zk 08之：Curator之一：zk客户端Curator

Curator是Netflix公司开源的一个Zookeeper客户端，与Zookeeper提供的原生客户端相比，Curator的抽象层次更高，简化了Zookeeper客户端编程。

它包含以下几个组件：

Component	description
Recipes	Implementations of some of the common ZooKeeper “recipes”. The implementations are built on top of the Curator Framework.
Framework	The Curator Framework is a high-level API that greatly simplifies using ZooKeeper. It adds many features that build on ZooKeeper and handles the complexity of managing connections to the ZooKeeper cluster and retrying operations.
Utilities	Various utilities that are useful when using ZooKeeper.
Client	A replacement for the bundled ZooKeeper class that takes care of some low-level housekeeping and provides some useful utilities.
Errors	How Curator deals with errors, connection issues, recoverable exceptions, etc.
Extensions	The curator-recipes package implements the common recipes that are described in the ZooKeeper documentation. To avoid bloating that package, recipes/applications that have a vertical appeal will be put in separate “extension” packages using the naming convention curator-x-name.

示例：

<?xml version="1.0"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.sf.zkclient</groupId>
  <artifactId>zkclient</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <name>zkclient</name>
  <url>http://maven.apache.org</url>
  <properties>
      <curator.version>2.11.1</curator.version>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>
  <dependencies>
    <dependency>
        <groupId>org.apache.zookeeper</groupId>
        <artifactId>zookeeper</artifactId>
        <version>3.4.8</version>
        <exclusions>
            <exclusion>
                <artifactId>slf4j-log4j12</artifactId>
                <groupId>org.slf4j</groupId>
            </exclusion>
            <exclusion>
                <artifactId>log4j</artifactId>
                <groupId>log4j</groupId>
            </exclusion>
        </exclusions>
    </dependency>

    <dependency>
        <groupId>org.apache.curator</groupId>
        <artifactId>curator-framework</artifactId>
        <version>${curator.version}</version>
    </dependency>
    <dependency>
        <groupId>org.apache.curator</groupId>
        <artifactId>curator-client</artifactId>
        <version>${curator.version}</version>
        <exclusions>
            <exclusion>
                <groupId>com.google.guava</groupId>
                <artifactId>guava</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

    <dependency>
        <groupId>com.google.guava</groupId>
        <artifactId>guava</artifactId>
        <version>18.0</version>
    </dependency>
</dependencies>
</project>

java代码：

示例一：常见的添加、修改、删除示例：

public static void test() throws Exception {
        String address = "localhost:2181";
        CuratorFramework client = CuratorFrameworkFactory.newClient(address, new ExponentialBackoffRetry(1000, 3));
        
        try{
            client.start();
            
            String path = "/yongjiu2/yongjiu3/test5";
            
            //a. 创建永久性节点
            client.create()
              .creatingParentContainersIfNeeded()
              .withMode(CreateMode.PERSISTENT)
              .withACL(ZooDefs.Ids.OPEN_ACL_UNSAFE)
              .forPath(path, "hello, zk".getBytes());
            System.out.println("b");
            
            //b. 创建临时节点
            client.create().withMode(CreateMode.EPHEMERAL).forPath("/temptest5", "hello".getBytes());  
            
            System.out.println("c");
            //c.获取节点值
            byte[] buf = client.getData().forPath(path);
            System.out.println("get data path:"+path+", data:"+new String(buf));
            
            System.out.println("d");
            //d.设置节点值
            client.setData().inBackground().forPath(path, "ricky".getBytes());
            
            System.out.println("e");
            //e.checkExists
            Stat stat = client.checkExists().forPath(path);
            if(stat==null){
                System.out.println("exec create path:"+path);
            }else {
                System.out.println("exec getData");
            }
            
            System.out.println("f");
            //f.删除节点
            client.delete().deletingChildrenIfNeeded().forPath(path);
            
            byte[] buf2 = client.getData().forPath(path);
            System.out.println("get data path:"+path+", data:"+new String(buf2));
            
        }finally {
            if(client!=null)
                client.close();
        }
    }

示例二：临时节点不能有子节点、不能级联创建示例：

/**
     * 级联创建临时节点测试，结果会创建不成功，报错
     * @throws Exception
     */
    public static void test2() throws Exception {
        String address = "localhost:2181";
        CuratorFramework client = CuratorFrameworkFactory.newClient(address, new ExponentialBackoffRetry(1000, 3));
        
        try{
            client.start();
            
            String path = "/linshi";
            
            //b. 创建临时节点
            client.create().withMode(CreateMode.EPHEMERAL).forPath(path, "hello".getBytes());  
            
            byte[] buf = client.getData().forPath(path);
            System.out.println("get data path:"+path+", data:"+new String(buf));
            
            
            //Zookeeper创建临时节点的时候，不能创建级联的节点，下面的create会报错
            String path2 = "/linshi/test";
            //b. 创建临时节点
            client.create().withMode(CreateMode.EPHEMERAL).forPath(path2, "hello".getBytes());  
            
            
            //byte[] buf2 = client.getData().forPath(path2);
            //System.out.println("get data path:"+path2+", data:"+new String(buf2));
            
            
            TimeUnit.SECONDS.sleep(100 * 1000);
        }finally {
            if(client!=null)
                client.close();
        }
    }

示例三：3、临时节点何时失效演示（在会话结束时被移除）

/**
     * 临时节点什么时候失效？是在本次会话结束时
     * @throws Exception
     */
    public static void test3() throws Exception {
        String address = "localhost:2181";
        CuratorFramework client = CuratorFrameworkFactory.newClient(address, new ExponentialBackoffRetry(1000, 3));
        
        try{
            client.start();
            
            String path = "/linshi";
            
            //b. 创建临时节点
            client.create().withMode(CreateMode.EPHEMERAL).forPath(path, "hello".getBytes());  
            
            byte[] buf = client.getData().forPath(path);
            System.out.println("get data path:"+path+", data:"+new String(buf));
            
            TimeUnit.SECONDS.sleep(100 * 1000);
        }finally {
            if(client!=null)
                client.close();
        }
    }