BEA WebLogic Interview Questions and Answers 15

Which of the following are true about the transaction support in the WebLogic server?
a. WebLogic Server allows transactions to be terminated only by the client that created the transaction.
b. WebLogic Server does not support multithreaded transactional clients.
c. A client or a server object cannot invoke methods on an object that is participating in another transaction.
d. WebLogic server supports Nested Transactions

Choices A and C are correct. WebLogic Server provides a Transaction Service that supports transactions in EJB and RMI applications. WebLogic Server allows transactions to be terminated only by the client that created the transaction. WebLogic Server implements the flat transaction model. Nested transactions are not supported.
WebLogic Server supports multithreaded transactional clients. Clients can make transaction requests concurrently in multiple threads. In WebLogic Server, a client or a server object cannot invoke methods on an object that is infected with (or participating in) another transaction. The method invocation issued by the client or the server will return an exception. Also in WebLogic Server, clients using third-party implementations of the Java Transaction API (for Java applications) are not supported.

Which of the following programs can be created using the ZAC Publish Wizard tool?Choices:
a. Installer
b. Deployer
c. Bootstrap
d. Packager

Choices A and C are correct. To publish to a WebLogic Server, we can use the ZAC publish wizard. For this, the server must be running, and you will need to know a user and password that has permission to publish. You can also use the ZAC Publish Wizard to create a set of native programs - an installer and a bootstrap - for various operating systems that become part of a published Java application.
The installer program is a native executable that installs your published Java program on the local machine. It doesn't require a Java environment itself, so it can run out-of-the-box in the native OS. The bootstrap is also a native program; the user runs the bootstrap to invoke the published application. The bootstrap takes care of monitoring for updates, downloading and updating the user's application, and other administrative ZAC functions.

How do I configure WebLogic to use a SOCKS proxy?
You can configure a java.net socket to use SOCKS by setting a Java system property.

How does WebLogic support CORBA and client communication via IIOP?
"CORBA" support means many things to many people. It often means simply IIOP /ORB support and not much on CORBA services. WebLogic supports CORBA in multiple ways.
First, Java clients can tunnel through a CORBA environment to WebLogic Server. We call this "IIOP tunneling," and it is intended for use with applets coming through an IIOP firewall, such as the IONA Wonderwall product. This is a Java-to-Java model riding over an IIOP communications framework.
WebLogic RMI over IIOP provides RMI services for many clients (including CORBA clients) over IIOP.
WebLogic Enterprise Connectivity enables you to create IIOP connection pools to a BEA WebLogic Enterprise System, allowing you to execute WebLogic Enterprise CORBA objects from WebLogic Server servlets and Enterprise JavaBeans.

Can WebLogic Server start with a UNIX boot?
You can add a startup script to your UNIX rc scripts to run WebLogic Server at UNIX boot time. Here is an example from an HP-UX 11 system, running under JDK 1.1. You need to supply the URL for your WebLogic Server and your system password. This file, wlstart, is placed in the /sbin/init.d directory and there is a link to it in the /sbin/rc2.d directory:

export SHLIB_PATH=\
/home/user1/weblogic/lib/hpux11:/oracle/8.0.4/lib
export CLASSPATH=/home/user1/weblogic/classes:\
/home/user1/weblogic/lib/weblogicaux.jar
export ORACLE_home=/oracle/8.0.4
export ORACLE_SID=DEMO
export ORACLE_TERM=vt100
export QAT=/home/user1/weblogic
cd $QAT
PATH=/sbin:/usr/sbin:/usr/bin:/opt/java/bin
export PATH
case $1 in
'start')
java -ms64m -mx64m -verbosegc weblogic.Server > \
/home/user1/weblogic/server.out 2> #emp;
;;
'stop')
java weblogic.Admin URL shutdown system password
;;
*)
echo "usage: $0 {start|stop}"
;;
esac

You should work with your UNIX system administrator to set up scripts similar to this for your system

Why do I get "NoClassDefFound"/"Too Many Open files"messages on Solaris?
Problem: When I am using WebLogic Server on Solaris and try to run my application, I get a "NoClassDefFound" error, although the class causing the error does exist and is in the right directory. In fact, there are other classes in the same directory that are getting loaded. I also get a "Too many open files" error.

We have seen this situation when the user account runs out of file descriptors. On Solaris, each user account has a certain limited number of file descriptors. You can find out how many file descriptors you have with the limit command in csh.
You can increase file descriptors if you have enough privileges with the ulimit command in the csh. Otherwise, ask your system administrator to increase the file descriptors available to your processes.

A stateful session bean implementing the SessionSynchronization interface is deployed on the WebLogic server. Which of the following callback methods may be invoked on the bean?
a. beforeBegin
b. afterBegin
c. beforeCompletion
d. afterCompletion

Choices B, C and D are correct. A stateful session bean using container-managed transactions can implement the javax.ejb.SessionSynchronization interface to provide transaction synchronization notifications. This interface defines only 3 methods - afterBegin(), beforeCompletion() and afterCompletion().
The afterBegin() callback method is called when the bean becomes part of a transaction. It is called before the EJB Object delegates the business method invocation to the bean instance. If the transaction is committed, the bean will be notified through its beforeCompletion() method. If the transaction is rolled back, this method is not invoked. The afterCompletion() method is always invoked whether the transaction ended with a commit or a rollback. A is incorrect because beforeBegin is not a method defined in the SessionSynchronization interface.

The home of a Product CMP entity bean has a finder method, which returns an Enumeration of all the products whose price falls below a certain value, which is passed as the method argument. If there are no products in the database to match the above criteria what will be the result of a call to this finder method?
a. EJBException is thrown
b. ObjectNotFoundException is thrown
c. NoSuchEntityException is thrown
d. An empty enumeration is returned

Choice D is correct. Find methods that return a single remote reference throw a FinderException if an application error occurs and a ObjectNotFoundException if a matching bean cannot be found. The ObjectNotFoundException is a subtype of FinderException and is only thrown by find methods, which return single remote references.
The findByPrimaryKey() method returns only one remote reference since there is a one-to-one relationship between a primary key's value and an entity. Find methods that return an Enumeration or Collection type return an empty collection or enumeration if no matching beans can be found or throw a FinderException if an application error occurs. NoSuchEntityException is a system exception thrown by the ejbLoad() method of an entity bean when the database row to be loaded is not found and also by the ejbStore() method when the database row to be updated cannot be found. It is a subclass of EJBException.