Oracle Weblogic Interview Questions

By | May 23, 2013 | 2 Comment

1. What is a domain in weblogic server?

An Oracle WebLogic Server administration domain is a logically related group of Oracle WebLogic Server resources. Domains include a special Oracle WebLogic Server instance called the Administration Server, which is the central point from which you configure and manage all resources in the domain. Usually, you configure a domain to include additional Oracle WebLogic Server instances called Managed Servers.

2. What is an administration server?

The Administration Server operates as a central point of control for the configuration of the entire domain. It maintains the domain’s configuration documents and helps sync changes in the configuration documents to Managed Servers. You can also use the Administration Server as a central location that helps monitor all resources in a domain.

3. What is a managed server?

Managed Servers host business applications, application components, Web services, and their associated resources. Managed Servers maintain its own read-only copy of the domain’s configuration document. When a Managed Server starts up, it connects to the domain’s Administration Server to synchronize its version of the configuration document with the document that the Administration Server maintains.

4. What will happen if an administration server fails?

The failure of the administration server does not have any impact on the managed server. However, the domain configuration cannot be changed in the failed state as the admin server controls the domain configuration.

5. What are deployment descriptors?

Deployment descriptors are XML files that describe the runtime behaviour for the deployment unit or the application. These XML file contains information such as the context root of the web application, the parameters to be set on application start up and the mapping of the portable names of an application’s resources to the application Server’s resources. These descriptors lie in the WEB-INF or the META-INFdirectories.

6. What is MSI mode?

MSI mode, if enabled, helps in starting the managed server without starting the Admin server. With this option enabled, managed server looks for the msi-config.xml and creates an Mbean out of it.

7. What all possible ways can be used to stat the webogic server?

a). Using the startWeblogic.sh script.

b). Using Node Manager

c). Using weblogic.admin start command

d). As a windows service usingbeasvc.exe

8. What is the difference between web.xml and weblogic.xml?

The web.xml file provides configuration and deployment information for the Web components that comprise a Web application. Examples of Web components are servlet parameters, servlet and JavaServer Pages (JSP) definitions, and Uniform Resource Locators (URL) mappings. This is located in the WEB-INF directory.

Weblogic.xml is the configuration file for all the applications lying in the domain created. It lies in the META-INF directory and contains parameters such as auth-filter,  charset-params, container-descriptor,  context-root,  description etc.

9. What do you know about weblogic classloading?

A classloader is part of JVM that loads classes into memory. Classloader is responsible for finding the classes at runtime.

Weblogic uses the following classloaders:

  • Bootstrap classloader (JVM): Loads internal classes for JVM
  • Extensions classloader (JVM): Loads JARs placed in the extensions directory
  • Application classloader (WebLogic): Loads the EAR/WAR/EJB

10. What is a connection pool?

Connection pool is a named collection of identical JDBC connections to a database. This is done for the purpose of efficiency so as to reduce the overhead of creating connection objects at runtime.

11. What is JNDI?

JNDI or the Java Naming and Directory Interface is a naming service used to locate objects in datasources, JMS, MailSessions etc. It is a kind of abstraction that the clients use while connecting to the database. So the client looks for the JNDI to get the connection to the database.

12. What is JMS?

JMS or the Java Messaging Service helps the application sin a domain to communicate with one another. It simplifies the application development in weblogic by providing a set of methods through its API that help in creating, sending and receiving messages accross enterprise applications.

13. What is the difference between a JNDI and a datasource?

JNDI or the Java Naming and Directory Interface is a naming service used to locate objects in datasources, JMS, MailSessions etc. Datasource is an object used to access the connections in the pool. JNDI physically connects to the database whereas the datasource is a logical resource.

14. What is a weblogic server cluster?

Weblogic server cluster is a set of multiple weblogic servers running in parallel with each other to provide increased scalability, reliability and high availability. A cluster gives the end-user the feel of a single weblogic instance while multiple weblogic servers may be running simultaneously in the background. All cluster related information/parameters are defined in the weblogic.xml.

15. Is that possible to start Managed server if admin server is not running ?

Yes, if MSI is enabled.

16. What are the differene modes of Weblogic server?

In development mode, there is an application poller. This is a simple utility that polls the “<domain>/applications” directory every 3secs (default). If it finds a different version of application in the directory, then weblogic would redeploy the app automatically.

In production mode application poller is turned off. User would either have to deploy from console or run  weblogic.Deployer utility.

17. What is a virtual host?

A configured host name that routes requests for a particular DNS name to a WebLogic Server instance or cluster.

18. What are the different staging modes?

Stage: The Administration Server first copies the deployment unit source files to the staging directories of target servers. (The staging directory is named stage by default, and it resides under the target server’s root directory.)

The target servers then deploy using their local copy of the deployment files.

NoStage: The Administration Server does not copy deployment unit files. Instead, all servers deploy using the same physical copy of the deployment files, which must be directly accessible by the Administration Server and target servers.

External_Stage: External_stage mode is similar to stage mode, in that target servers deploy using local copies of the deployment files. However, the Administration Server does not automatically copy the deployment files to targeted servers in external_stage mode; instead, you must copy the files to the staging directory of each target server before deployment. You can perform the copy manually or use automated scripts.

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