Classes on the fly ! Java

/**
 * Converge Systems
 * File Name : ConvergeJavaCompiler.java
 * Package Name : 
 * Purpose: Dynamic Compilation of java classes
 *
 * @author Abhinandan Panda		
 * @version 1.0 Oct 23, 2009	
 *
 */

import java.io.File;
import java.io.IOException;
import java.net.URISyntaxException;
import java.util.Arrays;
import java.util.Collections;
import java.util.Vector;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.StandardJavaFileManager;
import javax.tools.StandardLocation;
import javax.tools.ToolProvider;

public final class ConvergeJavaCompiler {

 // Generated cless files would reside here
public static final String CLASSPATH_LOCATION = "WebContent/WEB-INF/classes";
	public ConvergeJavaCompiler() {
	}
	private static boolean compile(JavaFileObject source[]) {
		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
		StandardJavaFileManager fileManager = compiler.getStandardFileManager(
				null, null, null);
		try {
			File file = new File(CLASSPATH_LOCATION);
			if (file.exists()) {
				fileManager.setLocation(StandardLocation.CLASS_OUTPUT,
						Collections.singleton(file));
			} else {
				file.mkdir();
				fileManager.setLocation(StandardLocation.CLASS_OUTPUT,
						Collections.singleton(file));
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
		javax.tools.JavaCompiler.CompilationTask task = compiler.getTask(null,
				fileManager, null, null, null, Arrays.asList(source));
		return task.call().booleanValue();
	}

	public boolean callDynamicCompiler(String className, String programText)
			throws URISyntaxException {
		boolean status = false;
		Vector vectorProgramText = (new ConvergeFileGenerator())
				.getJavaFilesInStringFormat(className, columnVector);
		int count = 0;
		for (String programText : vectorProgramText) {
			System.out.println("Compilation starting on :");
			System.out.println(programText);
			status = compile(new JavaFileObject[] { new RAMResidentJavaFileObject(
						className, programText)
			System.out.println("Compilation Status:"status);
		return status;
	}
}

                                                                                            

Using ActiveMQ

Active MQ primarily is used to do asynchronous batch processing. This can be used to send mails, poll data from database and process that in a batch. Message Queues have primarily 2 clients, a producer and one consumer. Producers are responsible to put messages to the MQ server while consumers continously listen to that port. A real world example of using MQ would be sending a mail to a user. Sending a mail requires a lot of time and is uncertain which if executed in the main thread would result in unwarranted user disruptions. So we need a producer which would just put the message in the MQ and let the MailConsumer poll data and do its work in the background.
A Simple producer :

/**
 * Converge Systems
 * File Name : ConvergeProducerTool.java
 * Package Name : 
 * Purpose: Dynamic Compilation of java classes
 *
 * @author Abhinandan Panda		
 * @version 1.0 Oct 23, 2009	
 *
 */
public class ConvergeProducerTool {

    private Destination destination;
    private long sleepTime;
    private long timeToLive;
    private String user = ActiveMQConnection.DEFAULT_USER;
    private String password = ActiveMQConnection.DEFAULT_PASSWORD;
    private String url = ActiveMQConnection.DEFAULT_BROKER_URL;
    private String subject = "convergesystems"; // MQ name. Create a MQ with this name in MQ server
    private boolean topic;
    private boolean transacted;
    private boolean persistent;


    public void run(String message) {
        Connection connection = null;
        try {
            if (timeToLive != 0) {
                System.out.println("Messages time to live " + timeToLive + " ms");
            }

            // Create the connection.
            ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(user, password, url);
            connection = connectionFactory.createConnection();
            connection.start();

            // Create the session
            Session session = connection.createSession(transacted, Session.AUTO_ACKNOWLEDGE);
            if (topic) {
                destination = session.createTopic(subject);
            } else {
                destination = session.createQueue(subject);
            }

            // Create the producer.
            MessageProducer producer = session.createProducer(destination);
            if (persistent) {
                producer.setDeliveryMode(DeliveryMode.PERSISTENT);
            } else {
                producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);
            }
            if (timeToLive != 0) {
                producer.setTimeToLive(timeToLive);
            }

            // Start sending messages
            sendLoop(message,session, producer);

            System.out.println("Done.");

            // Use the ActiveMQConnection interface to dump the connection
            // stats.
            ActiveMQConnection c = (ActiveMQConnection)connection;
            c.getConnectionStats().dump(new IndentPrinter());

        } catch (JMSException e) {
            System.out.println("JMSException::" + e);
           // e.printStackTrace();
        } catch (Exception e) {
            System.out.println("Caught: " + e);
            //e.printStackTrace();
        } finally {
            try {
                connection.close();
            } catch (Throwable ignore) {
            }
        }
    }

    protected void sendLoop(String emailId,Session session, MessageProducer producer) throws Exception {
            TextMessage message = session.createTextMessage(emailId);
            producer.send(message);
            if (transacted) {
                session.commit();
            }
            Thread.sleep(sleepTime);
    }


    public void setPersistent(boolean durable) {
        this.persistent = durable;
    }

    public void setMessageCount(int messageCount) {
    }

    public void setMessageSize(int messageSize) {
    }

    public void setPassword(String pwd) {
        this.password = pwd;
    }

    public void setSleepTime(long sleepTime) {
        this.sleepTime = sleepTime;
    }

    public void setSubject(String subject) {
        this.subject = subject;
    }

    public void setTimeToLive(long timeToLive) {
        this.timeToLive = timeToLive;
    }

    public void setTopic(boolean topic) {
        this.topic = topic;
    }

    public void setQueue(boolean queue) {
        this.topic = !queue;
    }

    public void setTransacted(boolean transacted) {
        this.transacted = transacted;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public void setUser(String user) {
        this.user = user;
    }

    public void setVerbose(boolean verbose) {
    }
}