Leader Election

.idea/artifacts/zookeeper_jar.xml

+<component name="ArtifactManager">
+  <artifact type="jar" name="zookeeper:jar">
+    <output-path>$PROJECT_DIR$/out/artifacts/zookeeper_jar</output-path>
+    <root id="archive" name="zookeeper.jar">
+      <element id="module-output" name="zookeeper" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-common/4.1.94.Final/netty-common-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-resolver/4.1.94.Final/netty-resolver-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-tcnative-boringssl-static/2.0.61.Final/netty-tcnative-boringssl-static-2.0.61.Final-windows-x86_64.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/org/apache/yetus/audience-annotations/0.12.0/audience-annotations-0.12.0.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-tcnative-boringssl-static/2.0.61.Final/netty-tcnative-boringssl-static-2.0.61.Final-osx-aarch_64.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-tcnative-boringssl-static/2.0.61.Final/netty-tcnative-boringssl-static-2.0.61.Final-linux-x86_64.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-tcnative-boringssl-static/2.0.61.Final/netty-tcnative-boringssl-static-2.0.61.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/org/apache/zookeeper/zookeeper-jute/3.9.1/zookeeper-jute-3.9.1.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/org/slf4j/slf4j-api/1.7.30/slf4j-api-1.7.30.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/commons-io/commons-io/2.11.0/commons-io-2.11.0.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-tcnative-classes/2.0.61.Final/netty-tcnative-classes-2.0.61.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/ch/qos/logback/logback-core/1.2.10/logback-core-1.2.10.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-buffer/4.1.94.Final/netty-buffer-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/ch/qos/logback/logback-classic/1.2.10/logback-classic-1.2.10.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-transport/4.1.94.Final/netty-transport-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/org/apache/zookeeper/zookeeper/3.9.1/zookeeper-3.9.1.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-codec/4.1.94.Final/netty-codec-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-transport-native-unix-common/4.1.94.Final/netty-transport-native-unix-common-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-transport-classes-epoll/4.1.94.Final/netty-transport-classes-epoll-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-tcnative-boringssl-static/2.0.61.Final/netty-tcnative-boringssl-static-2.0.61.Final-linux-aarch_64.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-handler/4.1.94.Final/netty-handler-4.1.94.Final.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-tcnative-boringssl-static/2.0.61.Final/netty-tcnative-boringssl-static-2.0.61.Final-osx-x86_64.jar" path-in-jar="/" />
+      <element id="extracted-dir" path="$MAVEN_REPOSITORY$/io/netty/netty-transport-native-epoll/4.1.94.Final/netty-transport-native-epoll-4.1.94.Final-linux-x86_64.jar" path-in-jar="/" />
+    </root>
+  </artifact>
+</component>
\ No newline at end of file

.idea/misc.xml

@@ -8,7 +8,7 @@
       </list>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="17" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_8" default="true" project-jdk-name="1.8" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>
 </project>
\ No newline at end of file

.idea/workspace.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
+  <component name="ArtifactsWorkspaceSettings">
+    <artifacts-to-build>
+      <artifact name="zookeeper:jar" />
+    </artifacts-to-build>
+  </component>
   <component name="AutoImportSettings">
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
@@ -34,7 +39,11 @@
   "keyToString": {
     "RunOnceActivity.OpenProjectViewOnStart": "true",
     "RunOnceActivity.ShowReadmeOnStart": "true",
-    "SHARE_PROJECT_CONFIGURATION_FILES": "true"
+    "SHARE_PROJECT_CONFIGURATION_FILES": "true",
+    "last_opened_file_path": "C:/Users/Abdullah/Desktop/Java/zookeeper",
+    "project.structure.last.edited": "Artifacts",
+    "project.structure.proportion": "0.0",
+    "project.structure.side.proportion": "0.0"
   }
 }]]></component>
   <component name="SpellCheckerSettings" RuntimeDictionaries="0" Folders="0" CustomDictionaries="0" DefaultDictionary="application-level" UseSingleDictionary="true" transferred="true" />

src/main/java/org/example/LeaderElection.java

@@ -2,29 +2,64 @@ package org.example;
 
 import org.apache.zookeeper.*;
 import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.data.Stat;
 
 import java.io.IOException;
-import java.net.ConnectException;
-import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
 
 public class LeaderElection implements Watcher {
-    private static final String address = "192.168.56.115:2181";
-    private static final int SESSION_TIMEOUT = 3000; //dead client
+    private static final String ADDRESS = "192.168.56.115:2181";
+    private static final int SESSION_TIMEOUT = 3000;
+    private static final String ELECTION_NAMESPACE = "/election";
+    private String currentZnodeName;
+    private String leader;
     private ZooKeeper zooKeeper = null;
 
+    private void volunteerForLeadership() throws InterruptedException, KeeperException {
+        String znodePrefix = ELECTION_NAMESPACE + "/c_";
+        String path = zooKeeper.create(znodePrefix, new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
+        this.currentZnodeName = path.replace(ELECTION_NAMESPACE + "/", "");
+        System.out.println("Created znode: " + path);
+    }
+
+    private void electLeader() throws InterruptedException, KeeperException {
+        List<String> children = zooKeeper.getChildren(ELECTION_NAMESPACE, false);
+        Collections.sort(children);
+        leader = children.get(0);
+        if (currentZnodeName.equals(leader)) {
+            System.out.println("I'm the leader");
+            //set data in leader Znode.
+            setLeaderData(currentZnodeName);
+        } else {
+            System.out.println("I'm not the leader, the leader is " + leader);
+            // Set a watch on the znode with one less sequence number
+            int currentZnodeIndex = children.indexOf(currentZnodeName);
+            String previousZnode = ELECTION_NAMESPACE + "/" + children.get(currentZnodeIndex - 1);
+            zooKeeper.exists(previousZnode, this);
+        }
+    }
+
+    private void setLeaderData(String znodeName) {
+        String znodePath = ELECTION_NAMESPACE + "/" + znodeName;
+        try {
+            zooKeeper.setData(znodePath, ("The leader is " + znodeName).getBytes(), -1);
+        } catch (KeeperException | InterruptedException e) {
+            throw new RuntimeException("Error setting leader data", e);
+        }
+    }
+
 
     public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
         LeaderElection leaderElection = new LeaderElection();
         leaderElection.connectToZookeeper();
+        leaderElection.volunteerForLeadership();
+        leaderElection.electLeader();
         leaderElection.run();
     }
 
     public void connectToZookeeper() throws IOException {
-
-        this.zooKeeper = new ZooKeeper(address, SESSION_TIMEOUT, this);
-
+        this.zooKeeper = new ZooKeeper(ADDRESS, SESSION_TIMEOUT, this);
     }
 
     public void run() throws InterruptedException {
@@ -38,20 +73,71 @@ public class LeaderElection implements Watcher {
     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.Expired) {
-                    System.out.println("ZooKeeper session expired. Shutting down the program.");
-                    synchronized (zooKeeper) {
-                        zooKeeper.notifyAll();
-                    }
-                } else if (watchedEvent.getState() == Event.KeeperState.Disconnected) {
-                    System.out.println("Disconnected from ZooKeeper. Shutting down the program.");
-                    synchronized (zooKeeper) {
-                        zooKeeper.notifyAll();
-                    }
-                }
+                handleNoneEvent(watchedEvent);
+                break;
+            case NodeDeleted:
+                handleNodeDeletedEvent(watchedEvent);
+                break;
+            case NodeDataChanged:
+                handleNodeDataChangedEvent(watchedEvent);
                 break;
         }
     }
+
+    private void handleNodeDeletedEvent(WatchedEvent watchedEvent) {
+        String deletedZnodePath = watchedEvent.getPath();
+        System.out.println("Znode deleted: " + deletedZnodePath);
+
+        // Check if the deleted znode is the leader
+        if (deletedZnodePath.equals(ELECTION_NAMESPACE + "/" + leader)) {
+            System.out.println("The deleted znode was the leader. Re-electing leader...");
+
+            try {
+                // Re-elect leader
+                electLeader();
+            } catch (InterruptedException | KeeperException e) {
+                throw new RuntimeException("Error re-electing leader", e);
+            }
+        }
+    }
+
+
+    private void handleNodeDataChangedEvent(WatchedEvent watchedEvent)  {
+        String znodePath = watchedEvent.getPath();
+        System.out.println("Znode data changed: " + znodePath);
+
+        byte[] znodePathBytes = new byte[]{};
+        try {
+            //get data of the znode which changed its data
+            znodePathBytes = zooKeeper.getData(znodePath, false, null);
+
+            // Set the data of the current znode to the combined data
+            zooKeeper.setData(ELECTION_NAMESPACE+"/"+currentZnodeName, znodePathBytes, -1);
+
+            String data = new String(znodePathBytes);
+            System.out.println(data);
+
+        } catch (KeeperException e) {
+            throw new RuntimeException(e);
+        } catch (InterruptedException e) {
+            throw new RuntimeException(e);
+        }
+
+    }
+
+    private void handleNoneEvent(WatchedEvent watchedEvent) {
+        if (watchedEvent.getState() == Event.KeeperState.SyncConnected) {
+            System.out.println("Successfully connected to ZooKeeper");
+        } else if (watchedEvent.getState() == Event.KeeperState.Expired) {
+            System.out.println("ZooKeeper session expired. Shutting down the program.");
+            synchronized (zooKeeper) {
+                zooKeeper.notifyAll();
+            }
+        } else if (watchedEvent.getState() == Event.KeeperState.Disconnected) {
+            System.out.println("Disconnected from ZooKeeper. Shutting down the program.");
+            synchronized (zooKeeper) {
+                zooKeeper.notifyAll();
+            }
+        }
+    }
 }

src/main/resources/META-INF/MANIFEST.MF

+Manifest-Version: 1.0
+Main-Class: org.example.LeaderElection
+