Watchers, Triggers and Introduction to Failure Detection

Readme.md

@@ -6,6 +6,7 @@
 * Zookeeper Server and Client
 * Zookeeper Client Threading Model & Zookeeper Java API
 * Leader Election Implementation
+* Watchers, Triggers and Introduction to Failure Detection
 
 
 *Useful links*

src/main/java/WatchersAndTriggers.java

+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.WatchedEvent;
+import org.apache.zookeeper.Watcher;
+import org.apache.zookeeper.ZooKeeper;
+import org.apache.zookeeper.data.Stat;
+
+import java.io.IOException;
+import java.util.List;
+
+public class WatchersAndTriggers implements Watcher {
+
+    private static final String address = "172.29.3.101:2181";
+
+    private static final int SESSION_TIMEOUT = 3000; //dead client
+    private static final String TargetZnode = "/target_znode";
+
+    private ZooKeeper zooKeeper;
+
+    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
+        WatchersAndTriggers watchersAndTriggers = new WatchersAndTriggers();
+
+        watchersAndTriggers.connectToZookeeper();
+        watchersAndTriggers.testWatcher();
+
+        watchersAndTriggers.run();
+        watchersAndTriggers.close();
+
+    }
+
+    private void close() throws InterruptedException {
+        this.zooKeeper.close();
+    }
+
+    private void run() throws InterruptedException {
+        synchronized (zooKeeper) {
+            this.zooKeeper.wait();
+        }
+    }
+
+    private void connectToZookeeper() throws IOException {
+        this.zooKeeper = new ZooKeeper(address, SESSION_TIMEOUT, this);
+    }
+
+    public void testWatcher() throws InterruptedException, KeeperException {
+        Stat stat = zooKeeper.exists(TargetZnode, this);
+        if (stat == null) {
+            System.out.println(TargetZnode + " not exist");
+            return;
+        }
+        byte[] data = zooKeeper.getData(TargetZnode, this, stat);
+        List<String> children = zooKeeper.getChildren(TargetZnode, this);
+
+        System.out.println("Data " + new String(data) + "children " + children);
+    }
+
+    @Override
+    public void process(WatchedEvent watchedEvent) {
+        switch (watchedEvent.getType()) {
+            case None:
+                if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
+                    System.out.println("Successfully connected to Zookeeper");
+                } else if (watchedEvent.getState() == Event.KeeperState.Disconnected) {
+                    synchronized (zooKeeper) {
+                        System.out.println("Disconnected from Zookeeper");
+                        zooKeeper.notifyAll();
+                    }
+                } else if (watchedEvent.getState() == Event.KeeperState.Closed) {
+                    System.out.println("Closed Successfully");
+                }
+            case NodeCreated:
+                System.out.println(TargetZnode + " Created");
+                break;
+            case NodeDeleted:
+                System.out.println(TargetZnode + " Deleted");
+                break;
+            case NodeDataChanged:
+                System.out.println(TargetZnode + " DataChanged");
+                break;
+            case NodeChildrenChanged:
+                System.out.println(TargetZnode + " ChildrenChanged");
+                break;
+        }
+        try {
+            testWatcher();
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        } catch (KeeperException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}