Java Interview Questions -36

Java Interview Questions -36

1.What is ActionMapping in struts?
Action mapping defines the flow of one request. The possible sequence is
User -> request -> Form -> Validation -> Business Code -> Forward -> JSP -> response -> User.
The components involved are Action classes, Forms and JSP.

2.What are the advantages of having multiple struts-config in the same application?

The implementation with many struts-config is to organize the development work, so that many people may be involved and it is some organized way of doing things. But this would result in some compromise in performance(speed). Technically there is no any difference between single and multiple struts-config files.

3.What are the ways in which resource file can be used in struts?

Defining message resources in struts-config file.
Programmatically using resource files in Java classes or in JSP files.

4.Explain the term ‘architecture of the application’?

Architecture is the set of rules (or framework) to bring in some common way of assembling or using J2EE components in the application. This helps in bringing consistency between codes developed by various developers in the team.

5.Which is the architecture followed by struts?

Struts follows MVC architecture.

6.Differentiate between the terms ‘Design Patterns’, ‘Framework’ and ‘Architecture’.

Design Pattern: The various solutions arrived at for the known problem. This helps to avoid re-inventing the wheel. The risk-free solution can be easily used by others. For example, singleton is the design pattern that you can use instantly to enfore one object per class. You do not need to think of this on your own.
Framework: A framework is a structure or set of rules, used to solve or address complex issues. It is basically a reusable designf for the J2EE applications. For example, Struts, JSF,etc., are the frameworks. You can use these frameworks based on the requirements of your application and each has its own set of advantages.
Architecture: It is a design that describes how the various components in the application fit together. For example, MVC is an architecture which is helpful to define how the components interact within the application.

7.Are Struts’s action classes Thread-safe?

Yes. Action classes are based on “one-instance and many-threads”. This is to conserve resources and to provide the best possible throughput.

8.What are the various Struts Tag libraries?

There are various struts tags. But the most-repeated tags are:

9.What is the difference between ActionForm and DynaActionForm?

In action form, you need to define the form class that extends ActionForm explicitly, whereas you can define the form dynamically inside the struts-config file when using DynaActionForm.

10.How can you use Validator framework in struts?

Validator Frameworks are helpful when the application needs server-side validation such that the particular set of validations occur very frequently within the same application. This avoids writing complex code in validation() method in every form bean. Using validator framework, there are different pre-written validations in place. You can customize these validations in XML file.

11.What are client-side and server-side vaidations?

Client-side validations: These are the validations that id done using javascripts. There is always a danger involved that the user can get through (crack-through) these validations. But for some simple validations, like converting lower-case to upper-case or date validations can be done, you can use javascripts.
Server-side validations: These are the validations done in server-side using Java components (Form bean or in business logics) where the user has no chance to crookedly get through the system.

12.Define the terms authentication and authorisation.

Authentication is the process/rule that validates if the user is allowed to access the system or not.
Authorization is the process/rule that validates if the user is allowed to access the particular part of the system or not. This occurs after user’s successful authentication.

13.What are the components provided in J2EE to perform authentication and authorization?

Authentication – RequestProcessor and/or Filter.
Authorization – DTO, JDO or Java or Action classes.

14.Give the difference between between ‘DispatchAction’ and ‘Action’.

A DispatchAction contains various different methods other than the standard execute() method in Action classes. These methods are executed based on some request parameter. For example, you can code in such a way that three buttons (namely Insert, Delete, Update) buttons correspond to different methods such as insert(), delete() and udpate(). The submit button in JSP would have the property that has the value which matches to any one of the methods defined in DispatchAction class.

15.What is pagination technique? How can you design them in struts?

Pagination is the technique where the bulk of results are split into different pages and only the information where the user can conveniently see are displayed in a page. (Like in Goooooogle). This can be achieved in many ways, but the simplest method is to have a query string (say http://www.testwebsite?pageNumber=2) would lead to information corresponding to resultset rows from 11 to 20. Assuming that you want to display 10 related rows of information, you can set the formula as follows:
Starting row = (pageNumber-1) * + 1 which is equal to 11.
Ending row = Starting row + which is equal to 20.

16.How can you populate the drop-down list using form properties?

There are many ways for this. But the best method is to use which defines collection that needs to be used to populate the drop-down list, the property to store the selected value and the collection that is used to display the labels (what we see in JSP page). For Example,
html:options collection=”form-collection-property”

17.What is the XML parser provided in struts? Can you use it for other purposes?

‘Digester’ framework. Yes we can use for our applications to store and parse our application-related data.

18.What is an “Action Class”?

The “Action Class” is part of the “Model” and is a wrapper around the business logic.The purpose of the “Action Class” is to translate the HttpServletRequest to the business logic.To use the “Action”, we need to subclass and overwrite the execute() method.
All the database and business processing is done in the “Action” class.It is advisable to perform all the database related work in the “Action” class.The ActionServlet (command) passes the parameterized class to ActionForm using the execute() method.
The return type of the execute method is ActionForward which is used by the Struts Framework to forward the request to the file according to the value of the returned ActionForward object.

19.Write code of any Action Class?

Here is the code of Action Class that returns the ActionForward object.
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
public class TestAction extends Action{

public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request,
HttpServletResponse response) throws Exception{
return mapping.findForward(“testAction”);

20.What is an “ActionForm”?

An “ActionForm” is a JavaBean that extends org.apache.struts.action.ActionForm.
ActionForm maintains the session state for web application and the “ActionForm” object is automatically populated on the server side with data entered from a form on the client side.

21.What is Struts Validator Framework?

The “Struts Framework” provides the functionality to validate the form data.It can be used to validate the data in the user’s browser as well as on the server side.
Struts Framework checks the JavaScript code and it can be used to validate the form data on the client browser.Server side validation of form data can be accomplished by subclassing your “form” Bean with DynaValidatorForm class.
The “Validator” framework was developed by David Winterfeldt as a third-party “add-on” to Struts.Now the Validator framework is part of the “Jakarta Commons” project and it can be used with or without Struts.
The Validator framework comes integrated with the Struts Framework andcan be used without any making any additional settings.

22.Describe the details of XML files used in the “Validator Framework”?

The Validator Framework uses two XML configuration files
1) validator-rules.xml and
2) validation.xml.
The validator-rules.xml defines the standard validation routines.
These are reusable and used in validation.xml to define the form specific validations.The validation.xml defines the validations applied to a form bean.

23.How would you display “validation fail” errors on a JSP page?

Following tag displays all the errors:

24.How can one enable front-end validation based on the xml in validation.xml?

The<html:javascript>tag allows front-end validation based on the xml in validation.xml.

25.What is Bean Factory ?

A BeanFactory is like a factory class that contains a collection of beans. The BeanFactory holds Bean Definitions of multiple beans within itself and then instantiates the bean whenever asked for by clients.
BeanFactory is able to create associations between collaborating objects as they are instantiated. This removes the burden of configuration from bean itself and the beans client. BeanFactory also takes part in the life cycle of a bean, making calls to custom initialization and destruction methods.

26.What is Application Context?

A bean factory is fine to simple applications, but to take advantage of the full power of the Spring framework, you may want to move up to Springs more advanced container, the application context. On the surface, an application context is same as a bean factory.Both load bean definitions, wire beans together, and dispense beans upon request. But it also provides:
A means for resolving text messages, including support for internationalization.A generic way to load file resources.Events to beans that are registered as listeners.

27.What is the difference between Bean Factory and Application Context

On the surface, an application context is same as a bean factory. But application context offers much more..Application contexts provide a means for resolving text messages, including support for i18n of those messages.Application contexts provide a generic way to load file resources,
such as images.Application contexts can publish events to beans that are registered as listeners.Certain operations on the container or beans in the container, which have to be handled in a programmatic fashion with a bean factory, can be handled declaratively in an application context.
ResourceLoader support: Spring’s Resource interface us a flexible generic abstraction for handling low-levelresources. An application context itself is a ResourceLoader, Hence provides an application with access to deployment-specific Resource instances.
MessageSource support: The application context implements MessageSource, an interface used to obtain localized messages, with the actual implementation being pluggable

28.What do you mean by Bean wiring ?

The act of creating associations between application components (beans) within the Spring container is reffered to as Bean wiring.

29.What do you mean by Auto Wiring?

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. The autowiring functionality has five modes. · no · byName · byType · constructor · autodirect

30.What is DelegatingVariableResolver?

Spring provides a custom JavaServer Faces VariableResolver implementation that extends the standard Java Server Faces managed beans mechanism which lets you use JSF and Spring together. This variable resolver is called as DelegatingVariableResolver

31.How to integrate your Struts application with Spring?

To integrate your Struts application with Spring, we have two options:
Configure Spring to manage your Actions as beans, using the ContextLoaderPlugin, and set their dependencies in a Spring context file.
Subclass Spring’s ActionSupport classes and grab your Spring-managed beans explicitly using agetWebApplicationContext()

32.What are the ways to access Hibernate using Spring ?

There are two approaches to Spring’s Hibernate integration:
1.Inversion of Control with a HibernateTemplate and Callback
2.Extending HibernateDaoSupport and Applying an AOP Interceptor nodes.

33.What is AOP? and How the AOP used in Spring?

Aspect-oriented programming, or AOP, is a programming technique that allowsprogrammers to modularize crosscutting concerns, or behavior that cuts across the typical divisions of responsibility, such as logging and transaction management. The core construct of AOP is the aspect, which encapsulates behaviors affecting multiple classes into reusable modules.
AOP is used in the Spring Framework: To provide declarative enterprise services, especially as a replacement for EJB declarative services. The most important such service is declarative transaction management, which builds on the Spring Framework’s transaction abstraction.To allow users to implement custom aspects, complementing their use of OOP with AOP.

34.Explain about the Spring DAO support

The Data Access Object (DAO) support in Spring is aimed at making it easy to work with data access technologies like JDBC, Hibernate or JDO in a consistent way. This allows one to switch between the persistence technologies fairly easily and it also allows one to code without worrying about catching exceptions that are specific to each technology.

35.What is SQLExceptionTranslator ?

SQLExceptionTranslator, is an interface to be implemented by classes that can translate between SQLExceptions and Spring’s own data-access-strategy-agnostic org.springframework.dao.DataAccessException.

36.What is the Core container module?

This module is provides the fundamental functionality of the spring framework. In this module BeanFactory is the heart of any spring-based application. The entire framework was built on the top of this module. This module makes the Spring container.

37. What is Application context module?

The Application context module makes spring a framework. This module extends the concept of BeanFactory, providing support for internationalization (I18N) messages, application lifecycle events, and validation. This module also supplies many enterprise services such JNDI access, EJB integration, remoting, and scheduling. It also provides support to other framework.

38. What is AOP module?

The AOP module is used for developing aspects for our Spring-enabled application. Much of the support has been provided by the AOP Alliance in order to ensure the interoperability between Spring and other AOP frameworks. This module also introduces metadata programming to Spring. Using Spring’s metadata support, we will be able to add annotations to our source code that instruct Spring on where and how to apply aspects.

39.What is JDBC abstraction and DAO module?

Using this module we can keep up the database code clean and simple, and prevent problems that result from a failure to close database resources. A new layer of meaningful exceptions on top of the error messages given by several database servers is bought in this module. In addition, this module uses Spring’s AOP module to provide transaction management services for objects in a Spring application.

40. What are object/relational mapping integration module?

Spring also supports for using of an object/relational mapping (ORM) tool over straight JDBC by providing the ORM module. Spring provide support to tie into several popular ORM frameworks, including Hibernate, JDO, and iBATIS SQL Maps. Spring’s transaction management supports each of these ORM frameworks as well as JDBC.

41.What is web module?

This module is built on the application context module, providing a context that is appropriate for web-based applications. This module also contains support for several web-oriented tasks such as transparently handling multipart requests for file uploads and programmatic binding of request parameters to your business objects. It also contains integration support with Jakarta Struts.

42.What is web module?

Spring comes with a full-featured MVC framework for building web applications. Although Spring can easily be integrated with other MVC frameworks, such as Struts, Spring’s MVC framework uses IoC to provide for a clean separation of controller logic from business objects. It also allows you to decoratively bind request parameters to your business objects. It also can take advantage of any of Spring’s other services, such as I18N messaging and validation.

43.What is a BeanFactory?

A BeanFactory is an implementation of the factory pattern that applies Inversion of Control to separate the application’s configuration and dependencies from the actual application code.

44.What is AOP Alliance?

AOP Alliance is an open-source project whose goal is to promote adoption of AOP and interoperability among different AOP implementations by defining a common set of interfaces and components.

45. What is Spring configuration file?

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.

46.What does a simple spring application contain?

These applications are like any Java application. They are made up of several classes, each performing a specific purpose within the application. But these classes are configured and introduced to each other through an XML file. This XML file describes how to configure the classes, known as the Spring configuration file.

47.What is XMLBeanFactory?

BeanFactory has many implementations in Spring. But one of the most useful one is org.springframework.beans.factory.xml.XmlBeanFactory, which loads its beans based on the definitions contained in an XML file. To create an XmlBeanFactory, pass a to the constructor. The InputStream will provide the XML to the factory. For example, the following code snippet uses a to provide a bean definition XML file to XmlBeanFactory.
BeanFactory factory = new XmlBeanFactory(
new FileInputStream(“beans.xml”));
To retrieve the bean from a BeanFactory, call the getBean() method by passing the name of the bean you want to retrieve.
MyBean myBean = (MyBean) factory.getBean(“myBean”);

48. What are important ApplicationContext implementations in spring framework?

ClassPathXmlApplicationContext – This context loads a context definition from an XML file located in the class path, treating context definition files as class path resources.
FileSystemXmlApplicationContext – This context loads a context definition from an XML file in the filesystem.
XmlWebApplicationContext – This context loads the context definitions from an XML file contained within a web application.

49.Explain Bean lifecycle in Spring framework?

The spring container finds the bean’s definition from the XML file and instantiates the bean.Using the dependency injection, spring populates all of the properties as specified in the bean definition.
If the bean implements the BeanNameAware interface, the factory calls setBeanName() passing the bean’s ID.If the bean implements the BeanFactoryAware interface, the factory calls setBeanFactory(), passing an instance of itself.
If there are any BeanPostProcessors associated with the bean, their post- ProcessBeforeInitialization() methods will be called.If an init-method is specified for the bean, it will be called.
Finally, if there are any BeanPostProcessors associated with the bean, their postProcessAfterInitialization() methods will be called.

50. What is bean wiring?

Combining together beans within the Spring container is known as bean wiring or wiring. When wiring beans, you should tell the container what beans are needed and how the container should use dependency injection to tie them together.

51.How do add a bean in spring application?

<?xml version=”1.0″ encoding=”UTF-8″?>
<bean id=”foo” class=”com.act.Foo”/>
<bean id=”bar” class=”com.act.Bar”/
In the bean tag the id attribute specifies the bean name and the class attribute specifies the fully qualified class name.

52.What are Inner Beans?

When wiring beans, if a bean element is embedded to a property tag directly, then that bean is said to the Inner Bean. The drawback of this bean is that it cannot be reused anywhere else.

53.What are the different types of bean injections?

There are two types of bean injections.
i.By setter
ii.By constructor

54.What is Auto wiring?

You can wire the beans as you wish. But spring framework also does this work for you. It can auto wire the related beans together. All you have to do is just set the autowire attribute of bean tag to an autowire type.
<bean id=”bar” class=”com.act.Foo” Autowire=”autowire type”/>

55.What are different types of Autowire types?

There are four different types by which autowiring can be done.

56.What are the different types of events related to Listeners?

There are a lot of events related to ApplicationContext of spring framework. All the events are subclasses of org.springframework.context.Application-Event. They are

ContextClosedEvent – This is fired when the context is closed.
ContextRefreshedEvent – This is fired when the context is initialized or refreshed.
RequestHandledEvent – This is fired when the web context handles any request.

57.What is an Aspect?

An aspect is the cross-cutting functionality that you are implementing. It is the aspect of your application you are modularizing. An example of an aspect is logging. Logging is something that is required throughout an application. However, because applications tend to be broken down into layers based on functionality, reusing a logging module through inheritance does not make sense. However, you can create a logging aspect and apply it throughout your application using AOP.

58.What is a Jointpoint?

A joinpoint is a point in the execution of the application where an aspect can be plugged in. This point could be a method being called, an exception being thrown, or even a field being modified. These are the points where your aspect’s code can be inserted into the normal flow of your application to add new behavior.

59.What is an Advice?

Advice is the implementation of an aspect. It is something like telling your application of a new behavior. Generally, and advice is inserted into an application at joinpoints.

60.What is a Pointcut?

A pointcut is something that defines at what joinpoints an advice should be applied. Advices can be applied at any joinpoint that is supported by the AOP framework. These Pointcuts allow you to specify where the advice can be applied.

61.What is an Introduction in AOP?

An introduction allows the user to add new methods or attributes to an existing class. This can then be introduced to an existing class without having to change the structure of the class, but give them the new behavior and state.

62.What is a Target?

A target is the class that is being advised. The class can be a third party class or your own class to which you want to add your own custom behavior. By using the concepts of AOP, the target class is free to center on its major concern, unaware to any advice that is being applied.

63.What are singleton beans and how can you create prototype beans?

Beans defined in spring framework are singleton beans. There is an attribute in bean tag named ‘singleton’ if specified true then bean becomes singleton and if set to false then the bean becomes a prototype bean. By default it is set to true. So, all the beans in spring framework are by default singleton beans.
<bean id=”bar” class=”com.act.Foo”

64.What are the important beans lifecycle methods?

There are two important bean lifecycle methods. The first one is setup which is called when the bean is loaded in to the container. The second method is the teardown method which is called when the bean is unloaded from the container.

65.What is a Proxy?

A proxy is an object that is created after applying advice to a target object. When you think of client objects the target object and the proxy object are the same.

66.What is meant by Weaving?

The process of applying aspects to a target object to create a new proxy object is called as Weaving. The aspects are woven into the target object at the specified joinpoints.

67.What are the different points where weaving can be applied?

i.Compile Time
ii.Classload Time

68.What are the different advice types in spring?

Around : Intercepts the calls to the target method
Before : This is called before the target method is invoked
After : This is called after the target method is returned
Throws : This is called when the target method throws and exception
Around : org.aopalliance.intercept.MethodInterceptor
Before : org.springframework.aop.BeforeAdvice
After : org.springframework.aop.AfterReturningAdvice
Throws : org.springframework.aop.ThrowsAdvice

69. How can you override beans default lifecycle methods?

The bean tag has two more important attributes with which you can define your own custom initialization and destroy methods. Here I have shown a small demonstration. Two new methods fooSetup and fooTeardown are to be added to your Foo class.
<bean id=”bar” class=”com.act.Foo”
init-method=”fooSetup” destroy=”fooTeardown”/>

70.What are the different types of AutoProxying?

iii.Metadata autoproxying

71.What is the Exception class related to all the exceptions that are thrown in spring applications?

DataAccessException -org.springframework.dao.DataAccessException

72.What kind of exceptions those spring DAO classes throw?

The spring’s DAO class does not throw any technology related exceptions such as SQLException. They throw exceptions which are subclasses of DataAccessException.

73.What is DataAccessException?

DataAccessException is a RuntimeException. This is an Unchecked Exception. The user is not forced to handle these kinds of exceptions.

74.How JDBC can be used more efficiently in spring framework?

JDBC can be used more efficiently with the help of a template class provided by spring framework called as JdbcTemplate.

75.How do you write data to backend in spring using JdbcTemplate?

The JdbcTemplate uses several of these callbacks when writing data to the database. The usefulness you will find in each of these interfaces will vary. There are two simple interfaces. One is PreparedStatementCreator and the other interface is BatchPreparedStatementSetter.

76. Explain about PreparedStatementCreator?

PreparedStatementCreator is one of the most common used interfaces for writing data to database. The interface has one method createPreparedStatement().
PreparedStatement <strong>createPreparedStatement</strong>(Connection conn) throws SQLException;
When this interface is implemented, we should create and return a PreparedStatement from the Connection argument, and the exception handling is automatically taken care off. When this interface is implemented, another interface SqlProvider is also implemented which has a method called getSql() which is used to provide sql strings to JdbcTemplate.

77.Explain about BatchPreparedStatementSetter?

If the user what to update more than one row at a shot then he can go for BatchPreparedStatementSetter. This interface provides two methods
setValues(PreparedStatement ps, int i) throws SQLException;int getBatchSize();
The getBatchSize() tells the JdbcTemplate class how many statements to create. And this also determines how many times setValues() will be called.

78.Whats the advantages using servlets over using CGI?

Servlets provide a way to generate dynamic documents that is both easier to write and faster to run. Servlets also address the problem of doing server-side programming with platform-specific APIs: they are developed with the Java Servlet API, a standard Java extension.

79.What are the general advantages and selling points of Servlets?

A servlet can handle multiple requests concurrently, and synchronize requests. This allows servlets to support systems such as online
real-time conferencing. Servlets can forward requests to other servers and servlets. Thus servlets can be used to balance load among several servers that mirror the same content, and to partition a single logical service over several servers, according to task type or organizational boundaries.

80.Which package provides interfaces and classes for writing servlets?


81.What’s the Servlet Interface?

The central abstraction in the Servlet API is the Servlet interface. All servlets implement this interface, either directly or, more
commonly, by extending a class that implements it such as HttpServlet.Servlets > Generic Servlet > HttpServlet > MyServlet.
The Servlet interface declares, but does not implement, methods that manage the servlet and its communications with clients. Servlet writers provide some or all of these methods when developing a servlet.

82.When a servlet accepts a call from a client, it receives two objects. What are they?

ServletRequest (which encapsulates the communication from the client to the server) and ServletResponse (which encapsulates the communication from the servlet back to the client). ServletRequest and ServletResponse are interfaces defined inside javax.servlet package.

83.What information does ServletRequest allow access to?

Information such as the names of the parameters passed in by the client, the protocol (scheme) being used by the client, and the namesof the remote host that made the request and the server that received it.
Also the input stream, as ServletInputStream.Servlets use the input stream to get data from clients that use application protocols such as the HTTP POST and GET methods.

84.What type of constraints can ServletResponse interface set on the client?

It can set the content length and MIME type of the reply. It also provides an output stream, ServletOutputStream and a Writer through which the servlet can send the reply data.

85.Explain servlet lifecycle?

Each servlet has the same life cycle: first, the server loads and initializes the servlet (init()), then the servlet handles zero or more client requests (service()), after that the server removes the servlet (destroy()). Worth noting that the last step on some servers is done when they shut down.How does HTTP Servlet handle client requests?
An HTTP Servlet handles client requests through its service method. The service method supports standard HTTP client requests by dispatching each request to a method designed to handle that request.

86.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.

87.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.

88.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.

89.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.

90.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.

91.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.

92.What are container services?

A container is a runtime support of a system-level entity. Containers provide components with services such as lifecycle management, security, deployment, and threading.

93.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.

94.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.

95.What is Applet container?

Manages the execution of applets. Consists of a Web browser and Java Plugin running on the client together.

96.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.

97.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.

98.What are types of J2EE clients?

Following are the types of J2EE clients:
2. application clients
3. Java Web Start-enabled rich clients, powered by Java Web Start technology.
4. Wireless clients, based on Mobile Information Device Profile (MIDP) technology.

99.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 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.

100.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.

101.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 naming and directory services, including existing naming and
directory services such as LDAP, NDS, DNS, and NIS.

102.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.

103.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.

104.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.

105.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.

106.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.

107.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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