Archive

Posts Tagged ‘JMS’

Difference in the overloaded createConnection() methods in javax.jms.ConnectionFactory

August 5th, 2007 Arun Manivannan No comments

This is the first thing you do when you work with JMS — Get a connection.

ConnectionFactory factory = (ConnectionFactory)ic.lookup("MyConnectionFactory");

conn = factory.createConnection(); // You call either this
conn = factory.createConnection(userName, password); // or this.

But, what is this “username” and “password” in your connection, when you have already
logged into your application server and there are no provisions to use them in the configured ConnectionFactory either.

Every server has a default (active) security realm.
A security realm is a container that includes users, groups, security roles,
security policies, and security providers, that are used to protect WebLogic resources.

A realm can have one or more users and these users can belong to one or more groups.

WebLogic Server has the following groups:

* Administrators
* Deployers
* Operators
* Monitors
* App Testers

Your login information for the admin server console is managed in this default security realm.
The user who logs in to the server console is the default administrator. He belongs to the group
“Administrators”.

I have a scenario, wherein a wholesaler and retailer are going to make use of the JMS Server for interchanging
their messages on their sales deals.

Neither the wholesaler nor the retailer is the owner of the JMS Server.
They are just guests who make use of this USERNAME and PASSWORD, passed in the
factory.createConnection(userName, password) to create a connection to their destination(Topic/Queue).

This is a way in which clients are authorized to access their relevant destinations.
In other words, only those clients who are authorized can have access to the destinations.

Here is how you configure users and groups in the security realm of Weblogic 9.2

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Categories: username Tags: , ,

An attempt was made to create a named consumer (name) on a connection with no clientID

July 31st, 2007 Arun Manivannan No comments

While creating a DurableSubscriber please do specify the client id before specifying a named consumer. Please have a look at the small code i wrote. Do remember to set the ClientID before creating a session from it. The clientID becomes null and immutable after the session is created. Also remember to give the same client id while creating a DurableSubscriber.

ClientID

Categories: Uncategorized Tags: ,

Merrill Lynch interview questions

July 13th, 2007 Arun Manivannan 1 comment

I am not sure how my previous post got deleted.  Let me tell you something before you go through the questions.  I had three tests and three tech rounds (actually speaking).  Most of the questions were just questions from my answers.  So, basically you drive the interview. Trust me, the interviewers are damn good in what they are doing.  Frankly, I never have faced anything like this before.  They asked a lot many questions but these are all i could recollect.  If not for Merrill Lynch, these questions will surely be helpful for you for some other company.

1) Table level and row level lock

2) How to force a row level lock in a select query (for update clause)

3) Explicit locking in oracle (NO)

4) Deadlock

5) Shared and Exclusive Lock

6) Difference between wait and sleep (the timout seconds as arguments)

7) static synchronized methods possible? YES
8) What do they mean? What does static synchronized methods lock? (locks java.lang.Class)

9) Is it possible for two threads to get into a same class if one of the methods is static synchronized and the other just synchronized?

10) Configure webservices (Axis) in weblogic

11) What is a multipool

12) Difference between Topic and Queue. How to identify packet loss in a Topic publishing?

13) XSLT, XSR? ( I have never heard of XSR)

14) DTD and XSD difference.

15) Why is there just one datatype called CDATA in DTD?

16) Difference between Complex and Simple datatype in XSD

17) How to validate an XML?

18) How to disable XML Validation in runtime when the XSD specified in the processing instruction (residing in a different machine) is not available

19) DOM and SAX difference.

20) Apache POI API (just because I had this on my resume)

21) >>> An Abstract class is an interface?

>>> An interface is an abstract class?

22) What is Rowid? Can we update the column?

23) What is TRANSACTION_SERIALIZABLE?

24) How to make an IO operation thread safe (use wait/notify model or use Java NIO)

25) Rules of Serialization

26) How to set security manager in a remote machine

27) What is a sandbox?

28) How to copy serialized contents from one object to another? (Use reflection??)

29) What is a JMS Exception?

30) How to create transaction ? (User Transaction or use EJBs)

31) Methods in javax.jta.UserTransaction

32) How to rollback a transaction in an EJB ? context.setRollbackOnly()

33) When does EJB automatically rollback transactions (When a SystemException is thrown)

34) What is twophase commit?

35) In a distributed transaction what is the requirement from the JDBC Driver Class (should be XA)

36) Is XA possible in all databases?

37) Are you contributing to Apache?

38) What projects in Apache have you used?

39) Business Delegate resides on the server-side? (One machine holding the web-tier and the another machine holding EJB-tier. Where will you place the BD?)

40) Role of a Service locator apart from lookups ? (Cache Home objects)

41) In a stateless session bean, there is no difference among Remote Objects. Why cant we cache the Remote Objects too? (????!!!)

42) Pattern of Home Objects in EJB (Proxy)

43) Difference between TIBCO and MQ based messaging model ? (Who knows)

44) What is stack overflow ? (Too many methods in a stack. Often comes in a uncontrolled recursive function)

45) How to increase the stack memory (I don’t know)

46) Increase the heap memory (Xmx and Xms)

47) Can we have a nested transaction? (Not in J2ee)

48) How to have a count of EJB users for a stateless session bean at any time (Remember ejbCreate gets called only once. After creation of the bean, the bean goes to the pool. EjbCreate doesn’t get called the second time)

49) How to link MDBs with Queue?

50) What is the need to have a QueueManager?

51) What gets returned ? (20)

public int m1(){

try{

return 10;

}

catch (Exception e){

}

finally{

return 20;

}

}

52) Why use Ajax?

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