Introduction
This document describes how messages can be sent to and received from a messaging queue and how those messages can be processed in a Java class to add an order to a JobScheduler job chain.
No JobScheduler libraries are needed for this example.
Mode Of Operation
- Creating a message producer to send messages to a Message Queue (MQ) server.
- Creating a message consumer to receive messages from a MQ server.
- Sending the message to a Jobscheduler.
To be able to process the message on the desired JobScheduler the message has to be a XML snippet wich can be processed by the JobScheduler API respectively by the JobScheduler XML interface.
The MessageProducer
This example describes how to build a connection to a MQ server and send a message to a queue on this server. This example uses Apache Active MQ as the message queue server.
Most of the implementation was done with the standard jms implementation of Java. The only class from the active MQ implementation is the ActiveMQConnectionFactory class.
- Create a connection.
- Create a session.
- Create a destination.
- Create a producer.
- Send a message with the producer.
- Close the connection.
The Methods
To make the implementation more readable as well as reusable, the steps are separated in different methods.
The createConnection(String url) method
This method instantiates a ConnectionFactory object with an ActiveMQConnectionFactory object and creates a Connection object through the factory method createConnection().
The ActiveMQConnectionFactory object has to be instantiated with the URL of the MQ server.
public Connection createConnection(String uri){
ConnectionFactory factory = new ActiveMQConnectionFactory(uri);
Connection connection = null;
try {
connection = factory.createConnection();
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to connect: " , e);
}
return connection;
}
The createSession(Connection connection) method
The method is called with an already instantiated Connection object and initiates a Session object through the Connection objects createSession(boolean transacted, int acknowledgeMode) method.
private Session createSession(Connection connection){
Session session = null;
try {
session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to create Session: " , e);
}
return session;
}
The createDestination(Session session, String queueName) method
This method creates a Destination object. It is called with an active Session object and the name of the queue to write to. The Destination object is initiated through the createQueue(String name) method of the Session object.
public Destination createDestination(Session session, String queueName){
Destination destination = null;
try {
destination = session.createQueue(queueName);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to create Destination: " , e);
}
return destination;
}
The createMessageProducer(Session session, Destination destination) method
This method is called with an already active Session object as well as instantiated Destination object. It instantiates a MessageProducer object with the given session and destination.
private MessageProducer createMessageProducer(Session session, Destination destination){
MessageProducer producer = null;
try {
producer = session.createProducer(destination);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to create MessageProducer: " , e);
}
return producer;
}
The write(String text, MessageProducer producer) method
The method is called with the message to send to the server and the MessageProducer object to use for publishing. The message is a String object. The method instantiates a Message object with the text to send.
public void write(String text, MessageProducer producer){
Message message = null;
try {
if(text != null){
message = session.createTextMessage(text);
} else{
message = session.createTextMessage(DEFAULT_TEXT);
}
producer.send(message);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to write Message to Destination: " , e);
}
}
The close() method
This methods makes sure that the used connection will be closed after a message is sent.
private void close(Connection connection){
if (connection != null) {
try {
connection.close();
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to close the connection: " , e);
}
}
}
The SOSProducer class
The code example below slightly differs from the examples above. In the class below the methode write(String text) already uses the other method for instantiation, therfore it needs less parameters and it closes the connection itself.
The text in the example below consists of a JobScheduler add_order XML, which can later be used to send to a JobScheduler.
package com.sos.jms.producer;
import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.Destination;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageProducer;
import javax.jms.Session;
import org.apache.activemq.ActiveMQConnectionFactory;
import org.apache.log4j.Logger;
public class SOSProducer {
private static final String DEFAULT_CONNECTION_URI = "tcp://[HOSTNAME]:61616";
private static final Logger LOGGER = Logger.getLogger(SOSProducer.class);
private static final String QUEUE_NAME = "test_queue";
private static final String DEFAULT_TEXT = "<add_order job_chain='[FOLDERNAME]/[JOBCHAINNAME]' at='now'>"
+ "<params>"
+ "<param name='host' value='[HOST]'/>"
+ "<param name='port' value='22'/>"
+ "<param name='user' value='[USERNAME]'/>"
+ "<param name='auth_method' value='password'/>"
+ "<param name='password' value='[PASSWORD]'/>"
+ "<param name='command' value='echo command send over MessageQueue!'/>"
+ "</params>"
+ "</add_order>";
private Connection createConnection(){
return this.createConnection(DEFAULT_CONNECTION_URI);
}
public Connection createConnection(String uri){
ConnectionFactory factory = new ActiveMQConnectionFactory(uri);
Connection connection = null;
try {
connection = factory.createConnection();
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to connect: " , e);
}
return connection;
}
private Session createSession(Connection connection){
Session session = null;
try {
session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to create Session: " , e);
}
return session;
}
private Destination createDestination(Session session, String queueName){
Destination destination = null;
try {
destination = session.createQueue(queueName);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to create Destination: " , e);
}
return destination;
}
private MessageProducer createMessageProducer(Session session, Destination destination){
MessageProducer producer = null;
try {
producer = session.createProducer(destination);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to create MessageProducer: " , e);
}
return producer;
}
public void write(String text){
Connection connection = createConnection();
Session session = createSession(connection);
Destination destination = createDestination(session);
MessageProducer producer = createMessageProducer(session, destination);
Message message = null;
try {
if(text != null){
message = session.createTextMessage(text);
} else{
message = session.createTextMessage(DEFAULT_TEXT);
}
producer.send(message);
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to write Message to Destination: " , e);
} finally {
if (connection != null) {
try {
connection.close();
} catch (JMSException e) {
LOGGER.error("JMSException occurred while trying to close the connection: " , e);
}
}
}
}
}
The MessageConsumer
This example describes how to build a connection to a MQ server and receive a message from a queue on this server. This example uses Apache Active MQ as the message queue server.
- Create a connection.
- Create a session.
- Create a destination.
- Create a consumer.
- Receive a message with the consumer.
- Close the (MQ) connection.
- Open a TCP connection to a JobScheduler instance.
- Send the Message to the JobScheduler
- Close the (TCP) connection.