Java zookeeper example 2017-01-22 04:13

In this page I will show you how to use zookeeper as a configuration service. I use a standalone zookeeper for the demonstration. If you want to build a high availability configuration service click here for more detail.

1. Download and install zookeeper.

   Download zookeeper from here and unzip it. For to start it you need rename the zoo_sample.cfg to zoo.cfg.

   wget http://apache.claz.org/zookeeper/zookeeper-3.4.9/zookeeper-3.4.9.tar.gz
   tar -vxf zookeeper-3.4.9.tar.gz
   cd zookeeper-3.4.9/conf
   cp zoo_sample.cfg zoo.cfg

2. Start zookeeper in standalone mode.

   ../bin/zkServer.sh start

   If zookeeper start successfully the output is like following.

   ZooKeeper JMX enabled by default
   Using config: /root/zookeeper-3.4.9/bin/../conf/zoo.cfg
   Starting zookeeper ... STARTED

3. Use java api read and write configuration The pom file is like following.

   <dependency>
       <groupId>org.apache.zookeeper</groupId>
       <artifactId>zookeeper</artifactId>
       <version>3.4.9</version>
   </dependency>

   We use ZkUtil to create, update and read configuration from zookeeper.

   public class ZkUtil {
       private static ZooKeeper zk;
   
       private ZkUtil() {
       }
   
       static {
           try {
               //my host and port is :10.232.56.19:2181 , change host and port to yours
               zk = new ZooKeeper("10.232.56.19:2181", 3000, new Watcher() {
                   public void process(WatchedEvent event) {
                       switch (event.getType()) {
                           case NodeDeleted:
                               System.out.println("node delete");// do your logic here
                               break;
                           case NodeCreated:
                               System.out.println("node created");// do your logic here
                               break;
                           case NodeDataChanged:
                               System.out.println("node changed");// do your logic here
                               break;
                           case NodeChildrenChanged:
                               System.out.println("node children changed");// do your logic here
                               break;
                           default:
                               break;
                       }
                   }
               });
           } catch (Exception e) {
               e.printStackTrace();
           }
       }
   
       public static String getData(String path) throws Exception {
           byte[] data = zk.getData(path, true, zk.exists(path, true));
           return new String(data);
       }
   
       public static void createData(String path, String value) throws Exception {
           if (zk.exists(path, true) != null) {
               return;
           }
           zk.create(path, value.getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
       }
   
       public static void updateDate(String path, String value) throws Exception {
           zk.setData(path, value.getBytes(), zk.exists(path, true).getVersion());
       }
   }

   The code of client.

   public class ZkTest {
       public static void main(String[] args) throws Exception {
           ZkUtil.createData("/test","value");
           String data = ZkUtil.getData("/test");
           System.out.println(data);
           ZkUtil.updateDate("/test","new value1");
           String newData = ZkUtil.getData("/test");
           System.out.println(newData);
       }
   }

The one of the most important advantages of using zookeeper is change configurations dynamically and read them without restart server