Initial commit

.gitignore

+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
\ No newline at end of file

.idea/.gitignore

+# Default ignored files
+/shelf/
+/workspace.xml

.idea/encodings.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="Encoding">
+    <file url="file://$PROJECT_DIR$/src/main/java" charset="UTF-8" />
+    <file url="file://$PROJECT_DIR$/src/main/resources" charset="UTF-8" />
+  </component>
+</project>
\ No newline at end of file

.idea/misc.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ExternalStorageConfigurationManager" enabled="true" />
+  <component name="MavenProjectsManager">
+    <option name="originalFiles">
+      <list>
+        <option value="$PROJECT_DIR$/pom.xml" />
+      </list>
+    </option>
+  </component>
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_17" default="true" project-jdk-name="17" project-jdk-type="JavaSDK">
+    <output url="file://$PROJECT_DIR$/out" />
+  </component>
+</project>
\ No newline at end of file

pom.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>org.example</groupId>
+    <artifactId>leader-election</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <properties>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.11.0</version>
+                <configuration>
+                    <source>17</source>
+                    <target>17</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.zookeeper</groupId>
+            <artifactId>zookeeper</artifactId>
+            <version>3.9.1</version>
+        </dependency>
+    </dependencies>
+</project>
\ No newline at end of file

src/main/java/LeaderElection.java

+import org.apache.zookeeper.*;
+import org.apache.zookeeper.data.Stat;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.List;
+
+public class LeaderElection implements Watcher {
+    private static final String address = "192.168.97.15:2181";
+    private static final int SESSION_TIMEOUT = 3000; //dead client
+    private static final String ELECTION_NAMESPACE = "/election";
+
+    private String currentZnodeName;
+    private ZooKeeper zooKeeper;
+
+
+    public static void main(String[] args) throws IOException, InterruptedException, KeeperException {
+        LeaderElection leaderElection = new LeaderElection();
+        leaderElection.connectToZookeeper();
+        leaderElection.volunteerForLeadership();
+        leaderElection.electLeader();
+        leaderElection.run();
+        leaderElection.close();
+        System.out.println("Successfully Closed");
+    }
+
+    public void volunteerForLeadership() throws InterruptedException, KeeperException {
+        String znodePrefix = ELECTION_NAMESPACE + "/c_";
+        String znodeFullPath = zooKeeper.create(znodePrefix, new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL_SEQUENTIAL);
+
+        System.out.println(znodeFullPath);
+        this.currentZnodeName = znodeFullPath.replace(ELECTION_NAMESPACE + "/", "");
+    }
+
+    public void electLeader() throws InterruptedException, KeeperException {
+        List<String> children = zooKeeper.getChildren(ELECTION_NAMESPACE, this);
+
+        Collections.sort(children);
+        String smallestChild = children.get(0); //the first element
+
+        if (smallestChild.equals(currentZnodeName)) {
+            System.out.println("I'm a leader");
+        } else {
+            System.out.println("I'm not a leader" + smallestChild + " is a leader.");
+        }
+
+    }
+
+    private void close() throws InterruptedException {
+        this.zooKeeper.close();
+    }
+
+    public void connectToZookeeper() throws IOException {
+        this.zooKeeper = new ZooKeeper(address, SESSION_TIMEOUT, this);
+    }
+
+    public void run() throws InterruptedException {
+        synchronized (zooKeeper) {
+            zooKeeper.wait();
+        }
+    }
+
+    @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 NodeChildrenChanged:
+                try {
+                    electLeader();
+                    System.out.println(ELECTION_NAMESPACE + " NodeChildrenChanged");
+                } catch (InterruptedException e) {
+                    throw new RuntimeException(e);
+                } catch (KeeperException e) {
+                    throw new RuntimeException(e);
+                }
+
+        }
+    }
+}