zk server启动

例子是client创建一个session
需要确保zkServer开启了，即

Paste_Image.png

配置参考
https://zookeeper.apache.org/doc/trunk/zookeeperStarted.html

demo

demo实现
1.客户端创建zk链接
2.创建，修改，删除znode
3.获取子节点列表，节点内容
4.watcher的使用

import org.apache.zookeeper.AsyncCallback;
import org.apache.zookeeper.CreateMode;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooDefs;
import org.apache.zookeeper.ZooKeeper;
import org.apache.zookeeper.data.Stat;

import java.util.List;
import java.util.concurrent.CountDownLatch;

public class Main {
    private static CountDownLatch countDownLatch = new CountDownLatch(1);

    private static ZooKeeper zk;

    private static final String ZOOKEEPER_ZNODE_NAME = "zookeeper";

    public static void startZK() throws Exception {
        System.out.println("startZK----------------------");
        //确保server确实已经开启了，这里是创建client到server的session
        zk = new ZooKeeper("127.0.0.1:2181", 20000,
                new Watcher() {
                    @Override
                    public void process(WatchedEvent watchedEvent) {
                        System.out.println("process " + watchedEvent);
                        if (watchedEvent.getState() ==
                                Event.KeeperState.SyncConnected) {
                            countDownLatch.countDown();
                        }
                    }
                });
        try {
            countDownLatch.await();
        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println("state is " + zk.getState());
        System.out.println("zk session begin");
    }

    //同步创建临时节点
    public static void syncCreateNode() {
        System.out.println("syncCreateNode----------------------");
        try {
            String path1 = zk.create("/test1", "znode1".getBytes(),
                    ZooDefs.Ids.OPEN_ACL_UNSAFE,
                    CreateMode.EPHEMERAL);
            String path2 = zk.create("/test2", "znode2".getBytes(),
                    ZooDefs.Ids.OPEN_ACL_UNSAFE,
                    CreateMode.EPHEMERAL);
            System.out.println("path1 = " + path1);
            System.out.println("path2 = " + path2);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //异步创建临时节点，这里等待它执行完看processResult
    public static void asnycCreateNode() throws Exception {
        System.out.println("asnycCreateNode----------------------");
        zk.create("/test3", "znode3".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,
                CreateMode.EPHEMERAL, new IStringCallBack(), "context");
        Thread.sleep(2000);
    }
    static class IStringCallBack implements AsyncCallback.StringCallback {
        @Override
        public void processResult(int rc, String path, Object ctx,
                String name) {
            System.out.println(
                    "Create path result " + rc + " " + path + " " + ctx + " " +
                            name);
        }
    }

    public static void clear() throws Exception {
        List<String> childList = zk.getChildren("/", false);
        for(String s : childList) {
            if(s.equals(ZOOKEEPER_ZNODE_NAME))
                continue;
            zk.delete("/" + s, -1);
        }
    }

    //获取子节点列表，在子节点列表变更时触发
    public static void getChildren() throws Exception {
        System.out.println("getChildren----------------------");
        List<String> childList = zk.getChildren("/", new Watcher() {
            @Override
            //这个znode的子节点变化的时候会收到通知
            public void process(WatchedEvent watchedEvent) {
                System.out.println("getChildren " + watchedEvent);
            }
        });
        System.out.println("childList " + childList);
    }

    //获取数据，注册监听器，在znode内容被改变时触发
    public static void getData() throws Exception {
        System.out.println("getData----------------------");
        String ans1 = new String(zk.getData("/test1", false, null));
        String ans2 = new String(zk.getData("/test2", new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                System.out.println("getData " + watchedEvent);
            }
        }, null));
        System.out.println("znode /test1 content is " + ans1);
        System.out.println("znode /test2 content is " + ans2);
    }

    //更新内容，会触发对应znode的watch事件
    public static void setData() throws Exception {
        System.out.println("setData----------------------");
        String data = "zNode22";
        zk.setData("/test2", data.getBytes(), -1);
        String ans2 = new String(zk.getData("/test2", false, null));
        System.out.println("setData to " + ans2);
    }

    //节点是否存在，watch监听节点的创建，删除以及更新
    public static void exists() throws Exception {
        System.out.println("exists----------------------");
        Stat stat = zk.exists("/test2", new Watcher() {
            @Override
            public void process(WatchedEvent watchedEvent) {
                System.out.println("exists " + watchedEvent);
            }
        });
        System.out.println("stat is " + stat);
    }

    public static void delete() throws Exception {
        System.out.println("delete----------------------");
        zk.delete("/test2", -1);
        zk.delete("/test1", -1);
    }

    public static void main(String[] args) throws Exception {
        startZK();
        clear();
        syncCreateNode();
        asnycCreateNode();
        getChildren();
        exists();
        getData();
        setData();
        delete();
    }
}

输出为

startZK----------------------
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
process WatchedEvent state:SyncConnected type:None path:null
state is CONNECTED
zk session begin
syncCreateNode----------------------
path1 = /test1
path2 = /test2
asnycCreateNode----------------------
Create path result 0 /test3 context /test3
getChildren----------------------
childList [test2, test3, zookeeper, test1]
exists----------------------
stat is 166,166,1489033819553,1489033819553,0,0,0,97584724014858276,6,0,166

getData----------------------
znode /test1 content is znode1
znode /test2 content is znode2
setData----------------------
getData WatchedEvent state:SyncConnected type:NodeDataChanged path:/test2
exists WatchedEvent state:SyncConnected type:NodeDataChanged path:/test2
setData to zNode22
delete----------------------
getChildren WatchedEvent state:SyncConnected type:NodeChildrenChanged path:/

Process finished with exit code 0

说明

watcher是一次性的，只触发一次,参见refer，并不是一直监听。不是很理解这样做的原因
watcher用于监听各种事件，包括子节点的变动，节点的删除，创建，以及内容(实质是版本)的改变
“zookeeper”是默认存在的一个znode

refer

http://www.cnblogs.com/zhwbqd/p/3969161.html
(API)https://zookeeper.apache.org/doc/r3.4.6/api/org/apache/zookeeper/ZooKeeper.html