(aclList)
        .forPath(path, "hello, zk".getBytes());

 

Delete Node

client.delete().guaranteed().deletingChildrenIfNeeded().withVersion(version).forPath(path)

 

Gets node

client.getData().storingStatIn(stat).forPath(path);

client.getChildren().forPath(path);

 

Updates node

client.setData().withVersion(version).forPath(path, data)

 

Determine whether there is a node

client.checkExists().forPath(path)；

 

Setting permissions

Build.authorization(String scheme, byte[] auth)
client.setACL().withVersion(version)
        .withACL(ZooDefs.Ids.CREATOR_ALL_ACL)
        .forPath(path);

 

Monitor

Cache is the curator of the event listener packaging, listen for the event can be seen as an approximate comparison process local cache view and remote view of ZK

• NodeCache for caching node processing node itself changes, the callback interface NodeCacheListener

• Child nodes changes PathChildrenCache child node caching nodes for processing, the callback interface PathChildrenCacheListener

• TreeCache / NodeCache and PathChildrenCache combination, the callback interface TreeCacheListener

NodeCache nc = new NodeCache(client, path, false);
        nc.start();
        nc.getListenable().addListener(new NodeCacheListener() {
            @Override
            public void nodeChanged() throws Exception {
                ...
            }
        });