J2EE interview questions
Thanks to Sachin Rastogi for contributing these.
1. What makes J2EE suitable for distributed multitiered Applications?
- The J2EE platform uses a multitiered distributed application model. Application
logic is divided into components according to function, and the various
application components that make up a J2EE application are installed on different
machines depending on the tier in the multitiered J2EE environment to which the
application component belongs. The J2EE application parts are:
o Client-tier components run on the client machine.
o Web-tier components run on the J2EE server.
o Business-tier components run on the J2EE server.
o Enterprise information system (EIS)-tier software runs on the EIS server.
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2. What is J2EE? - J2EE is an environment for developing and deploying enterprise
applications. The J2EE platform consists of a set of services, application
programming interfaces (APIs), and protocols that provide the functionality for
developing multitiered, web-based applications.
3. What are the components of J2EE application?
- A J2EE component is a self-contained functional software unit that is assembled
into a J2EE application with its related classes and files and communicates with
other components. The J2EE specification defines the following J2EE
components:
1. Application clients and applets are client components.
2. Java Servlet and JavaServer Pages technology components are web
components.
3. Enterprise JavaBeans components (enterprise beans) are business
components.
4. Resource adapter components provided by EIS and tool vendors.
4. What do Enterprise JavaBeans components contain? - Enterprise JavaBeans
components contains Business code, which is logic
that solves or meets the needs of a particular business domain such as banking,
retail, or finance, is handled by enterprise beans running in the business tier. All
the business code is contained inside an Enterprise Bean which receives data from
client programs, processes it (if necessary), and sends it to the enterprise
information system tier for storage. An enterprise bean also retrieves data from
storage, processes it (if necessary), and sends it back to the client program.
5. Is J2EE application only a web-based? - No, It depends on type of application
that client wants. A J2EE application can be web-based or non-web-based. if an
application client executes on the client machine, it is a non-web-based J2EE
application. The J2EE application can provide a way for users to handle tasks
such as J2EE system or application administration. It typically has a graphical
user interface created from Swing or AWT APIs, or a command-line interface.
When user request, it can open an HTTP connection to establish communication
with a servlet running in the web tier.
6. Are JavaBeans J2EE components? - No. JavaBeans components are not
considered J2EE components by the J2EE specification. They are written to
manage the data flow between an application client or applet and components
running on the J2EE server or between server components and a database.
JavaBeans components written for the J2EE platform have instance variables and
get and set methods for accessing the data in the instance variables. JavaBeans
components used in this way are typically simple in design and implementation,
but should conform to the naming and design conventions outlined in the
JavaBeans component architecture.
7. Is HTML page a web component? - No. Static HTML pages and applets are
bundled with web components during application assembly, but are not
considered web components by the J2EE specification. Even the server-side
utility classes are not considered web components, either.
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8. What can be considered as a web component? - J2EE Web components can be
either servlets or JSP pages. Servlets are Java programming language classes that
dynamically process requests and construct responses. JSP pages are text-based
documents that execute as servlets but allow a more natural approach to creating
static content.
9. What is the container? - Containers are the interface between a component and
the low-level platform specific functionality that supports the component. Before
a Web, enterprise bean, or application client component can be executed, it must
be assembled into a J2EE application and deployed into its container.
10. What are container services? - A container is a runtime support of a systemlevel
entity. Containers provide components with services such as lifecycle
management, security, deployment, and threading.
11. What is the web container? - Servlet and JSP containers are collectively referred
to as Web containers. It manages the execution of JSP page and servlet
components for J2EE applications. Web components and their container run on
the J2EE server.
12. What is Enterprise JavaBeans (EJB) container? - It manages the execution of
enterprise beans for J2EE applications.
Enterprise beans and their container run on the J2EE server.
13. What is Applet container? - IManages the execution of applets. Consists of a
Web browser and Java Plugin running on the client together.
14. How do we package J2EE components? - J2EE components are packaged
separately and bundled into a J2EE application for deployment. Each component,
its related files such as GIF and HTML files or server-side utility classes, and a
deployment descriptor are assembled into a module and added to the J2EE
application. A J2EE application is composed of one or more enterprise bean,Web,
or application client component modules. The final enterprise solution can use
one J2EE application or be made up of two or more J2EE applications, depending
on design requirements. A J2EE application and each of its modules has its own
deployment descriptor. A deployment descriptor is an XML document with an
.xml extension that describes a component’s deployment settings.
15. What is a thin client? - A thin client is a lightweight interface to the application
that does not have such operations like query databases, execute complex business
rules, or connect to legacy applications.
16. What are types of J2EE clients? - Following are the types of J2EE clients:
o Applets
o Application clients
o Java Web Start-enabled rich clients, powered by Java Web Start
technology.
o Wireless clients, based on Mobile Information Device Profile (MIDP)
technology.
17. What is deployment descriptor? - A deployment descriptor is an Extensible
Markup Language (XML) text-based file with an .xml extension that describes a
component’s deployment settings. A J2EE application and each of its modules has
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its own deployment descriptor. For example, an enterprise bean module deployment
descriptor declares transaction attributes and security authorizations
for an enterprise bean. Because deployment descriptor information is declarative, it
can be changed without modifying the bean source code. At run time, the J2EE server
reads the deployment descriptor and acts upon the component accordingly.
18. What is the EAR file? - An EAR file is a standard JAR file with an .ear
extension, named from Enterprise ARchive file. A J2EE application with all of its
modules is delivered in EAR file.
19. What is JTA and JTS? - JTA is the abbreviation for the Java Transaction API.
JTS is the abbreviation for the Jave Transaction Service. JTA provides a standard
interface and allows you to demarcate transactions in a manner that is independent
of the transaction manager implementation. The J2EE SDK implements the
transaction manager with JTS. But your code doesn’t call the JTS methods
directly. Instead, it invokes the JTA methods, which then call the lower-level JTS
routines. Therefore, JTA is a high level transaction interface that your application
uses to control transaction. and JTS is a low level transaction interface and ejb
uses behind the scenes (client code doesn’t directly interact with JTS. It is based
on object transaction service(OTS) which is part of CORBA.
20. What is JAXP? - JAXP stands for Java API for XML. XML is a language for
representing and describing text-based data which can be read and handled by any
program or tool that uses XML APIs. It provides standard services to determine
the type of an arbitrary piece of data, encapsulate access to it, discover the
operations available on it, and create the appropriate JavaBeans component to
perform those operations.
21. What is J2EE Connector? - The J2EE Connector API is used by J2EE tools
vendors and system integrators to create resource adapters that support access to
enterprise information systems that can be plugged into any J2EE product. Each
type of database or EIS has a different resource adapter. Note: A resource adapter
is a software component that allows J2EE application components to access and
interact with the underlying resource manager. Because a resource adapter is
specific to its resource manager, there is typically a different resource adapter for
each type of database or enterprise information system.
22. What is JAAP? - The Java Authentication and Authorization Service (JAAS)
provides a way for a J2EE application to authenticate and authorize a specific user
or group of users to run it. It is a standard Pluggable Authentication Module
(PAM) framework that extends the Java 2 platform security architecture to
support user-based authorization.
23. What is Java Naming and Directory Service? - The JNDI provides naming and
directory functionality. It provides applications with methods for performing
standard directory operations, such as associating attributes with objects and
searching for objects using their attributes. Using JNDI, a J2EE application can
store and retrieve any type of named Java object. Because JNDI is independent of
any specific implementations, applications can use JNDI to access multiple
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24. naming and directory services, including existing naming and
directory services such as LDAP, NDS, DNS, and NIS.
25. What is Struts? - A Web page development framework. Struts combines Java
Servlets, Java Server Pages, custom tags, and message resources into a unified
framework. It is a cooperative, synergistic platform, suitable for development
teams, independent developers, and everyone between.
26. How is the MVC design pattern used in Struts framework? - In the MVC
design pattern, application flow is mediated by a central Controller. The
Controller delegates requests to an appropriate handler. The handlers are tied to a
Model, and each handler acts as an adapter between the request and the Model.
The Model represents, or encapsulates, an application’s business logic or state.
Control is usually then forwarded back through the Controller to the appropriate
View. The forwarding can be determined by consulting a set of mappings, usually
loaded from a database or configuration file. This provides a loose coupling
between the View and Model, which can make an application significantly easier
to create and maintain. Controller: Servlet controller which supplied by Struts
itself; View: what you can see on the screen, a JSP page and presentation
components; Model: System state and a business logic JavaBeans.
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