jms-点对点

在点对点模式中，消息创建者称为发送者，消息消费者称为接收者。
特点
1.通过一个queque（队列）的通道传递。
2.队列可以被多个消费者申请监听，但是只有一个获取消息，获取后，消息会从队列去除。
3.消息是有顺序的（先进先出），但是设置优先级的除外。
4.消费者和发送者的无偶性，两者之间的先后运行顺序没有关系。

在监听模式（实现onMessage）是异步的，而调用receive方法则是同步，会占用本线程的资源。

General API	Point-to-point API
ConnectionFactory	QueueConnectionFactory
Destination	Queue
Connection	QueueConnection
Session	QueueSession
MessageConsumer	QueueSender
MessageProducer	QueueReceiver

以下例子（来源Java Message Service_2nd），是一个关于借贷的例子

package lyx.money;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

import javax.jms.JMSException;
import javax.jms.MapMessage;
import javax.jms.Queue;
import javax.jms.QueueConnection;
import javax.jms.QueueConnectionFactory;
import javax.jms.QueueReceiver;
import javax.jms.QueueSender;
import javax.jms.QueueSession;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;

public class QBorrower {
	private QueueConnection qConnect = null;
	private QueueSession qSession = null;
	private Queue responseQ = null;
	private Queue requestQ = null;

//这里也是初始化
	public QBorrower(String queuecf, String requestQueue, String responseQueue) {
		try {
			// Connect to the provider and get the JMS connection
			Context ctx = new InitialContext();
			QueueConnectionFactory qFactory = (QueueConnectionFactory) ctx
					.lookup(queuecf);
			qConnect = qFactory.createQueueConnection();
			// Create the JMS Session
			qSession = qConnect.createQueueSession(false,
					Session.AUTO_ACKNOWLEDGE);
			// Lookup the request and response queues
			requestQ = (Queue) ctx.lookup(requestQueue);
			responseQ = (Queue) ctx.lookup(responseQueue);
			// Now that setup is complete, start the Connection
//如果只是发送消息，而不需要接收消息，这部其实可以省略的，但是这种情况很少。
			qConnect.start();
		} catch (JMSException jmse) {
			jmse.printStackTrace();
			System.exit(1);
		} catch (NamingException jne) {
			jne.printStackTrace();
			System.exit(1);
		}
	}

	private void sendLoanRequest(double salary, double loanAmt) {
		try {
			// Create JMS message
			MapMessage msg = qSession.createMapMessage();
			msg.setDouble("Salary", salary);
			msg.setDouble("LoanAmount", loanAmt);
//这里有设置，当接收者要回复的时候，需要给哪个目标回复。这里使用的是另外一个通道，是因为接收者在接收的时候，没有进行过滤，会接收任何消息，使用另外一个通道是防止回复信息被其他接收者给接收掉。
			msg.setJMSReplyTo(responseQ);
			// Create the sender and send the message
//关于这里为何发送者和接收者都使用同一个session，而不是不同的session，其实可以这个例子的想象业务是发送一个贷款请求，系统需要等待有人处理申请，并等待处理结果，因此可以认为是同步的业务，这种情况使用同步会比异步更加合理。
			QueueSender qSender = qSession.createSender(requestQ);
			qSender.send(msg);
			// Wait to see if the loan request was accepted or declined
//这里有一个过滤器，这种过滤器是为了在获取贷款处理结果的时候，只获取自己的结果而不是别人的。
			String filter = "JMSCorrelationID = '" + msg.getJMSMessageID()
					+ "'";
			QueueReceiver qReceiver = qSession
					.createReceiver(responseQ, filter);
			TextMessage tmsg = (TextMessage) qReceiver.receive(3000000);
			if (tmsg == null) {
				System.out.println("QLender not responding");
			} else {
				System.out.println("Loan request was " + tmsg.getText());
			}
		} catch (JMSException jmse) {
			jmse.printStackTrace();
			System.exit(1);
		}
	}

	private void exit() {
		try {
			qConnect.close();
		} catch (JMSException jmse) {
			jmse.printStackTrace();
		}
		System.exit(0);
	}

//初始化的问题，不许多加说明
	public static void main(String argv[]) {
		String queuecf = null;
		String requestq = null;
		String responseq = null;
		if (argv.length == 3) {
			queuecf = argv[0];
			requestq = argv[1];
			responseq = argv[2];
		} else {
			System.out.println("Invalid arguments. Should be: ");
			System.out
					.println("java QBorrower factory requestQueue responseQueue");
			System.exit(0);
		}
		QBorrower borrower = new QBorrower(queuecf, requestq, responseq);
		try {
			// Read all standard input and send it as a message
			BufferedReader stdin = new BufferedReader(new InputStreamReader(
					System.in));
			System.out.println("QBorrower Application Started");
			System.out.println("Press enter to quit application");
			System.out.println("Enter: Salary, Loan_Amount");
			System.out.println("\ne.g. 50000, 120000");
			while (true) {
				System.out.print("> ");
				String loanRequest = stdin.readLine();
				if (loanRequest == null || loanRequest.trim().length() <= 0) {
					borrower.exit();
				}
				// Parse the deal description
				StringTokenizer st = new StringTokenizer(loanRequest, ",");
				double salary = Double.valueOf(st.nextToken().trim())
						.doubleValue();
				double loanAmt = Double.valueOf(st.nextToken().trim())
						.doubleValue();
				borrower.sendLoanRequest(salary, loanAmt);
			}
		} catch (IOException ioe) {
			ioe.printStackTrace();
		}
	}
}

jndi.properties

java.naming.factory.initial=org.apache.activemq.jndi.ActiveMQInitialContextFactory
java.naming.provider.url=tcp://localhost:61616
java.naming.security.principal=system
java.naming.security.credentials=manager
connectionFactoryNames=lyxcf
topic.topic1=jms.topic1
queue.qs=jms.qs
queue.qr=jms.qr

通过connection的ConnectionMetaData metadata = qConnect.getMetaData();放方法，可以获取到数据源，里面包含了一些信息。

System.out.println("JMS Version: " +
metadata.getJMSMajorVersion() + "." +
metadata.getJMSMinorVersion());
System.out.println("JMS Provider: " +
metadata.getJMSProviderName());
System.out.println("JMSX Properties Supported: ");
Enumeration e = metadata.getJMSXPropertyNames();
while (e.hasMoreElements()) {
System.out.println(" " + e.nextElement());
}

另外message必须通过session创建，以便完成对应的初始化，而不是通过new创建，new创建出来的对象，确实很多信息。

package lyx.money;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

import javax.jms.JMSException;
import javax.jms.MapMessage;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.Queue;
import javax.jms.QueueConnection;
import javax.jms.QueueConnectionFactory;
import javax.jms.QueueReceiver;
import javax.jms.QueueSender;
import javax.jms.QueueSession;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;

public class QLender implements MessageListener {
	private QueueConnection qConnect = null;
	private QueueSession qSession = null;
	private Queue requestQ = null;

	public QLender(String queuecf, String requestQueue) {
		try {
			// Connect to the provider and get the JMS connection
			Context ctx = new InitialContext();
			QueueConnectionFactory qFactory = (QueueConnectionFactory) ctx
					.lookup(queuecf);
			qConnect = qFactory.createQueueConnection();
			// Create the JMS Session
			qSession = qConnect.createQueueSession(false,
					Session.AUTO_ACKNOWLEDGE);
			// Lookup the request queue
			requestQ = (Queue) ctx.lookup(requestQueue);
			// Now that setup is complete, start the Connection
			qConnect.start();
			// Create the message listener
			QueueReceiver qReceiver = qSession.createReceiver(requestQ);
			qReceiver.setMessageListener(this);
			System.out.println("Waiting for loan requests...");
		} catch (JMSException jmse) {
			jmse.printStackTrace();
			System.exit(1);
		} catch (NamingException jne) {
			jne.printStackTrace();
			System.exit(1);
		}
	}

//使用监听模式
	public void onMessage(Message message) {
	try {
	boolean accepted = false;
	// Get the data from the message
	MapMessage msg = (MapMessage)message;
	double salary = msg.getDouble("Salary");
	double loanAmt = msg.getDouble("LoanAmount");
	// Determine whether to accept or decline the loan
	if (loanAmt < 200000) {
	accepted = (salary / loanAmt) > .25;
	} else {
	accepted = (salary / loanAmt) > .33;
	}
	System.out.println("" +
	"Percent = " + (salary / loanAmt) + ", loan is "
	+ (accepted ? "Accepted!" : "Declined"));
	// Send the results back to the borrower
	TextMessage tmsg = qSession.createTextMessage();
	tmsg.setText(accepted ? "Accepted!" : "Declined");
//为了和消息发送者保持逻辑一致，（这里有一定耦合度了）
	tmsg.setJMSCorrelationID(message.getJMSMessageID());
	// Create the sender and send the message
//在进行回复的时候，使用发送者指定的通道。
	QueueSender qSender =
	qSession.createSender((Queue)message.getJMSReplyTo());
	qSender.send(tmsg);
	System.out.println("\nWaiting for loan requests...");
	} catch (JMSException jmse) {
	jmse.printStackTrace();
	System.exit(1);
	} catch (Exception jmse) {
	jmse.printStackTrace();
	System.exit(1);
	}
	}

	private void exit() {
		try {
			qConnect.close();
		} catch (JMSException jmse) {
			jmse.printStackTrace();
		}
		System.exit(0);
	}

	public static void main(String argv[]) {
		String queuecf = null;
		String requestq = null;
		if (argv.length == 2) {
			queuecf = argv[0];
			requestq = argv[1];
		} else {
			System.out.println("Invalid arguments. Should be: ");
			System.out.println("java QLender factory request_queue");
			System.exit(0);
		}
		QLender lender = new QLender(queuecf, requestq);
		try {
			// Run until enter is pressed
			BufferedReader stdin = new BufferedReader(new InputStreamReader(
					System.in));
			System.out.println("QLender application started");
			System.out.println("Press enter to quit application");
			stdin.readLine();
			lender.exit();
		} catch (IOException ioe) {
			ioe.printStackTrace();
		}
	}
}

QueueBrowser
通过它可以访问队列中的快照

QueueSession session = connection.createQueueSession
(false, Session.AUTO_ACKNOWLEDGE);
QueueBrowser browser = session.createBrowser(queue);
Enumeration e = browser.getEnumeration();
while (e.hasMoreElements()) {
TextMessage msg = (TextMessage)e.nextElement();
System.out.println("Browsing: " + msg.getText());
}
browser.close();

动态队列
假设一种情况，有1000个发送者，都要使用不同的队列，并且队列存活期很短，那么可能想到是每个队列命名XXX1-XXXN这种方式，其实还有更好的方式
QueueSession.createTemporaryQueue()
这样创建的队列是临时的，并且只是针对一个connection而存在的。