WebLogic Application Server Interview Questions And Answers - DoAnswers.com

BEA Systems' WebLogic is a server software application that runs on a middle tier, between back-end databases and related applications and browser-based thin clients. WebLogic is a leading e-commerce online transaction processing (OLTP) platform, developed to connect users in a distributed computing environment and to facilitate the integration of mainframe applications with distributed corporate data and applications.

WebLogic server is based on Java 2 Platform, Enterprise Edition (J2EE), the standard platform used to create Java-based multi-tier enterprise applications. J2EE platform technologies were developed through the efforts of BEA Systems and other vendors in collaboration with the main developer, Sun Microsystems. Because J2EE applications are standardized modules, WebLogic can automate many system-level tasks that would otherwise have demanded programming time.

The main features of WebLogic server include connectors that make it possible for any legacy application on any client to interoperate with server applications, Enterprise JavaBean (EJB) components, resource pooling, and connection sharing that make applications very scalable. An administration console with a user interface makes management tasks more efficient and features such as Secure Sockets Layer (SSL) support for the encryption of data transmissions, as well as authentication and authorization mechanisms, make applications and transactions secure.

WebLogic Server installs the following script that you can use to set the classpath that a server requires:
WL_HOME\server\bin\setWLSEnv.cmd (on Windows)
WL_HOME/server/bin/setWLSEnv.sh (on UNIX)

where WL_HOME is the directory in which you installed WebLogic Server.

WebLogic Server uses two mechanisms to determine if a given server instance is unavailable.
Each WebLogic Server instance in a cluster uses multicast to broadcast regular "heartbeat" messages that advertise its availability. By monitoring heartbeat messages, server instances in a cluster determine when a server instance has failed. The other server instances will drop a server instance from the cluster, if they do not receive three consecutive heartbeats from that server instance
WebLogic Server also monitors socket errors to determine the availability of a server instance. For example, if server instance A has an open socket to server instance B, and the socket unexpectedly closes, server A assumes that server B is offline.

There are many possible configurations and each has its own advantages and disadvantages. BEA WebLogic Server has no built-in limit for the number of server instances that can reside in a cluster. Large, multi-processor servers such as Sun Microsystems, Inc. Sun Enterprise 10000, therefore, can host very large clusters or multiple clusters.
In most cases, WebLogic Server clusters scale best when deployed with one WebLogic Server instance for every two CPUs. However, as with all capacity planning, you should test the actual deployment with your target web applications to determine the optimal number and distribution of server instances.

Yes, we bundle an XSLT processor, based on Apache's Xalan 2.0.1 processor, in WebLogic Server 6.1.

Yes. In WebLogic Server 6.0 and later, EJBs must be homogeneously deployed across a cluster for the following reasons:

To keep clustering EJBs simple
To improve performance by avoiding cross-server calls. If EJBs are not deployed on all servers, cross-server calls are more likely.
To ensure that every EJB is available locall.y
To ensure that all classes are loaded in an undeployable way. Every server must have access to each EJB's classes so that it can be bound into the local JNDI tree. If only a subset of the servers deploys the bean, the other servers will have to load the bean's classes in their respective system classpaths which makes it impossible to undeploy the beans.

You may see messages like these in the log file: (Windows NT) java.io.IOException Connection Reset by Peer java.io.EOFException Connection Reset by Peer (Solaris) java.io.Exception: Broken pipe These messages occur when you are using servlets. A client initiates an HTTP request, and then performs a series of actions on the browser: 1. Click Stop or enter equivalent command or keystrokes 2. Click Refresh or enter equivalent command or keystrokes 3. Send a new HTTP request. The messages indicate that WebLogic Server has detected and recovered from an interrupted HTTP request.

17. What happens when a failure occurs and the stub cannot connect to a WebLogic Server instance?

When the failure occurs, the stub removes the failed server instance from its list. If there are no servers left in its list, the stubb uses DNS again to find a running server and obtain a current list of running instances. Also, the stub periodically refreshes its list of available server instances in the cluster; this allows the stub to take advantage of new servers as they are added to the cluster.

1. The data in session should consist only of Serialized objects. 2. Only setAttribute function should be used to set objects in session

19. What is the deployment order for the deployed server components in WebLogic server?

� JDBC Connection Pools � JDBC Multi Pools � JDCB Data Sources � JDBC Tx Data Sources � JMS Connection Factories � JMS Servers � Connector Components � EJB Components � Web App Components --- An examination of the log file .,.,

20. What is the difference between the WL_HOME/config/examples/applications folder and the WL_HOME/config/examples/stage folder?

The applications folder is intended for applications that are not yet ready for a production environment. WebLogic Server dynamically deploys the contents of the applications folder. The stage folder (or a folder that you create for the same purpose) is for storing copies of deployment files that are ready for deployment in a production environment (deployments that use the stage or external_stage deployment modes).