RabbitMQ Publisher Subscribe Example in Java on Ubuntu

To install RabbitMQ on Ubuntu is as simple as executing:

sudo apt-get install rabbitmq-server

Next we need to download the java client libraries as they are not included in the ubuntu package. You can find the libraries at http://www.rabbitmq.com/java-client.html Unzip the archive and include the jars in your classpath

First we need a way of creating connections to RabbitMQ and also a method to setup exchanges, queues and routing keys: import com.rabbitmq.client.*; import java.io.IOException; import java.util.logging.Level; import java.util.logging.Logger; public class RabbitMQFactory { private static int DEFAULT_PORT = 5672; // The default port RabbitMQ runs on public static final String EXCHANGE = "testExchange"; public static final String QUEUE = "testQueue"; public static final String ROUTINGKEY = "testRoutingKey"; public static Channel getDefaultChannel() throws IOException { ConnectionFactory factory = new ConnectionFactory(); factory.setPassword("guest"); factory.setPassword("guest"); factory.setVirtualHost("/"); factory.setHost("localhost"); factory.setPort(DEFAULT_PORT); return factory.newConnection().createChannel(); } public static void createQueue(String exchange, String queue, String key) { try { Channel channel = getDefaultChannel(); channel.exchangeDeclare(exchange, "direct", true); channel.queueDeclare(queue, true, false, false, null); channel.queueBind(queue, exchange, key); } catch (IOException ex) { Logger.getLogger(RabbitMQFactory.class.getName()).log(Level.SEVERE, null, ex); } } // Create the topics public static void main(String[] args) { createQueue(EXCHANGE, QUEUE, ROUTINGKEY); } } Run the main method to setup our test queue.

Then create the publisher: import com.rabbitmq.client.Channel; import com.rabbitmq.client.Connection; import java.io.IOException; import java.util.Date; import java.util.Random; public class Producer { public static void main(String[] args) throws IOException, InterruptedException { Random random = new Random(); Channel channel = RabbitMQFactory.getDefaultChannel(); while(true) { String msgText = "Current time is: " + new Date().toString(); System.out.println("Adding msg: " + msgText); channel.basicPublish(RabbitMQFactory.EXCHANGE, RabbitMQFactory.ROUTINGKEY, null, msgText.getBytes()); Thread.sleep(random.nextInt(5) * 1000); } } }

Then the consumer import com.rabbitmq.client.Channel; import com.rabbitmq.client.QueueingConsumer; import com.rabbitmq.client.QueueingConsumer.Delivery; import java.io.IOException; import java.util.Date; import java.util.Random; public class Consumer { public static void main(String[] args) throws IOException, InterruptedException { Random random = new Random(); Channel channel = RabbitMQFactory.getDefaultChannel(); QueueingConsumer cons = new QueueingConsumer(channel); channel.basicConsume(RabbitMQFactory.QUEUE, false, cons); while(true) { Delivery delivery = cons.nextDelivery(); System.out.println("Got Message: " + new String(delivery.getBody())); channel.basicAck(delivery.getEnvelope().getDeliveryTag(), false); } } }

The execute the main method on the Publisher and Consumer and watch the messages flow.

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Grails Accessing Raw XML from a Request

There have been times in a grails controller I've wanted direct access to the xml in a POST request. You can retreive this via the request object: request.reader.text But what if you need access the raw xml and then to also use the xmlslurper to pick apart the xml. Accessing the request.XML after request.reader.xml throws this exception: java.lang.IllegalStateException: getReader() has already been called for this request

Say I have the following xml:
<one> <two>test line</two> <three> ... </three> </one>

and I want to access the raw xml tag 'three' but I want programmatic access to the tag 'two'. The following allows that: def xml = request.reader.text def three = xml =~ /(?m)(<three.*<\/three>)/ # multine regex def parsed = new XmlParser().parseText(xml) def two = parsed.one.two.text()

Grails Script to Copy Jar Dependencies

The usual way to include jar dependencies in Grails is to set the versioned dependencies in the BuildConfig.groovy. One issue I can see with this is that it forces you to use Maven, Ivy or at the very least a directory structure that is versioned. While this is a good practice and should be encouraged, there are times when you have to work with legacy build systems and you dont have the benefit of good structure. A script such as the following can copy the jars into the lib directory of the grails project. Call it something like Copyjars.groovy and put it in the scripts directory in the root of the grails project.


includeTargets << grailsScript("Init") target(main: "Copy jar dependencies") { Ant.copy(toDir: "${basedir}/lib", overwrite: true) { fileset(file: "${basedir}/../../myproject/lib/*jar") switch (grailsEnv) { case "production": fileset(file: "${basedir}/../../myproject/PRD/config-PRD.jar") break default: fileset(file: "${basedir}/../../myproject/DEV/config-DEV.jar") break } } } setDefaultTarget(main)


Then run the script using "grails prod copyjars"

Grails Jar'd Configuration Property Files

Say you have an existing Java project which has a plethora of configuration property files and you want to use some of these properties in your new Grails project. How can you do this? One approach is to:

1. Put all your property files into a jar and place the jar in the 'lib' directory of your grails project
2. Modify the Config.groovy and add the line -

   grails.config.locations = [ "classpath:file1.properties", "classpath:file2.properties" ]

3. Then depending where you are in the app you have access to the property variables and can dereference them e.g. ${my.file1.prop}