讀《分布式一致性原理》JAVA用戶端API操作

標籤：主程   技術   connect   通知   latch   current   over   執行個體   圖片   

建立會話

用戶端可以通過建立一個Zookeeper執行個體來串連伺服器。4種構造方法如下

ZooKeeper(connectString, sessionTimeout, watcher)；ZooKeeper(String connectString, int sessionTimeout, Watcher watcher, boolean canBeReadOnly) ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,long sessionId, byte[] sessionPasswd)；ZooKeeper(String connectString, int sessionTimeout, Watcher watcher,long sessionId, byte[] sessionPasswd, boolean canBeReadOnly)

 

 

注意，zookeeper用戶端和服務端會話建立是一個非同步過程，也是就是說在程式中構造zookeeper方法初始化方法執行完後

會立即返回，在大多數情況下此時並沒有真正的建立一個可用的會話，此時會話正處於CONnectioning狀態。當真正的會話建立後

服務端會向用戶端發送一個通知，用戶端在擷取這個通知後會話才真正的建立。

package session;import java.io.IOException;import java.util.concurrent.CountDownLatch;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher;import org.apache.zookeeper.ZooKeeper;import org.apache.zookeeper.Watcher.Event.KeeperState;public class CreateZookeeper implements Watcher {    private static CountDownLatch connectedSemaphore = new CountDownLatch(1);        @Override    public void process(WatchedEvent event) {        System.out.println("receive watched event:"+event);        if (KeeperState.SyncConnected==event.getState()) {            connectedSemaphore.countDown();        }            }    public static void main(String[] args) throws IOException {        ZooKeeper zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper());                System.out.println(zooKeeper.getState());                try {            connectedSemaphore.await();        } catch (InterruptedException e) {}            System.out.println("zookeeper session established");                    }    }

程式運行結果如下：

CreateZookeeper類實現了Watcher介面重寫了process方法，該方法負責處理來自zookeeper服務端的通知。在

收到來自服務端的synconncted事件後，解除了主程式中的CountDownLatch等待阻塞。至此用戶端工作階段建立完成。

 

 建立一個複用sessionId和sessionPasswd的執行個體

package session;import java.io.IOException;import java.util.concurrent.CountDownLatch;import org.apache.zookeeper.WatchedEvent;import org.apache.zookeeper.Watcher;import org.apache.zookeeper.ZooKeeper;import org.apache.zookeeper.Watcher.Event.KeeperState;public class CreateZookeeper2 implements Watcher {public static CountDownLatch connectedSemaphore = new CountDownLatch(1);@Overridepublic void process(WatchedEvent event) {    System.out.println("receive watched event:"+event);    if (KeeperState.SyncConnected==event.getState()) {        connectedSemaphore.countDown();    }    }public static void main(String[] args) throws IOException, InterruptedException {    ZooKeeper zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper());    connectedSemaphore.await();    long sessionId = zooKeeper.getSessionId();    byte[] sessionPasswd = zooKeeper.getSessionPasswd();        //複用sessionId和sessionPasswd     zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper(),1l,"test".getBytes());          zooKeeper = new ZooKeeper("192.168.64.60", 5000, new CreateZookeeper(),sessionId,sessionPasswd);          Thread.sleep(Integer.MAX_VALUE);}}

我們可以看出，第一次使用錯誤的id和pw服務端返回“EXpired”事件，而第二次使用正確的id和pw則重新串連上。

讀《分布式一致性原理》JAVA用戶端API操作