CuratorFramework使用

CuratorFramework

Framework

是ZooKeeper Client更高的抽象API
自动连接管理:
1. 当ZooKeeper客户端内部出现异常, 将自动进行重连或重试, 该过程对外几乎完全透明
2. 监控节点数据变化事件NodeDataChanged，需要时调用updateServerList()方法
3. Curator recipes自动移除监控

更清晰的API: 简化了ZooKeeper原生的方法, 事件等, 提供流式fluent的接口
提供Recipes实现 : 选举，共享锁， 路径cache， 分布式队列，分布式优先队列等

CuratorFrameworkFactory类提供了两个方法, 一个工厂方法newClient, 一个构建方法build. 使用工厂方法newClient可以创建一个默认的实例, 而build构建方法可以对实例进行定制. 当CuratorFramework实例构建完成, 紧接着调用start()方法, 在应用结束的时候, 需要调用close()方法. CuratorFramework是线程安全的. 在一个应用中可以共享同一个zk集群的CuratorFramework.

CuratorFramework API采用了连贯风格的接口(Fluent Interface). 所有的操作一律返回构建器, 当所有元素加在一起之后, 整个方法看起来就像一个完整的句子. 比如下面的操作:

client.create().forPath("/head")client.delete().inBackground().forPath("/head")client.create().withMode(CreateMode.EPHEMERAL_SEQUENTIAL).forPath("/head/child")client.getData().watched().inBackground().forPath("/test")

方法说明:
create(): 发起一个create操作. 可以组合其他方法 (比如mode 或background) 最后以forPath()方法结尾
delete(): 发起一个删除操作. 可以组合其他方法(version 或background) 最后以forPath()方法结尾
checkExists(): 发起一个检查ZNode 是否存在的操作. 可以组合其他方法(watch 或background) 最后以forPath()方法结尾
getData(): 发起一个获取ZNode数据的操作. 可以组合其他方法(watch, background 或get stat) 最后以forPath()方法结尾
setData(): 发起一个设置ZNode数据的操作. 可以组合其他方法(version 或background) 最后以forPath()方法结尾
getChildren(): 发起一个获取ZNode子节点的操作. 可以组合其他方法(watch, background 或get stat) 最后以forPath()方法结尾
inTransaction(): 发起一个ZooKeeper事务. 可以组合create, setData, check, 和/或delete 为一个操作, 然后commit() 提交

通知(Notification)

通过ClientListener实现。 通过CuratorFramework实例里的addListener()注册listener. listener实现以下方法：
- eventReceived() 当一个后台操作完成或者指定的watch被触发时该方法被调用

CuratorEvent

CuratorEvent(在以前版本为ClientEvent)是对各种操作触发相关事件对象(POJO)的一个完整封装, 而事件对象的内容跟事件类型相关, 事件类型可通过getType()获得。下面是对应关系:

名称空间(Namespace)

因为一个zk集群会被多个应用共享, 为了避免各个应用的zk patch冲突, Curator Framework内部会给每一个Curator Framework实例分配一个namespace(可选). 这样你在create ZNode的时候都会自动加上这个namespace作为这个node path的root. 使用代码如下:

CuratorFramework client = CuratorFrameworkFactory.builder().namespace("MyApp") ... build(); …client.create().forPath("/test", data);// 实际上节点路径为: "/MyApp/test"

临时连接

Curator还提供了临时的CuratorFramework： CuratorTempFramework，意思是在一个容易失败的网络如WAN中，向zooKeeper的单一请求。 一定时间不活动后连接会被关闭，只提供了有限的api. 临时 CuratorFramework基于Camille Fournier的一篇文章：http://whilefalse.blogspot.com/2012/12/building-global-highly-available.html.

创建builder时不是调用build()而是调用buildTemp()。 3分钟不活动连接就被关闭，也可以指定不活动的时间。 它只提供了下面几个方法：

 /**     * Stop the client     */    public void     close();    /**     * Start a transaction builder     *     * @return builder object     * @throws Exception errors     */    public CuratorTransaction inTransaction() throws Exception;    /**     * Start a get data builder     *     * @return builder object     * @throws Exception errors     */    public TempGetDataBuilder getData() throws Exception;

创建实例

两种方法，newClient()或build()，实例如下,来自于官网

/** * Licensed to the Apache Software Foundation (ASF) under one * or more contributor license agreements.  See the NOTICE file * distributed with this work for additional information * regarding copyright ownership.  The ASF licenses this file * to you under the Apache License, Version 2.0 (the * "License"); you may not use this file except in compliance * with the License.  You may obtain a copy of the License at * *   http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, * software distributed under the License is distributed on an * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY * KIND, either express or implied.  See the License for the * specific language governing permissions and limitations * under the License. */package framework;import org.apache.curator.RetryPolicy;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.retry.ExponentialBackoffRetry;public class CreateClientExamples{    public static CuratorFramework createSimple(String connectionString)    {        // these are reasonable arguments for the ExponentialBackoffRetry. The first        // retry will wait 1 second - the second will wait up to 2 seconds - the        // third will wait up to 4 seconds.        ExponentialBackoffRetry retryPolicy = new ExponentialBackoffRetry(1000, 3);        // The simplest way to get a CuratorFramework instance. This will use default values.        // The only required arguments are the connection string and the retry policy        return CuratorFrameworkFactory.newClient(connectionString, retryPolicy);    }    public static CuratorFramework  createWithOptions(String connectionString, RetryPolicy retryPolicy, int connectionTimeoutMs, int sessionTimeoutMs)    {        // using the CuratorFrameworkFactory.builder() gives fine grained control        // over creation options. See the CuratorFrameworkFactory.Builder javadoc        // details        return CuratorFrameworkFactory.builder()            .connectString(connectionString)            .retryPolicy(retryPolicy)            .connectionTimeoutMs(connectionTimeoutMs)            .sessionTimeoutMs(sessionTimeoutMs)            // etc. etc.            .build();    }}

CRUD操作,来自于官网

package com.colobu.zkrecipe.framework;import java.util.List;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.api.BackgroundCallback;import org.apache.curator.framework.api.CuratorEvent;import org.apache.curator.framework.api.CuratorListener;import org.apache.zookeeper.CreateMode;import org.apache.zookeeper.Watcher;public class CrudExample {    public static void main(String[] args) {    }    public static void create(CuratorFramework client, String path, byte[] payload) throws Exception {        // this will create the given ZNode with the given data        client.create().forPath(path, payload);    }    public static void createEphemeral(CuratorFramework client, String path, byte[] payload) throws Exception {        // this will create the given EPHEMERAL ZNode with the given data        client.create().withMode(CreateMode.EPHEMERAL).forPath(path, payload);    }    public static String createEphemeralSequential(CuratorFramework client, String path, byte[] payload) throws Exception {        // this will create the given EPHEMERAL-SEQUENTIAL ZNode with the given        // data using Curator protection.        return client.create().withProtection().withMode(CreateMode.EPHEMERAL_SEQUENTIAL).forPath(path, payload);    }    public static void setData(CuratorFramework client, String path, byte[] payload) throws Exception {        // set data for the given node        client.setData().forPath(path, payload);    }    public static void setDataAsync(CuratorFramework client, String path, byte[] payload) throws Exception {        // this is one method of getting event/async notifications        CuratorListener listener = new CuratorListener() {            @Override            public void eventReceived(CuratorFramework client, CuratorEvent event) throws Exception {                // examine event for details            }        };        client.getCuratorListenable().addListener(listener);        // set data for the given node asynchronously. The completion        // notification        // is done via the CuratorListener.        client.setData().inBackground().forPath(path, payload);    }    public static void setDataAsyncWithCallback(CuratorFramework client, BackgroundCallback callback, String path, byte[] payload) throws Exception {        // this is another method of getting notification of an async completion        client.setData().inBackground(callback).forPath(path, payload);    }    public static void delete(CuratorFramework client, String path) throws Exception {        // delete the given node        client.delete().forPath(path);    }    public static void guaranteedDelete(CuratorFramework client, String path) throws Exception {        // delete the given node and guarantee that it completes        client.delete().guaranteed().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);    }    public static List<String> watchedGetChildren(CuratorFramework client, String path, Watcher watcher) throws Exception {        /**         * Get children and set the given watcher on the node.         */        return client.getChildren().usingWatcher(watcher).forPath(path);    }}

事务

CuratorFramework提供了事务的概念，可以将一组操作放在一个原子事务中。事务是原子的， 一组操作要么都成功，要么都失败。

package com.colobu.zkrecipe.framework;import java.util.Collection;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.api.transaction.CuratorTransaction;import org.apache.curator.framework.api.transaction.CuratorTransactionFinal;import org.apache.curator.framework.api.transaction.CuratorTransactionResult;public class TransactionExample {    public static void main(String[] args) {    }    public static Collection<CuratorTransactionResult> transaction(CuratorFramework client) throws Exception {        // this example shows how to use ZooKeeper's new transactions        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        for (CuratorTransactionResult result : results) {            System.out.println(result.getForPath() + " - " + result.getType());        }        return results;    }    /*     * These next four methods show how to use Curator's transaction APIs in a     * more traditional - one-at-a-time - manner     */    public static CuratorTransaction startTransaction(CuratorFramework client) {        // start the transaction builder        return client.inTransaction();    }    public static CuratorTransactionFinal addCreateToTransaction(CuratorTransaction transaction) throws Exception {        // add a create operation        return transaction.create().forPath("/a/path", "some data".getBytes()).and();    }    public static CuratorTransactionFinal addDeleteToTransaction(CuratorTransaction transaction) throws Exception {        // add a delete operation        return transaction.delete().forPath("/another/path").and();    }    public static void commitTransaction(CuratorTransactionFinal transaction) throws Exception {        // commit the transaction        transaction.commit();    }}

自己写的练习

1) 新建 maven项目，添加依赖，添加curator-recipes即可

     <dependency >      <groupId >org.apache.curator </ groupId>      <artifactId > curator-recipes</ artifactId >      <version >2.6.0 </ version>    </dependency >

2) 采用CuratorFrameworkFactory.newClient() 或者 build() 方式 创建CuratorFramework实例，如下所示：

RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);               CuratorFramework client;         //      client= CuratorFrameworkFactory.newClient(CONNECTSTRING, retryPolicy);               client=CuratorFrameworkFactory. builder().                           connectString( CONNECTSTRING )                           .connectionTimeoutMs(30000)                           .sessionTimeoutMs(30000)                           .canBeReadOnly( false ).retryPolicy(retryPolicy)                           .namespace( NAMESPACE )                           .defaultData( null )                           .build();

3) client.start() 启动，结束时调用client.close() 关闭
4) 通过fluent方式进行相关操作，如下增删改查:

     client.create().forPath( PATH, "hello world" .getBytes());     byte [] bs=client.getData().forPath( PATH);     System. out.println( "新建的节点,data为: " + new String(bs));     client.setData().forPath( PATH ,"hello china".getBytes());     // 由于是在background模式下获取的data，此时的 bs可能为null     byte [] bs2=client.getData().watched().inBackground().forPath( PATH);    System. out.println( "新修改的节点,data为: " + new String(bs2!=null ? bs2 : new byte[0]));   client.delete().forPath( PATH );

完整代码如下:

package curator;import org.apache.curator.RetryPolicy;import org.apache.curator.framework.CuratorFramework;import org.apache.curator.framework.CuratorFrameworkFactory;import org.apache.curator.retry.ExponentialBackoffRetry;import org.apache.curator.utils.CloseableUtils;import org.apache.zookeeper.data.Stat;public class CuratorClientExample {        public static String CONNECTSTRING= "127.0.0.1:2181";        public static String PATH= "/crud";        public static String NAMESPACE= "fortest";        public static void main(String[] args) {               RetryPolicy retryPolicy = new ExponentialBackoffRetry(1000, 3);               CuratorFramework client;         //      client= CuratorFrameworkFactory.newClient(CONNECTSTRING, retryPolicy);               client=CuratorFrameworkFactory. builder().                           connectString( CONNECTSTRING )                           .connectionTimeoutMs(30000)                           .sessionTimeoutMs(30000)                           .canBeReadOnly( false ).retryPolicy(retryPolicy)                           .namespace( NAMESPACE )                           .defaultData( null )                           .build();               client.start();               try {                           client.create().forPath( PATH ,"hello world".getBytes());                            byte [] bs=client.getData().forPath( PATH);                           System. out .println("新建的节点,data为: " + new String(bs));                           client.setData().forPath( PATH ,"hello china".getBytes());                            // 由于是在background模式下获取的data，此时的 bs可能为null                             byte [] bs2=client.getData().watched().inBackground().forPath( PATH);                           System. out .println("新修改的节点,data为: " + new String(bs2!=null ? bs2 : new byte[0]));                           client.delete().forPath( PATH );                           Stat stat=client.checkExists().forPath( PATH );                            // Stat 就是对zonde所有属性的一个映射， stat=null表示节点不存在！                            System. out .println(stat);                    } catch (Exception e) {                            // TODO Auto-generated catch block                           e.printStackTrace();                    } finally {                           CloseableUtils. closeQuietly(client);                    }            }}

参考资料：
- http://curator.apache.org/curator-framework/index.html
- http://supben.iteye.com/blog/2094077
- http://macrochen.iteye.com/blog/1366136