Pupli – Page 141

RabbitMQ Exchange Types

July 17, 2017

Direct

Fanout

Topic

Headers

References
https://lostechies.com/derekgreer/2012/03/28/rabbitmq-for-windows-exchange-types/

Fair dispatch in RabbitMQ

July 16, 2017

Server : Consumer

public class Main {

    public static void main(String[] args) throws IOException, TimeoutException {
        String queueName = "queue2";

        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();

        Channel channel = connection.createChannel();

        channel.queueDeclare(queueName, true, false, false, null);
        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

        channel.basicQos(1);

        Consumer consumer = new DefaultConsumer(channel) {
            @Override
            public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
                String message=new String(body,"UTF-8");

                try {
                    doWork(message);
                }
                catch (Exception ex)
                {
                    ex.printStackTrace();
                }
                finally {
                    channel.basicAck(envelope.getDeliveryTag(),false);
                }
            }
        };

        channel.basicConsume(queueName,false,consumer);
    }

    public static void doWork(String message) throws InterruptedException {
        System.out.println(" [x] Received '" + message + "'");

        int sleepTime=new Random().nextInt(2000);

        Thread.sleep(sleepTime);
    }
}

References
https://pupli.net/2017/07/16/work-queues-sample-in-rabbitmq/
https://www.rabbitmq.com/tutorials/tutorial-two-java.html

Message durability in RabbitMQ

July 16, 2017

Server : Consumer

public class Main {

    public static void main(String[] args) throws IOException, TimeoutException {
        String queueName = "queue2";

        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();

        Channel channel = connection.createChannel();

        channel.queueDeclare(queueName, true, false, false, null);
        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

        channel.basicQos(1);

        Consumer consumer = new DefaultConsumer(channel) {
            @Override
            public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
                String message=new String(body,"UTF-8");

                try {
                    doWork(message);
                }
                catch (Exception ex)
                {
                    ex.printStackTrace();
                }
                finally {
                    channel.basicAck(envelope.getDeliveryTag(),false);
                }
            }
        };

        channel.basicConsume(queueName,false,consumer);
    }

    public static void doWork(String message) throws InterruptedException {
        System.out.println(" [x] Received '" + message + "'");

        int sleepTime=new Random().nextInt(2000);

        Thread.sleep(sleepTime);
    }
}

Client : Producer

public class Main {

    public static void main(String[] args) throws IOException, TimeoutException, InterruptedException {

        String queueName = "queue2";

        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        channel.queueDeclare(queueName, true, false, false, null);

        int count = 0;

        while (count < 100) {

            Date date = new Date();

            String message = String.format("%d : %s", count, date.toString());

            channel.basicPublish("", queueName, MessageProperties.PERSISTENT_TEXT_PLAIN,
                    message.getBytes("UTF-8"));
            System.out.println(String.format(" [x] Sent %s", message));

            Thread.sleep(1000);
            count++;
        }
    }
}

References
https://pupli.net/2017/07/16/work-queues-sample-in-rabbitmq/
https://www.rabbitmq.com/tutorials/tutorial-two-java.html

Message acknowledgment in RabbitMQ

July 16, 2017

Server : Consumer

public class Main {

    public static void main(String[] args) throws IOException, TimeoutException {
        String queueName = "queue2";

        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();

        Channel channel = connection.createChannel();

        channel.queueDeclare(queueName, true, false, false, null);
        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

        channel.basicQos(1);

        Consumer consumer = new DefaultConsumer(channel) {
            @Override
            public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
                String message=new String(body,"UTF-8");

                try {
                    doWork(message);
                }
                catch (Exception ex)
                {
                    ex.printStackTrace();
                }
                finally {
                    channel.basicAck(envelope.getDeliveryTag(),false);
                }
            }
        };

        channel.basicConsume(queueName,false,consumer);
    }

    public static void doWork(String message) throws InterruptedException {
        System.out.println(" [x] Received '" + message + "'");

        int sleepTime=new Random().nextInt(2000);

        Thread.sleep(sleepTime);
    }
}

References
https://pupli.net/2017/07/16/work-queues-sample-in-rabbitmq/
https://www.rabbitmq.com/tutorials/tutorial-two-java.html

Round-robin dispatching in RabbitMQ

July 16, 2017

By default, RabbitMQ will send each message to the next consumer, in sequence. On average every consumer will get the same number of messages. This way of distributing messages is called round-robin.

References
https://pupli.net/2017/07/16/work-queues-sample-in-rabbitmq/
https://www.rabbitmq.com/tutorials/tutorial-two-java.html

Work Queues Sample in RabbitMQ

July 16, 2017

Server : Consumer

public class Main {

    public static void main(String[] args) throws IOException, TimeoutException {
        String queueName = "queue2";

        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();

        Channel channel = connection.createChannel();

        channel.queueDeclare(queueName, true, false, false, null);
        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");

        channel.basicQos(1);

        Consumer consumer = new DefaultConsumer(channel) {
            @Override
            public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {
                String message=new String(body,"UTF-8");

                try {
                    doWork(message);
                }
                catch (Exception ex)
                {
                    ex.printStackTrace();
                }
                finally {
                    channel.basicAck(envelope.getDeliveryTag(),false);
                }
            }
        };

        channel.basicConsume(queueName,false,consumer);
    }

    public static void doWork(String message) throws InterruptedException {
        System.out.println(" [x] Received '" + message + "'");

        int sleepTime=new Random().nextInt(2000);

        Thread.sleep(sleepTime);
    }
}

Client : Producer

public class Main {

    public static void main(String[] args) throws IOException, TimeoutException, InterruptedException {

        String queueName = "queue2";

        ConnectionFactory factory = new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        channel.queueDeclare(queueName, true, false, false, null);

        int count = 0;

        while (count < 100) {

            Date date = new Date();

            String message = String.format("%d : %s", count, date.toString());

            channel.basicPublish("", queueName, MessageProperties.PERSISTENT_TEXT_PLAIN,
                    message.getBytes("UTF-8"));
            System.out.println(String.format(" [x] Sent %s", message));

            Thread.sleep(1000);
            count++;
        }
    }
}

References
https://www.rabbitmq.com/tutorials/tutorial-two-java.html
https://github.com/mhdr/RabbitMQSamples/tree/master/002_WorkQueues

Hello World Sample in RabbitMQ

July 16, 2017

Server

public class Main {

    public static void main(String[] args) throws IOException, TimeoutException {
        String queueName="Hello";

        ConnectionFactory factory=new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection = factory.newConnection();
        Channel channel = connection.createChannel();

        channel.queueDeclare(queueName,false,false,false,null);

        System.out.println(" [*] Waiting for messages. To exit press CTRL+C");


        Consumer consumer=new DefaultConsumer(channel){
            @Override
            public void handleDelivery(String consumerTag, Envelope envelope, AMQP.BasicProperties properties, byte[] body) throws IOException {

                String message=new String(body,"UTF-8");
                System.out.println(" [x] Received '" + message + "'");
            }
        };

        channel.basicConsume(queueName,true,consumer);
    }
}

Client

public class Main {
    public static void main(String[] args) throws IOException, TimeoutException, InterruptedException {

        String queueName="Hello";

        ConnectionFactory factory=new ConnectionFactory();
        factory.setHost("localhost");

        Connection connection= factory.newConnection();
        Channel channel= connection.createChannel();

        channel.queueDeclare(queueName,false,false,false,null);


        int count=0;

        while (count<100){
            Date date=new Date();
            String message=String.format("Hello World : %s", date.toString());

            channel.basicPublish("",queueName,null,message.getBytes("UTF-8"));

            System.out.println(" [x] Sent '" + message + "'");
            count++;

            Thread.sleep(1000);
        }

        channel.close();
        connection.close();
    }
}

References
https://www.rabbitmq.com/tutorials/tutorial-one-java.html
https://github.com/mhdr/RabbitMQSamples/tree/master/001_HelloWorld

Controlling System Limits on Linux for RabbitMQ

July 15, 2017

Ubuntu 16.04 :

create this file if it does not exist :

/etc/systemd/system/rabbitmq-server.service.d/limits.conf

and add this :

[Service]
LimitNOFILE=300000

sudo systemctl daemon-reload

sudo service rabbitmq-server restart

References
https://www.rabbitmq.com/install-debian.html
https://kimambo.de/increasing-limits-for-socket-descriptors-on-ubuntu-for-rabbitmq/

Working with greenDAO on Android

July 14, 2017

build.gradle

buildscript {
    repositories {
        jcenter()
        mavenCentral()
    }
    dependencies {
        classpath 'com.android.tools.build:gradle:2.3.3'
        classpath 'org.greenrobot:greendao-gradle-plugin:3.2.2'
    }
}

allprojects {
    repositories {
        jcenter()
    }
}

task clean(type: Delete) {
    delete rootProject.buildDir
}

build.gradle

apply plugin: 'com.android.application'
apply plugin: 'org.greenrobot.greendao'

android {
    compileSdkVersion 26
    buildToolsVersion "26.0.0"
    defaultConfig {
        applicationId "ir.mhdr.a097"
        minSdkVersion 17
        targetSdkVersion 26
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:26.+'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    compile 'org.greenrobot:greendao:3.2.2'

    // This is only needed if you want to use encrypted databases
    compile 'net.zetetic:android-database-sqlcipher:3.5.6'

    testCompile 'junit:junit:4.12'
}

App.java

public class App extends Application {

    public static final boolean ENCRYPTED = false;

    @Override
    public void onCreate() {
        super.onCreate();

        DaoMaster.DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, ENCRYPTED ? "notes-db-encrypted" : "notes-db");
        Database db = ENCRYPTED ? helper.getEncryptedWritableDb("super-secret") : helper.getWritableDb();
        Statics.daoSession = new DaoMaster(db).newSession();
    }
}

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="ir.mhdr.a097">

    <application
        android:name=".App"
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

Statice.java

public class Statics {

    public static DaoSession daoSession;
}

Note.java

@Entity(indexes = {
        @Index(value = "text, date DESC", unique = true)
})
public class Note {

    @Id(autoincrement = true)
    private Long id;

    @Index(unique = true)
    private String uuid;

    @NotNull
    private String text;

    @Property(nameInDb = "date")
    private Date date;

    @Transient
    private int tempUsageCount;

@Generated(hash = 102375063)
public Note(Long id, String uuid, @NotNull String text, Date date) {
    this.id = id;
    this.uuid = uuid;
    this.text = text;
    this.date = date;
}
@Generated(hash = 1272611929)
public Note() {
}
public Long getId() {
    return this.id;
}
public void setId(Long id) {
    this.id = id;
}
public String getText() {
    return this.text;
}
public void setText(String text) {
    this.text = text;
}
public Date getDate() {
    return this.date;
}
public void setDate(Date date) {
    this.date = date;
}
public String getUuid() {
    return this.uuid;
}
public void setUuid(String uuid) {
    this.uuid = uuid;
}
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private DaoSession daoSession;
    private NoteDao noteDao;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        daoSession = Statics.daoSession;
        noteDao = daoSession.getNoteDao();

        Note note = new Note();
        note.setUuid(UUID.randomUUID().toString());
        note.setDate(new Date());
        note.setText("Hello World");

        noteDao.save(note);
    }
}

if using Kotlin

android {
    ...
    sourceSets {
        main.java.srcDirs += 'build/generated/source/greendao'
    }
}

References
http://greenrobot.org/greendao/documentation/
https://github.com/mhdr/AndroidSamples/tree/master/097
https://github.com/greenrobot/greenDAO/issues/395

SSH Tunnel – Local and Remote Port Forwarding

July 13, 2017

Connecting to a database behind a firewall

ssh -L 9000:localhost:5432 user@example.com

Remote port forwarding

ssh -R 9000:localhost:3000 user@example.com

sudo nano /etc/ssh/sshd_config
GatewayPorts yes
sudo service ssh restart

References
http://blog.trackets.com/2014/05/17/ssh-tunnel-local-and-remote-port-forwarding-explained-with-examples.html