zookeeper的Java客戶端API

zookeeper作為一個分散式服務框架，主要用來解決分散式資料一致性問題，對多種語言提供了API。這裡主要記錄下JAVA客戶端API的使用。

 

1.建立會話

客戶端可以通過建立一個ZooKeeper例項來連線zookeeper伺服器

ZooKeeper的4個建構函式如下：

 

ZooKeeper(connectString, sessionTimeout, watcher);
ZooKeeper(connectString, sessionTimeout, watcher,canBeReadOnly);
ZooKeeper(connectString, sessionTimeout, watcher, sessionId, sessionPasswd);
ZooKeeper(connectString, sessionTimeout, watcher, sessionId, sessionPasswd, canBeReadOnly);

 

 

引數說明：

connectString: 連線字串 例如 "127.0.0.1:2181"

sessionTimeout: 會話超時時間 以毫秒為單位的整型值 在sessionTimeout時間內服務端與客戶端沒有有效的心跳檢測 則會話失效

watcher: 預設的事件通知處理器

sessionId: 會話ID

sessionPasswd: 會話祕鑰

canBeReadOnly: 是否是隻讀  

      

public class ZookeeperSampleTest implements Watcher {

    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    public static void main(String args[]) throws IOException, InterruptedException{
        ZooKeeper zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleTest());
        System.out.println(zk.getState());
        try {
            connectedSemaphore.await();
        } catch (Exception e) {
            // TODO: handle exception
        }
        Long sessionId = zk.getSessionId();
        byte[] password = zk.getSessionPasswd();
        zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleTest(),1L,"test".getBytes());
        zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleTest(),sessionId,password);
        Thread.sleep(Integer.MAX_VALUE);
        //System.out.println("ZooKeeper session established");
    }

    @Override
    public void process(WatchedEvent event) {
        // TODO Auto-generated method stub
        System.out.println("Receive watched event :" + event);
        if(event.getState()==KeeperState.SyncConnected){
            connectedSemaphore.countDown();
        }
    }

}

 

 

2.建立節點

建立節點的方式分為同步和非同步，建構函式如下：

 

zk.create(path, data, acl, createMode);
, data, acl, createMode, cb, ctx);

引數說明：

 

path: 建立節點的路徑 如：/zk-test

data[]: 位元組陣列，節點資料

acl: 許可權  

createMode: 節點型別  分為4種： 永續性節點，永續性有序節點，臨時節點，臨時有序節點

cb: 回撥函式 需要實現StringCallback介面

ctx: 上下文 一般用於回撥函式時候使用

 

public class ZookeeperSampleCreateTest implements Watcher {

    public static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    public static void main(String[] args) throws IOException, InterruptedException, KeeperException{
        ZooKeeper zk = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
        connectedSemaphore.await();
        /*同步的方式*/
        /*String path1 = zk.create("/zk-test-ephemeral-", "test-ephemeral".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        System.out.println("Success create node :" + path1);
        String path2 = zk.create("/zk-test-ephemeral-", "test-ephemeral-sequential".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
        System.out.println("Success create node :" + path2);*/

        /*非同步的方式*/
        zk.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,new IStringCallback(),"i am context");
        zk.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL,new IStringCallback(),"i am context");
        zk.create("/zk-test-ephemeral-", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL,new IStringCallback(),"i am context");
        Thread.sleep(Integer.MAX_VALUE);
    }

    @Override
    public void process(WatchedEvent event) {
        // TODO Auto-generated method stub
        if(KeeperState.SyncConnected == event.getState()){
            connectedSemaphore.countDown();
        }
    }
}

class IStringCallback implements AsyncCallback.StringCallback{

    @Override
    public void processResult(int rc, String path, Object ctx, String name) {
        // TODO Auto-generated method stub
        System.out.println("Create path result: [" + rc + "," + path + "," + ctx + ", real path name " + name);
    }

}

 

 

3.刪除節點

 

zk.delete(path,version);
zk.delete(path,version,cb,ctx);

引數說明：

 

path：節點路徑

version：版本號

cb: 回撥函式

ctx: 上下文

 

4.獲取子節點

getChildren有8個過載方法

 

              zk.getChildren(path, watch);
zk.getChildren(path, watcher);
zk.getChildren(path, watch, stat);
zk.getChildren(path, watcher, stat);
zk.getChildren(path, watch, cb, ctx);
zk.getChildren(path, watcher, cb, ctx);

其中 回撥函式有兩種  ChildrenCallback  Children2Callback

 

引數說明：

path：節點路徑

watch: boolean型別 如果為true 表示使用預設的Watcher 為false表示不需要Watcher

watcher: 通知處理器 在本次獲取子節點以後  一旦子節點有變化機會收到服務端傳來的通知

stat: 指定資料節點的節點狀態資訊，傳入一箇舊的stat物件，當執行方法後 stat會被伺服器響應的新stat替換

cb:回撥函式 有兩種型別 上面已經說過

ctx: 上下文

 5.獲取節點資料

獲取節點資料有4個過載方法

 

              zk.getData(path, watch, stat);
zk.getData(path, watcher, stat);
zk.getData(path, watch, cb, ctx);
zk.getData(path, watcher, cb, ctx);

引數說明：

 

path: 節點路徑

watch: boolean型別 如果為true 表示使用預設的Watcher 為false表示不需要Watcher

stat: 指定資料節點的節點狀態資訊，傳入一箇舊的stat物件，當執行方法後 stat會被伺服器響應的新stat替換

cb:回撥函式 有兩種型別 上面已經說過

ctx: 上下文

在獲取節點資料時候 如果註冊watcher 在節點資料傳送變化的時候會通知客戶端,當客戶端收到通知以後，如果想下次資料傳送變化再次收到通知，

需要重新註冊watcher,獲取子節點機制也如此

6.更新節點資料

更新節點資料也分為同步非同步兩個方法

 

zk.setData(path, data, version);
zk.setData(path, data, version, cb, ctx);

引數說明：同上

 

 

public class ZookeeperSampleGetDataTest implements Watcher {

    public static CountDownLatch connectedSemaphore = new CountDownLatch(1);

    public static Stat stat = new Stat();

    public static ZooKeeper zk = null;

    public static void main(String[] args) throws IOException, KeeperException, InterruptedException{
        String path = "/zk-test";
        zk = new ZooKeeper("192.168.1.138:2181", 5000, new ZookeeperSampleGetDataTest());
        connectedSemaphore.await();

        //獲取子節點
        /*zk.delete(path, 0);
        zk.create(path, "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
        zk.create(path+"/c1", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        //同步方法獲取children
        //List<String> childs = zk.getChildren(path, true);
        //System.out.println(childs);
        //非同步方法獲取children
        zk.getChildren(path, true, new IChildren2Callback(), null);

        zk.create(path+"/c2", "".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
        Thread.sleep(Integer.MAX_VALUE);*/
        //獲取節點資料
        zk.delete(path, 0);
        zk.create(path, "123".getBytes(), Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);

        System.out.println(new String(zk.getData(path, true, stat)));
        /** czxid: 建立該節點的事務ID  mzxid: 更新該節點的事務ID  version： 資料版本*/
        System.out.println("Czxid: " + stat.getCzxid() + "Mzxid: " + stat.getMzxid() + "Version: " + stat.getVersion());

        zk.setData(path, "123".getBytes(), -1);

        Thread.sleep(Integer.MAX_VALUE);
    }


    @Override
    public void process(WatchedEvent event) {
        // TODO Auto-generated method stub
        if(KeeperState.SyncConnected==event.getState()){
            if(EventType.None==event.getType() && null==event.getPath()){
                connectedSemaphore.countDown();
            }else if(event.getType()==EventType.NodeChildrenChanged){
                try {
                    System.out.println("Get Child :" + zk.getChildren(event.getPath(), true));
                } catch (KeeperException | InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }else if(event.getType()==EventType.NodeDataChanged){
                try {
                    System.out.println(new String(zk.getData(event.getPath(), true, stat)));
                    System.out.println("Czxid: " + stat.getCzxid() + "Mzxid: " + stat.getMzxid() + "Version: " + stat.getVersion());
                } catch (KeeperException | InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
    }
}

class IChildren2Callback implements AsyncCallback.Children2Callback{

    @Override
    public void processResult(int rc, String path, Object ctx,
            List<String> childrens, Stat stat) {
        // TODO Auto-generated method stub
        System.out.println("Get Children znode result: [response code: " + rc + ", param path: " + path + ", ctx " + ctx
                + ", childrens :" +  childrens + ", stat: " + stat);
    }

}

其中更新節點資料 版本version問題 -1表示基於資料的最新版本更新 這裡可以作為分散式鎖的一個思路 如果客戶端參入的version不是資料最新版本則會更新失敗

 

比如目前節點"/zk-test"的資料版本為 2 而某個客戶端嘗試 執行 setData("/zk-test","test".getBytes(),1) 由於傳入version為1 < 伺服器目前版本2 這樣就會更新失敗

7.檢測節點是否存在

 

              zk.exists(path, watch);
zk.exists(path, watcher);
zk.exists(path, watch, cb, ctx);
zk.exists(path, watcher, cb, ctx);

如果判斷節點是否存在是 註冊watcher 會對節點是否存在進行監聽--建立節點，刪除節點，節點資料更新都會通知客戶端

 

8.許可權控制

zookeeper提供了ACL的許可權控制機制，簡單來說就是通過控制zookeeper伺服器上資料節點的ACL，來控制客戶端對節點的訪問許可權

 

addAuthInfo(String scheme,byte[] auth);

引數說明：

 

scheme: 許可權控制模式 分為： world ,auth,digest,ip和super

auth: 具體的許可權資訊  類似於shiro的許可權字串

如下程式碼：

 

<span style="white-space:pre;">     </span>ZooKeeper zk1 = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
        zk1.addAuthInfo("digest", "test:true".getBytes());
        zk1.create("/zk-test-auth", "123".getBytes(), Ids.CREATOR_ALL_ACL, CreateMode.EPHEMERAL);
        ZooKeeper zk2 = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
        zk2.addAuthInfo("digest", "test:true".getBytes());
        System.out.println(new String(zk2.getData("/zk-test-auth", false, null)));
        ZooKeeper zk3 = new ZooKeeper("192.168.1.138:2181",5000,new ZookeeperSampleCreateTest());
        zk3.addAuthInfo("digest", "test:false".getBytes());
        zk3.getData("/zk-test-auth", false, null);

zk2設定了正確的許可權 所以可以獲取到節點資料  zk3則會拋異常

 

 org.apache.zookeeper.KeeperException$NoAuthException: KeeperErrorCode = NoAuth for /zk-test-auth