JBoss Interview Questions

With the development of technology, it is essential for business organizations to utilize open-source platforms, which help build and deploy the services to be the best fit for the business. Hence, the organizations are more focused on platforms like JBoss to help them build the applications efficiently within the given time deadlines. Most of the organizations are now utilizing JBoss for its unique features and integration.

1. What do you understand by the term JBoss and Jbpm?

Ans: JBoss: JBoss refers to an open-source application server. It is purely based on JEE technology.JBoss provides its extensive support to the cross-platform java applications. JBoss is designed and developed such that it is embedded with Apache Tomcat Web Server. It is flexible to work around any Java Virtual Machine. JBoss provides its extensive support to JNDI, Servlet/JSP, EJB, Clustering, Web Services, and IIOP Integration. 

2.What's the difference between Standalone mode and Domain mode?

Ans: Standalone mode: Standalone mode in JBoss is referred to as a single Java Virtual Machine process in which every JBoss server maintains its configuration. If you would like to use only one JVM or development environment, then the standalone mode is the best model to work on.

Domain mode: Domain mode includes multiple servers in the configuration management, is done in a centralized way, and is most commonly used in the production environment.

3. Do you think it is possible to put a JBoss server instance into multiple clusters at the same time?

Ans: Yes, it is technically possible to put a JBoss server instance into multiple clusters simultaneously. This process is generally not recommended or suggested as it increases the complexity level of management.

4. Which component handles cluster communication in JBoss?

Ans: JBoss includes a JGroups Framework framework that provides its service to enable the peer-peer communications between the different nodes available in a cluster. This framework is built on the top of a stack of a network communication protocol. It provides services like transportation, discovery, reliability, failure detection, cluster management services, etc.

5. What do you understand about JBoss cache in short?

Ans: JBoss Cache is referred to as a product that helps in caching the frequently accessed java objects. JBoss Cache helps in improving the performance of business applications. JBoss provides its extensive support in improving the applications' scalability by minimizing the unnecessary database access and decreasing the network traffic. JBoss has come up with fully transactional features and a highly configurable set of actions that help deal with the concurrent data access efficiently for the applications.

6.Multiple Domains in the same cluster and Multiple clusters in the same domain: which one of these configurations is possible

Ans: Let us gain an understanding of both the terms.

Multiple domains in the same cluster: The multiple domains in the same cluster can be obtained by starting two domains in the same network sharing the same multicast address and port. This is technically possible and occurs very rarely.

Multiple domains in the same domain: The multiple clusters in the same domain can be obtained by defining a different multicast address on each Server Group or even at Server Level. This way, your Servers will communicate through different multicast addresses, even if in the same domain, so they will make up separate clusters.

7. What do you think will happen if the Domain controller fails to work?

Ans: Domain Controller failure leads to problems in Domain configuration. If there is a failure in Domain Controller, it is not possible to perform the domain configuration management. One more plus is that though the domain controller fails, the single nodes' applications are preserved. It is also possible to choose a backup domain controller server using the below snippet code.


<domain-controller>

   <remote host="127.0.0.1" port="9999" security-realm="ManagementRealm" username="eap7admin">

      <discovery-options>

         <static-discovery name="backup" protocol="remote" host="127.0.0.1" port="19999"/>

      </discovery-options>

   </remote>

</domain-controller>

8. What is the process to perform the monitoring and detection of the bottleneck of an application?

Ans: There are different components that need to be measured in an application. The primary step is to find out where exactly the degradation is, whether it is internal or external, where exactly the application is spending all the time.The usage of the JBoss JMX agents and monitoring of the components deployed to the application server represents the first step. Jbprobe, a specialized tool, is used for examining the single object or the objects loaded in the memory. This is possible after finding the time spent by most of the components or libraries or most of the resources.

9.What do you understand by the term JTA? What is the process of starting a JTA transaction from a Servlet deployed on JBoss?

Ans: JTA stands for Java Transaction API. The JTA is mainly used to specify the standard Java interfaces between the Transaction Manager and the other parties involved in the distribution management system. JTA allows the applications to perform the distributed transactions, which usually refers to the transactions that access and update the data on two or more networked computer resources. JTA API has come up with three elements: a high-level transaction manager interface specifically for an application server, a high-level application transaction demarcation interface, standard Java mapping of the X/Open XA protocol intended for a transactional resource manager. A JTA transaction starts by allowing JBoss to register in the JNDI tree, a JTA User Transaction object, which manages a distributed transaction.

10. Briefly list out the differences between validate-on-match and background-validation? Can you use both of them?

Ans: The Validate-on-match option is used for the validation of the database connection every time. If the validate-on-match option is set to true, it is validated and checked out from the connection pool by utilizing the validation mechanisms specified in the next step.

The background-validation option fires a background validation as dictated by the background-validation-millis. It is not possible to apply both of them. They are found to be mutually exclusive.

11. What are the different logging services that are offered by the JBoss server?

Ans: The logging server helps the user log into the server and save its logging details, which are likely to be used again. The package that is used for logging is log4j. The logging onto a server is controlled from a central file that resides in the configuration file that is managed separately. The file name is given as log4j.xml, and this file defines a set of appending files that are also considered log files. The file follows a specific format that should go with the message, and it also includes a filtering option that is used to filter out the details that are not required. The output of this file gets to both the console, and a log file that is also called a server log is given in the log directory. Logging services are crucial as it helps in the management and keeps the defined data on the server of people who are logging in.

12.How is it possible to increase Java Heap Memory in JBoss 7?

Ans: It is possible to increase Java heap memory in a separate conf file. To improve memory for standalone;

  • Navigate to the bin folder
  • Edit the standalone.conf file and look for "JAVA_OPTS=" argument line
  • The default configuration will have a minimum of 64 MB and a maximum of 512 MB. You can increase to the desired value.

13.How To Install Jboss On Linux Server?

Ans: Installation of JBoss is effortless and straightforward. All you need to do is download the desired version from the JBoss official download page in zipping or gz format.

Once the desired version is downloaded, extract the file to the location you want to install. If you downloaded the zip format, then you can use the unzip command to remove it.

14. What protocol by default uses mod_cluster?

Ans: By default, the mod_cluster subsystem's balancer makes use of the multicast UDP to advertise its availability to the background workers.

15. What Is A .war, .ear Or A .jar File?

Ans: WAR – WAR refers to a web application archive. WAR is a jar file used to distribute a collection of JavaServer Pages, Java Servlets, Java classes, xml files, tag libraries, static web pages (Html & others), and other resources that constitute a web application.

JAR – JAR refers to Java Archive. JAR is an archive file format typically used to aggregate many Java class files and associated metadata and resources into one file to distribute application software, libs on the Java platform.

EAR – EAR refers to Enterprise Archive. EAR is used for packaging one or more models into a single archive so that the deployment of the various modules into the app server happens simultaneously and coherently.

16. Which JDK is needed to run Seam?

Ans: Seam only works on JDK 5.0 and above. It uses annotations and other JDK 5.0 features. The Seam runs beautifully on different application servers - just like everything else the Hibernate team does, this is not a JBoss-only thing.

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17. What's the default port to access the Administration Console in JBoss 7?

Ans: 9990 is the default port. If it's installed on server1, then you need to access like:

http://server1:9990/admin-console

18. What do you understand by the tern JBPM?

Ans: JBPM: JBoss JBPM is referred to as a workflow or BPM engine. It is the aspect that enables the creation of the business processes, which helps in coordinating the people, services, applications, which is one of the primary functionality of the BPM engine. The most important feature is the combination of the workflow application development with the process design. The JBoss JBPM designer is flexible to facilitate a strong link between the business analyst and technical developer.

19. How to start JBoss in standalone mode?

Ans: Go to the bin folder where JBoss is installed and start with the following command.

./standalone.sh

20. Is it possible for you to create a cluster in standalone mode?

Ans: Yes, clustering is possible in standalone mode. However, an application must be deployed on each server/JVM in standalone mode.

21. What is the process of deploying an application?

Ans: There are three possible ways to deploy an application in the JBoss application server.

  • Admin Console – you can deploy the necessary application files through the administration console.
  • Auto-deploy – leverage file system deployment scanner to auto-deploy files from the deployments folder.
  • Automation – use automation tool/ant/scripting to deploy an application.

22. What are the essential types available for marker file deployment?

Ans: The following are the important types available for the marker file deployment.

  • .dodeploy – instruct to deploy
  • .deployed – indicate the file is deployed
  • .pending – deployment is still pending
  • .undeployed – confirmation that application is undeployed
  • .failed – deployment is failed for some reason
  • .skipdeploy – instruct JBoss to ignore the files for auto-deployment

23. What do you need to set-up a cluster with JBoss?

Ans: Starting JBoss with the configuration contains everything needed for clustering: It has all the libraries for clustering:

- JGroups.jar, JBoss-cache.jar - Clustered beans (cluster-service.xml) - HA-JNDI - HTTP session replications (tc5-cluster-service.xml) - Farming - HA-JMS

24.What optimization could I use if the EJB container is the only point of write access to the database?

Ans: You could activate the "Commit Option A" that is, the container caches entity bean state between transactions. This option assumes that the container has exclusive access to the persistent store. Therefore it doesn't need to synchronize the in-memory bean state from the persistent store at the beginning of each transaction.

25. What do you know about SEAM?

Ans: Built on the standards Java Server Faces and EJB 3.0, JBoss Seam unifies component and programming models and delivers a consistent and robust framework for the rapid creation of web applications with Java EE 5.0. Seam simplifies web application development and enables new functionality that was difficult to implement by hand before, such as stateful conversations, multi-window operation, and handling concurrent fine-grained AJAX requests. Seam also unifies and integrates popular open source technologies like Facelets, Hibernate, iText, and Lucene.

26. Do you know how you could add support for Web Service transactions?

Ans: JBoss supports Web Services transactions, including extended transaction models explicitly designed for loosely-coupled, long-running business processes. J2EE transactions can integrate seamlessly with Web Services transactions using our integrated, bi-directional transaction bridge. Interoperability with many other vendors is provided out-of-the-box, and JBoss is an active participant in these standards.

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27. Does Seam run on other application servers besides JBoss?

Ans: The Seam runs beautifully on other application servers - just like everything else the Hibernate team does, this is not a JBoss-only thing.

28. Can I use AJAX with Seam?

Ans: Yes, Seam provides excellent support for AJAX. First, Seam supports the ICEfaces and Ajax4JSF Ajax component libraries for JSF. If you prefer a more "old fashioned" approach, Seam provides a complete JavaScript remoting framework which lets you call Seam components and subscribe to JMS topics directly from the client. Please refer to the Seam remoting example application on using AJAX remoting to implement a chat room.

29.What if you need to span your transaction across multiple Servlet invocations?

Ans: You can't go with a Servlet. A JTA transaction must start and finish within a single invocation (of the service() method). It would help if you considered using a Stateful SB. In an SFSB with a JTA transaction, the association between the bean instance and the transaction is retained across multiple client calls.

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30.What is the difference between Hibernate and EJB 3? Do not you think EJB 3 is just a clone of Hibernate?

Ans: The perception of EJB3 as being a simple clone of Hibernate is primarily based on developer familiarity with Hibernate and similarity of naming, as well as a common purpose, and that Hibernate is morphing itself into an EJB3 implementation based on the work going into the specification, not the other way around.

EJBs are supposed to be components, in the sense that they're not just one class but a set of categories, descriptors, and usage and management contracts. All of this allows a container (JBoss, Weblogic, etc.) to provide services to those components and to be able to reuse and distribute this component. These services are, among others, transactions, concurrent access control, security, instance pooling, etc.

Hibernate is "just" an ORM (Object/Relational Mapping) tool. Quick and dirty, this means you can store an object tree belonging to a class hierarchy in a relational DB without writing a single SQL query. Quite cool, IMO. But no transaction control, no instance pooling, no concurrency control, and indeed no security.

Conclusion

As the organizations are looking for talented and experienced professionals, this article would help you crack the interview without any issues.JBoss is one of the platforms that enable business organizations to meet the business requirements within the given timeframes. An individual needs to get trained and certified in JBoss Server, which would provide them with a piece of in-depth knowledge about the platform and help you attain the best career in the current times.

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Vineeth
Vineeth
Big Data & Business Intelligence
I Am Vineeth and is a full Big Data & Business Intelligence contributor for hkr trainings. Before that I was worked for IBM Software Group building database and middleware Big Data products. And am well aware of all IT technologies. And Am very much happy to be a part of this session. Thanks for being given me the opportunity to introduce myself. Contact me with my email or twitter account.

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