Solved

Enumeration Interface - Iterate backwards, Getting the size, Start iterating at a certain point

Posted on 2011-09-19
14
483 Views
Last Modified: 2012-05-12
I have had this issue for a while now, and I'm hoping that someone can help me with this. I have a java class that connects to a queue using the jmx QueueBrowser api. I used its getEnumeration() method in order to iterate through the messages on a Weblogic queue as this is the only way that is provided. The messages are returned in the way a queue works (FIFO).

Questions:
--------------------
1. Is there a way to iterate through this Enumeration starting from the last message on published to the queue, essentially working with it as if it were a stack and not a queue?

2. Is there a way to get the total size of the Enumeration without first converting it to a Collection? Note: I tried the code below and it killed the performance of my application to the point where it was not usable (takes an extremely long time to do this conversion).

List<BrowserVO> messagesList = Collections.list(queueBrowser.getEnumeration());
int total = messagesList.size();

3. Is there a way to start iterating through an Enumeration at a certain spot (not at the first element)? I tried to convert it to a collection first, but performance is a major issue (see #2 above). I'd like to be able to return messages 1-50 to the caller, and then 51-100, and so on based on the caller's request. Right now, I can only return the first n items and that's it.

Thanks again.

private static final String JNDI_FACTORY = "weblogic.jndi.WLInitialContextFactory";
	private static final String JDBC_DRIVER_CLASS_NAME = "oracle.jdbc.driver.OracleDriver";
	private int numMsgs;
	private int totalMsgs;
	
	@SuppressWarnings({ "rawtypes", "unchecked" })
	public ArrayList browseJmsQueue(String server, String queueName,String connectionFactoryName,String user,String pass) throws Exception
	{
		
		ArrayList list = new ArrayList();
		numMsgs = 0;
		
	 	
	 	try
	 	{
	 		Hashtable env = new Hashtable();
	        env.put(Context.INITIAL_CONTEXT_FACTORY, JNDI_FACTORY);
	        env.put(Context.PROVIDER_URL, server);
	        InitialContext ctx1 = new InitialContext(env);
		 	Queue queue = (Queue) ctx1.lookup(queueName);
		 	QueueConnectionFactory connFactory = (QueueConnectionFactory) ctx1.lookup(connectionFactoryName);
		 	QueueConnection queueConn = connFactory.createQueueConnection(user,pass);
		 	QueueSession queueSession = queueConn.createQueueSession(false,Session.AUTO_ACKNOWLEDGE);
		 	QueueBrowser queueBrowser = queueSession.createBrowser(queue);
		 	queueConn.start();
		 	
			Enumeration<BrowserVO> e = queueBrowser.getEnumeration();
			
			//List<BrowserVO> messages = Collections.list(queueBrowser.getEnumeration());
			//ArrayList <BrowserVO>aList = Collections.list(e);
			//Iterator iterator = IteratorUtils.asIterator(e);
			//ListIterator listIterator = IteratorUtils.singletonListIterator(iterator);
			
			
			
			BrowserVO valueObj = null;
			while (e.hasMoreElements() && numMsgs<50) 
			{
				Message message = (Message) e.nextElement();
				numMsgs++;
				
				String messageStr = ((TextMessage)message).getText();
				
				try
				{
					valueObj = new BrowserVO();
					valueObj.setMessage(messageStr);
					
					list.add(valueObj);
				}
				catch(Exception e1)
				{
					//Ignore the messages that don't fit the type I am looking for
				}
			}
			
			System.out.println("Total Messages: "+numMsgs);
			
			queueConn.close();
        }
       
	 	catch(Exception e)
	 	{
	 		throw new QueueBrowserException(e.toString());
	 	}
	 	
		return list;
	}

Open in new window

0
Comment
Question by:jrwalker2
  • 8
  • 5
14 Comments
 
LVL 47

Expert Comment

by:for_yan
ID: 36562629
0
 
LVL 47

Expert Comment

by:for_yan
ID: 36562633
0
 
LVL 47

Expert Comment

by:for_yan
ID: 36562646
0
Master Your Team's Linux and Cloud Stack!

The average business loses $13.5M per year to ineffective training (per 1,000 employees). Keep ahead of the competition and combine in-person quality with online cost and flexibility by training with Linux Academy.

 
LVL 47

Expert Comment

by:for_yan
ID: 36562780


That's waht I read here:
http://www.theserverside.com/discussions/thread.tss?thread_id=1618

Enumerations don't have a size as they don't contain anything. You can get the size of the container, but an enumeration is essentially a const(in terms of the refrence not the object) iterator. Its responsibiliy is to know where the next item is. If you have a handle to the container being iterated I would suggest checking to see if it has a size method (most do).
0
 
LVL 47

Expert Comment

by:for_yan
ID: 36562822
But I guess you should be getting the collection in the first place
this looks like some backwards operation of creating collection from enumeartion again:
List<BrowserVO> messagesList = Collections.list(queueBrowser.getEnumeration());

There should be some collection before enumeration
0
 
LVL 47

Expert Comment

by:for_yan
ID: 36562963
maybe you can just try

queueBrowser.size()


maybe it inherits form Collection interface
0
 
LVL 47

Expert Comment

by:for_yan
ID: 36563514
Yes, I understand you tries all that with ListIterator
Looks like this is indeed a problem; they were probably not designed to be traversed in different way;
maybe there is still some solution

Maybe you want to consume messages not to browse through them ?
0
 
LVL 1

Author Comment

by:jrwalker2
ID: 36563637
Hi for_yan,

Thanks for your responses but you are right, this is still an issue. My requirement will not allow me to consume the messages (only browse them). Since I am using a WebLogic Server, I'm thinking that I might be able to access the JMS MBean to get this information. I'm still looking for some code.

Thanks
0
 
LVL 47

Accepted Solution

by:
for_yan earned 500 total points
ID: 36563659

Well, thiis code I ncuountered when I borwsed about it of course not for you and your requirements, but
maybe will lead you to some insights
http://stackoverflow.com/questions/2461870/how-to-purge-delete-message-from-weblogic-jms-queue
0
 
LVL 86

Expert Comment

by:CEHJ
ID: 36563853
>>(takes an extremely long time to do this conversion).

How much faster (if at all) is it to simply enumerate with the Enumeration?
0
 
LVL 1

Author Comment

by:jrwalker2
ID: 36564788
Thanks for_yan for your comments. I ended up solving the count issue with an MBean implementation. Please see the code below. I will award you the full points for your persistent attempts.

CEHJ - I'm not sure what you mean by "enumerate with the Enumeration". I was not asking how to enumerate over the Enumeration. If you take a look at the code I originally posted, you will see that I am doing exactly that (iterating through the first fifty messages and incrementing a counter along the way). The issue with this is that it requires me to iterate through all the messages...takes too long.



int totalCurrentMessageCount; 
		
		try
		{
			Hashtable env = new Hashtable();
			env.put(Context.PROVIDER_URL, server);
			env.put(Context.SECURITY_PRINCIPAL, user);
			env.put(Context.SECURITY_CREDENTIALS, pass);
			env.put(Context.INITIAL_CONTEXT_FACTORY,"weblogic.jndi.WLInitialContextFactory");
			InitialContext ctx = new InitialContext(env);

			Destination queue = (Destination) ctx.lookup(queueName);

			JMSDestinationRuntimeMBean destMBean = JMSRuntimeHelper.getJMSDestinationRuntimeMBean(ctx, queue);
			
			totalCurrentMessageCount = (int)destMBean.getMessagesCurrentCount();
			
			
		}
		catch(Exception e)
		{
			throw new QueueBrowserException(e.toString());
		}

Open in new window

0
 
LVL 1

Author Comment

by:jrwalker2
ID: 36564803
I've requested that this question be closed as follows:

Accepted answer: 500 points for for_yan's comment http:/Q_27316085.html#36563659
Assisted answer: 0 points for jrwalker2's comment http:/Q_27316085.html#36564788

for the following reason:

Accepting my comment because I ended up solving my own issue. The solution was different than anything suggested.
0
 
LVL 1

Author Comment

by:jrwalker2
ID: 36564795
Accepting my comment because I ended up solving my own issue. The solution was different than anything suggested.
0
 
LVL 1

Author Comment

by:jrwalker2
ID: 36564804
intend to assign points to for_yan
0

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Apps blocked by Java 9 88
How do I remove an object from a 3 40
add projects t working set in maven 2 23
servlet and mdb, jms error 1 33
Introduction Java can be integrated with native programs using an interface called JNI(Java Native Interface). Native programs are programs which can directly run on the processor. JNI is simply a naming and calling convention so that the JVM (Java…
In this post we will learn how to connect and configure Android Device (Smartphone etc.) with Android Studio. After that we will run a simple Hello World Program.
Viewers learn about the “while” loop and how to utilize it correctly in Java. Additionally, viewers begin exploring how to include conditional statements within a while loop and avoid an endless loop. Define While Loop: Basic Example: Explanatio…
Viewers learn about the scanner class in this video and are introduced to receiving user input for their programs. Additionally, objects, conditional statements, and loops are used to help reinforce the concepts. Introduce Scanner class: Importing…

837 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question