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Java EE - Interview Questions and Answers for 'J2ee' - 46 question(s) found - Order By Newest

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Q1. Explain Flow of Spring MVC ?

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Ans. The DispatcherServlet configured in web.xml file receives the request.

The DispatcherServlet finds the appropriate Controller with the help of HandlerMapping and then invokes associated Controller.

Then the Controller executes the logic business logic and then returns ModeAndView object to the DispatcherServlet.

The DispatcherServlet determines the view from the ModelAndView object.

Then the DispatcherServlet passes the model object to the View.

The View is rendered and the Dispatcher Servlet sends the output to the Servlet container.

Finally Servlet Container sends the result back to the user.

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Q2. What is session tracking and how do you track a user session in servlets?

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Ans. Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:

User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password

Hidden form fields - fields are added to an HTML form that are not displayed in the client's browser. When the form containing the fields is submitted, the fields are sent back to the server

URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.

Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser.

HttpSession- places a limit on the number of sessions that can exist in memory.

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Very frequently asked.Usually among first few questions.

Q3. What is MVC ?

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Ans. MVC is a Design Pattern that facilititates loose coupling by segregating responsibilities in a Web application

1. Controller receives the requests and handles overall control of the request
2. Model holds majority of the Business logic, and
3. View comprise of the view objects and GUI component

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Very frequently asked in companies using SOA.

Q4. What are RESTful Web Services ?

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Ans. REST or Representational State Transfer is a flexible architecture style for creating web services that recommends the following guidelines -

1. http for client server communication,
2. XML / JSON as formatiing language ,
3. Simple URI as address for the services and,
4. stateless communication.

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Q5. What is an API ( Application Programming Interface ) ?

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Ans. An API is a kind of technical contract which defines functionality that two parties must provide: a service provider (often called an implementation) and an application. an API simply defines services that a service provider (i.e., the implementation) makes available to applications.

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Q6. What is URL?

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Ans. URL is Uniform Resource Locator which is representation of HTTP address.

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Q7. What is HTTP ?

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Ans. HTTP or Hypertext Transfer Protocol is internet protocol for tranmission of hypertext ( text with meta data ) over internet.

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Q8. Is tomcat an application or Web server ?

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Ans. Tomcat is a web server and a Servlet container. It is often used as an application server for web-based applications but does not include the complete suite of capabilities that a Java EE application server would supply.

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Q9. Is Apache an application or Web server ?

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Ans. Web server.

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Q10. What is meant by an "asynchronous event." Give some examples ?

Operating System

^Anonymous

Ans. An asynchronous event is one that occurs at an unpredictable time outside the control of the program that the CPU is running. It is not "synchronized" with the program.

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Q11. Can we have multiple servlets in a web application and How can we do that ?

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Ans. Yes by making entries in web.xml

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Q12. How can we manage Error Messages in the web application ?

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Ans. Within message.properties file.

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Q13. Why Struts 1 Classes are not Thread Safe whereas Struts 2 classes are thread safe ?

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Ans. Struts 1 actions are singleton. So all threads operates on the single action object and hence makes it thread unsafe.

Struts 2 actions are not singleton and a new action object copy is created each time a new action request is made and hence its thread safe.

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Q14. What are the components of J2EE ?

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Ans. applets
Client component like Client side Java codes.
Web component like JSP, Servlet WAR
Enterprise JavaBeans like Session beans, Entity beans, Message driven beans
Enterprise application like WAR, JAR, EAR

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Q15. What bean scopes does Spring support? Explain them.

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Ans. The Spring Framework supports following five scopes -

Singleton
prototype
request
session
global-session

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Q16. Difference between socket and servlet ?

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Ans. servlet is a small, server-resident program that typically runs automatically in response to user input.
A network socket is an endpoint of an inter-process communication flow across a computer network.

We can think of it as a difference between door and gate. They are similar as they both are entry points but they are different as they are put up at different areas.

Sockets are for low-level network communication whereas Servlets are for implementing websites and web services

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Q17. What are different types of cookies ?

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Ans. Session cookies , which are deleted once the session is over.

Permanent cookies , which stays at client PC even if the session is disconnected.

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Q18. What is a cookie ?

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Ans. A cookie is a small piece of text stored on a user's computer by the browser for a specific domain. Commonly used for authentication, storing site preferences, and server session identification.

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Q19. Explain JMS ( Java Messaging Services ) ?

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Ans. JMS Provides high-performance asynchronous messaging. It enables Java EE applications to communicate with non-Java systems on top of various transports.

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Q20. Explain EJB (Enterprise Java Beans) ?

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Ans. EJB Provides a mechanism that make easy for Java developers to use advanced features in their components, such as remote method invocation (RMI), object/ relational mapping (that is, saving Java objects to a relational database), and distributed transactions across multiple data sources.

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Q21. Which MVC is struts2 based on ?

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Ans. MVC2

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Q22. Explain features of struts2 ?

^Anonymous

Ans. 1) It is an Action based MVC based framework which has adopt mvc2.

2) Struts2 is a pull-MVC (or MVC2) framework where action takes the role of the model rather than the controller. The â€œpullâ€ concepts means views ability to pull data from an action, rather than having a separate model object available.

3) The Model View-Controller pattern in Struts2 is implemented with five core components â€“ actions, interceptors, value stack / OGNL, result types and results / view technologies.

4) XML configuration as well as Annotation option available.

5) POJO based action available so we can write test cases easily.

6) Integration with Spring, tiles and OGNL based expression langugae.

7) Theme based tag libraries integrated with struts tag as well as support of Ajax tag.

8) Can have various view options like jsp, velocity, freemarker etc.

9) We can embed plugin through which we can modify and extend framework features.

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Q23. what is content negotiation?

^Anonymous

Ans. Suppose we want to visit a site for any information, information can be represented in different languages like English,German or may be other and their format for presentation can also differ from HTML to PDF or may be Plain text. In this case when an client makes an HTTP request to a server, client can also specify the media types here. Client can specify what it can accept back from host and on the basis of availability the host will return to the client. This is called content negotiation because client and server negotiated on the language and format of the content to be shared.

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Q24. What is a config Object?

^Anonymous

Ans. The config object is an instantiation of javax.servlet.ServletConfig and is a direct wrapper around the ServletConfig object for the generated servlet. This object allows the JSP programmer access to the Servlet or JSP engine initialization parameters such as the paths or file location.

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Q25. What is a pageContext Object?

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Ans. The pageContext object is an instance of a javax.servlet.jsp.PageContext object. The pageContext object is used to represent the entire JSP page. This object stores references to the request and response objects for each request. The application, config, session, and out objects are derived by accessing attributes of this object.The pageContext object also contains information about the directives issued to the JSP page, including the buffering information, the errorPageURL, and page scope.

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Q26. What is J2EE? What are J2EE components and services?

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Ans. J2EE or Java 2 Enterprise Edition is an environment for developing and deploying enterprise applications. The J2EE platform consists of J2EE components, services, Application Programming Interfaces (APIs) and protocols that provide the functionality for developing multi-tiered and distributed Web based applications.

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Q27. What are LDAP servers used for ?

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Ans. LDAP servers are typically used in J2EE applications to authenticate and authorise users. LDAP servers are hierarchical and are optimized for read access, so likely to be faster than database in providing read access.

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Q28. What are different modules of spring ?

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Ans. There are seven core modules in spring

Spring MVC
The Core container
O/R mapping
DAO
Application context
Aspect Oriented Programming or AOP
Web module

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Q29. What is Spring configuration file?

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Ans. Spring configuration file is an XML file. This file contains the classes information and describes how these classes are configured and introduced to each other.

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Q30. Q: What is default scope of bean in Spring framework?

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Ans. The default scope of bean is Sing leton for Spring framework.

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Very Frequently asked Spring question.

Q31. What is bean auto wiring?

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Ans. The Spring container is able to autowire relationships between collaborating beans. This means that it is possible to automatically let Spring resolve collaborators (other beans) for your bean by inspecting the contents of the BeanFactory without using and elements.

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Q32. What are the phases of the JSP life cycle ?

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Ans. Translation of JSP PageCompilation of JSP PageClassloading (class file is loaded by the classloader)Instantiation (Object of the Generated Servlet is created).Initialization ( jspInit() method is invoked by the container).Reqeust processing ( _jspService() method is invoked by the container).Destroy ( jspDestroy() method is invoked by the container).

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Q33. Difference between the jsp scriptlet tag and jsp declaration tag?

^Anonymous

Ans. The jsp scriptlet tag can only declare variables not methods whereas jsp declaration tag can declare variables as well as methods.

The declaration of scriptlet tag is placed inside the _jspService() method whereas The declaration of jsp declaration tag is placed outside the _jspService() method.

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Q34. What are JSP directives ? What are different types of directives ?

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Ans. The jsp directives are messages that tells the web container how to translate a JSP page into the corresponding servlet.

There are three types of directives -

page directive
include directive
taglib directive

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Q35. Which markup languages can be used in restful web services ?

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Ans. XML and JSON ( Javascript Object Notation ).

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Q36. What are advantages of using Servlets over CGI ?

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Ans. Better Performance as Servlets doesn't require a separate process for a single request.

Servlets are platform independent as they are written in Java.

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Q37. What is the use of HTTPSession in relation to http protocol ?

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Ans. http protocol on its own is stateless. So it helps in identifying the relationship between multiple stateless request as they come from a single source.

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Q38. Why using cookie to store session info is a better idea than just using session info in the request ?

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Ans. Session info in the request can be intercepted and hence a vulnerability. Cookie can be read and write by respective domain only and make sure that right session information is being passed by the client.

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Q39. http protocol is by default ... ?

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Ans. stateless

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Q40. Difference between jar , war and ear ?

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Ans. Jar is Java Archieve i.e compressed Class or Class / Java files.

War comprises of compressed Servlet class files,JSP FIles,supporting files, GIF and HTML files.

Ear comprise of compressed Java and web module files ( was files ).

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