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amitkumar02amitkumar02
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Leader election implementation using ZooKeeper
Leader election implementation using Apache ZooKeeper
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9 files changed

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‎.gitignore

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# virtual machine crash logs, see http://www.java.com/en/download/help/error_hotspot.xml
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hs_err_pid*
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*.lock
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.metadata
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RemoteSystemsTempFiles
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.settings

‎apache-zookeeper/leader-election/.classpath

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<?xml version="1.0" encoding="UTF-8"?>
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<classpath>
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<classpathentry kind="src" output="target/classes" path="src/main/java">
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<attributes>
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<attribute name="optional" value="true"/>
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<attribute name="maven.pomderived" value="true"/>
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</attributes>
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</classpathentry>
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<classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources">
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<attributes>
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<attribute name="maven.pomderived" value="true"/>
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</attributes>
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</classpathentry>
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<classpathentry kind="src" output="target/test-classes" path="src/test/java">
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<attributes>
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<attribute name="optional" value="true"/>
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<attribute name="maven.pomderived" value="true"/>
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</attributes>
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</classpathentry>
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<classpathentry excluding="**" kind="src" output="target/test-classes" path="src/test/resources">
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<attributes>
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<attribute name="maven.pomderived" value="true"/>
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</attributes>
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</classpathentry>
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<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER">
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<attributes>
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<attribute name="maven.pomderived" value="true"/>
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</attributes>
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</classpathentry>
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<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
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<attributes>
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<attribute name="maven.pomderived" value="true"/>
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</attributes>
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</classpathentry>
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<classpathentry kind="output" path="target/classes"/>
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</classpath>

‎apache-zookeeper/leader-election/.gitignore

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/target

‎apache-zookeeper/leader-election/.project

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<?xml version="1.0" encoding="UTF-8"?>
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<projectDescription>
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<name>leader-election</name>
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<comment></comment>
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<projects>
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</projects>
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<buildSpec>
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<buildCommand>
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<name>org.eclipse.jdt.core.javabuilder</name>
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<arguments>
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</arguments>
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</buildCommand>
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<buildCommand>
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<name>org.eclipse.m2e.core.maven2Builder</name>
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<arguments>
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</arguments>
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</buildCommand>
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</buildSpec>
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<natures>
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<nature>org.eclipse.jdt.core.javanature</nature>
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<nature>org.eclipse.m2e.core.maven2Nature</nature>
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</natures>
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</projectDescription>

‎apache-zookeeper/leader-election/pom.xml

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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.sts.allprogtutorials.apachezookeeper</groupId>
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<artifactId>leader-election</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<name>Leader Election</name>
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<dependencies>
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<dependency>
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<groupId>org.apache.zookeeper</groupId>
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<artifactId>zookeeper</artifactId>
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<version>3.4.6</version>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-compiler-plugin</artifactId>
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<version>3.3</version>
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<configuration>
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<source>1.7</source>
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<target>1.7</target>
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</configuration>
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</plugin>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-shade-plugin</artifactId>
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<version>2.3</version>
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<executions>
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<execution>
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<phase>package</phase>
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<goals>
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<goal>shade</goal>
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</goals>
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</execution>
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</executions>
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</plugin>
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</plugins>
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</build>
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</project>

‎apache-zookeeper/leader-election/src/main/java/com/sts/allprogtutorials/zk/leaderelection/main/LeaderElectionLauncher.java

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/**
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*
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*/
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package com.sts.allprogtutorials.zk.leaderelection.main;
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import java.io.IOException;
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import java.util.concurrent.ExecutionException;
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import java.util.concurrent.ExecutorService;
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import java.util.concurrent.Executors;
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import java.util.concurrent.Future;
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import org.apache.log4j.Logger;
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import com.sts.allprogtutorials.zk.leaderelection.nodes.ProcessNode;
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/**
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* @author Sain Technology Solutions
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*
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*/
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public class LeaderElectionLauncher {
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private static final Logger LOG = Logger.getLogger(LeaderElectionLauncher.class);
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public static void main(String[] args) throws IOException {
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final String zkURL = "10.127.128.56:2181";
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final ExecutorService service = Executors.newSingleThreadExecutor();
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final Future<?> status = service.submit(new ProcessNode(4, zkURL));
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try {
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status.get();
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} catch (InterruptedException | ExecutionException e) {
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LOG.fatal(e.getMessage(), e);
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service.shutdown();
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}
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}
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}

‎apache-zookeeper/leader-election/src/main/java/com/sts/allprogtutorials/zk/leaderelection/nodes/ProcessNode.java

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/**
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*
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*/
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package com.sts.allprogtutorials.zk.leaderelection.nodes;
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import java.io.IOException;
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import java.util.Collections;
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import java.util.List;
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import org.apache.log4j.Logger;
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import org.apache.zookeeper.WatchedEvent;
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import org.apache.zookeeper.Watcher;
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import org.apache.zookeeper.Watcher.Event.EventType;
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import com.sts.allprogtutorials.zk.utils.ZooKeeperService;
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/**
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* @author Sain Technology Solutions
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*
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*/
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public class ProcessNode implements Runnable{
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private static final Logger LOG = Logger.getLogger(ProcessNode.class);
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private static final String LEADER_ELECTION_ROOT_NODE = "/election";
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private static final String PROCESS_NODE_PREFIX = "/p_";
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private final int id;
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private final ZooKeeperService zooKeeperService;
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private String processNodePath;
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private String watchedNodePath;
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public ProcessNode(final int id, final String zkURL) throws IOException {
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this.id = id;
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zooKeeperService = new ZooKeeperService(zkURL, new ProcessNodeWatcher());
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}
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private void attemptForLeaderPosition() {
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final List<String> childNodePaths = zooKeeperService.getChildren(LEADER_ELECTION_ROOT_NODE, false);
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Collections.sort(childNodePaths);
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int index = childNodePaths.indexOf(processNodePath.substring(processNodePath.lastIndexOf('/') + 1));
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if(index == 0) {
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if(LOG.isInfoEnabled()) {
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LOG.info("[Process: " + id + "] I am the new leader!");
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}
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} else {
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final String watchedNodeShortPath = childNodePaths.get(index - 1);
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watchedNodePath = LEADER_ELECTION_ROOT_NODE + "/" + watchedNodeShortPath;
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if(LOG.isInfoEnabled()) {
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LOG.info("[Process: " + id + "] - Setting watch on node with path: " + watchedNodePath);
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}
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zooKeeperService.watchNode(watchedNodePath, true);
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}
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}
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@Override
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public void run() {
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System.out.println("Process with id: " + id + " has started!");
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final String rootNodePath = zooKeeperService.createNode(LEADER_ELECTION_ROOT_NODE, false, false);
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if(rootNodePath == null) {
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throw new IllegalStateException("Unable to create/access leader election root node with path: " + LEADER_ELECTION_ROOT_NODE);
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}
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processNodePath = zooKeeperService.createNode(rootNodePath + PROCESS_NODE_PREFIX, false, true);
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if(processNodePath == null) {
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throw new IllegalStateException("Unable to create/access process node with path: " + LEADER_ELECTION_ROOT_NODE);
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}
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if(LOG.isDebugEnabled()) {
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LOG.debug("[Process: " + id + "] Process node created with path: " + processNodePath);
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}
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attemptForLeaderPosition();
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}
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public class ProcessNodeWatcher implements Watcher{
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@Override
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public void process(WatchedEvent event) {
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if(LOG.isDebugEnabled()) {
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LOG.debug("[Process: " + id + "] Event received: " + event);
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}
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final EventType eventType = event.getType();
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if(EventType.NodeDeleted.equals(eventType)) {
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if(event.getPath().equalsIgnoreCase(watchedNodePath)) {
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attemptForLeaderPosition();
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}
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}
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}
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}
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}

‎apache-zookeeper/leader-election/src/main/java/com/sts/allprogtutorials/zk/utils/ZooKeeperService.java

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/**
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*
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*/
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package com.sts.allprogtutorials.zk.utils;
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import java.io.IOException;
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import java.util.List;
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import org.apache.zookeeper.CreateMode;
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import org.apache.zookeeper.KeeperException;
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import org.apache.zookeeper.ZooDefs.Ids;
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import org.apache.zookeeper.ZooKeeper;
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import org.apache.zookeeper.data.Stat;
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import com.sts.allprogtutorials.zk.leaderelection.nodes.ProcessNode.ProcessNodeWatcher;
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/**
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* @author Sain Technology Solutions
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*
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*/
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public class ZooKeeperService {
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private ZooKeeper zooKeeper;
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public ZooKeeperService(final String url, final ProcessNodeWatcher processNodeWatcher) throws IOException {
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zooKeeper = new ZooKeeper(url, 3000, processNodeWatcher);
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}
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public String createNode(final String node, final boolean watch, final boolean ephimeral) {
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String createdNodePath = null;
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try {
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final Stat nodeStat = zooKeeper.exists(node, watch);
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if(nodeStat == null) {
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createdNodePath = zooKeeper.create(node, new byte[0], Ids.OPEN_ACL_UNSAFE, (ephimeral ? CreateMode.EPHEMERAL_SEQUENTIAL : CreateMode.PERSISTENT));
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} else {
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createdNodePath = node;
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}
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} catch (KeeperException | InterruptedException e) {
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throw new IllegalStateException(e);
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}
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return createdNodePath;
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}
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public boolean watchNode(final String node, final boolean watch) {
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boolean watched = false;
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try {
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final Stat nodeStat = zooKeeper.exists(node, watch);
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if(nodeStat != null) {
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watched = true;
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}
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} catch (KeeperException | InterruptedException e) {
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throw new IllegalStateException(e);
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}
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return watched;
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}
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public List<String> getChildren(final String node, final boolean watch) {
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List<String> childNodes = null;
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try {
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childNodes = zooKeeper.getChildren(node, watch);
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} catch (KeeperException | InterruptedException e) {
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throw new IllegalStateException(e);
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}
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return childNodes;
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}
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}

‎apache-zookeeper/leader-election/src/main/resources/log4j.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
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<log4j:configuration debug="true"
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xmlns:log4j='http://jakarta.apache.org/log4j/'>
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<appender name="console" class="org.apache.log4j.ConsoleAppender">
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<layout class="org.apache.log4j.PatternLayout">
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<param name="ConversionPattern" value="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n" />
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</layout>
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</appender>
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<logger name="org.apache.zookeeper.ZooKeeper">
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<level value="warn" />
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</logger>
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<root>
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<level value="DEBUG" />
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<appender-ref ref="console" />
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</root>
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</log4j:configuration>

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