The QueueBrowser object is simple to use. We will examine this listing from QWBrowser.examineQueue( ) in detail:

private int examineQueue(int inStockQty)
{
    int cnt = 0;
    int bestQty = 0;
    try  {
        System.out.println("In Stock QTY: " + inStockQty);
        System.out.print ( "Creating QueueBrowser..." );
        javax.jms.QueueBrowser browser 
            = qSession.createBrowser(receiveQueue);
        System.out.println ("[done]");

        java.util.Enumeration e = browser.getEnumeration( );
        while(e.hasMoreElements( )){
            System.out.print(" --> getting message " 
            	+ String.valueOf(++cnt) + "...");
            javax.jms.TextMessage message = 
                (javax.jms.TextMessage) e.nextElement( );
            System.out.println("[" + message.getText( ) + "]");
            if (message != null){
                int orderQty = message.getIntProperty("QTY");
                if ( orderQty > bestQty && orderQty <= inStockQty)
                    bestQty = orderQty;
            }
        }
        // Free any resources in the browser
        browser.close( );
    } catch ( javax.jms.JMSException jmse ){
        jmse.printStackTrace( );
    }
    System.out.println("
BestQty: " + bestQty);
    return bestQty;
}

First, note the call to create the QueueBrowser:

System.out.print ( "Creating QueueBrowser..." );
        javax.jms.QueueBrowser browser
            = qSession.createBrowser(receiveQueue);
        System.out.println ("[done]");

The method createQueueBrowser( ) is a session method. It takes a Queue object as a parameter and returns a QueueBrowser object. The createQueueBrowser( ) method, in additon, allows you to set a message selector using an overloaded method signature.

The QueueBrowser object contains a java.util.Enumeration that holds the messages in the queue. Here's how to use it:

...
java.util.Enumeration e = browser.getEnumeration( );
while(e.hasMoreElements( )){
    javax.jms.TextMessage message = 
        (javax.jms.TextMessage) e.nextElement( );
    System.out.println("[" + message.getText( ) + "]");
...

When the browser has served its purpose, it must be closed. This informs the JMS provider that it is no longer needed, thus allowing the provider to clean up any resources it may have allocated on the browser's behalf:

// Free any resources in the browser
        browser.close( );

Now let's look at the main input loop, which publishes the prices quotes, browses the queue, then uses a synchronous QueueReceiver to consume the messages after it has browsed them:

public void processInput( ){
    try  {
	   ...
        System.out.println ("Enter: Item, Old Price, New Price");
        System.out.println("
e.g. Bowling Shoes, 100.00, 55.00");
        String dealDesc = stdin.readLine( );
	    ...
        publishPriceQuotes(dealDesc,uname,
                    itemDesc, oldPrice,newPrice);

        int inStockQty = 
               (int)(java.lang.Math.random( ) * (double)1000);
        int bestQty = examineQueue(inStockQty);
        qConnect.start( ); // Start the connection
        javax.jms.TextMessage textMessage = null;
        while( true ){
            textMessage = 
                (javax.jms.TextMessage)qReceiver.receive(1000);
            if ( textMessage == null ){
                qConnect.stop( );
                break;  // No more messages to get
            }
            String text = textMessage.getText( );
            int qty = textMessage.getIntProperty("QTY");
            System.out.println("
Order received - "+text+
                " from " + textMessage.getJMSCorrelationID( ));

            if (qty == bestQty){
                System.out.println("Fulfilling order");
                // Do some processing to fulfill order
            } else {
                System.out.println("Placing in BACK-ORDER status");
                // Do some processing to create BACK-ORDER status
            }
        }
	...
}

Messages obtained from a QueueBrowser are copies of messages contained in the queue and are not considered to be consumed—they are merely for browsing.

It is important to note that the QueueBrowser is not guaranteed to have a definitive list of messages in the queue. The JMS specification allows the QueueBrowser to contain a snapshot, or a copy of, the queue as it appears at the time the QueueBrowser is created. The behavior may vary depending on vendor implementation, since the contents of the queue may change between the time the browser is created and the time you examine its contents. No matter how small that window of time is, new messages may arrive and other messages may be consumed by other JMS clients. Some JMS providers will update QueueBrowsers as the status of the queue changes while others will not.