JSP Interview Questions

Question: What is JSP?
Answer: JavaServer Pages (JSP) technology is the Java platform technology for delivering dynamic content to web clients in a portable, secure and well-defined way. The JavaServer Pages specification extends the Java Servlet API to provide web application developers

Question: What is the role of JSP in MVC Model?
Answer: JSP is mostly used to develop the user interface, It plays are role of View in the MVC Model.

Question: What do you understand by context initialization parameters?
Answer: The context-param element contains the declaration of a web application's servlet context initialization parameters.

name
value


The Context Parameters page lets you manage parameters that are accessed through the ServletContext.getInitParameterNames and ServletContext.getInitParameter methods.

Question: Can you extend JSP technology?
Answer: JSP technology lets the programmer to extend the jsp to make the programming more easier. JSP can be extended and custom actions and tag libraries can be developed.

Question: What do you understand by JSP translation?
Answer: JSP translators generate standard Java code for a JSP page implementation class. This class is essentially a servlet class wrapped with features for JSP functionality.

Question: What you can stop the browser to cash your page?
Answer: Instead of deleting a cache, you can force the browser not to catch the page.
<%
response.setHeader("pragma","no-cache");//HTTP 1.1
response.setHeader("Cache-Control","no-cache");
response.setHeader("Cache-Control","no-store");
response.addDateHeader("Expires", -1);
response.setDateHeader("max-age", 0);
//response.setIntHeader ("Expires", -1); //prevents caching at the proxy server
response.addHeader("cache-Control", "private");

%>
put the above code in your page.

Question: What you will handle the runtime exception in your jsp page?
Answer: The errorPage attribute of the page directive can be used to catch run-time exceptions automatically and then forwarded to an error processing page.

For example:
<%@ page errorPage="customerror.jsp" %>
above code forwards the request to "customerror.jsp" page if an uncaught exception is encountered during request processing. Within "customerror.jsp", you must indicate that it is an error-processing page, via the directive: <%@ page isErrorPage="true" %>.

Struts Interview Questions

Q: How you will make available any Message Resources Definitions file to the Struts Framework Environment?
A: Message Resources Definitions file are simple .properties files and these files contains the messages that can be used in the struts project. Message Resources Definitions files can be added to the struts-config.xml file through tag.
Example:



Q: What is Action Class?
A: The Action is part of the controller. The purpose of Action Class is to translate the HttpServletRequest to the business logic. To use the Action, we need to Subclass and overwrite the execute() method. The ActionServlet (commad) passes the parameterized class to Action Form using the execute() method. There should be no database interactions in the action. The action should receive the request, call business objects (which then handle database, or interface with J2EE, etc) and then determine where to go next. Even better, the business objects could be handed to the action at runtime (IoC style) thus removing any dependencies on the model. The return type of the execute method is ActionForward which is used by the Struts Framework to forward the request to the file as per the value of the returned ActionForward object.


Q: Write code of any Action Class?
A: Here is the code of Action Class that returns the ActionForward object.
TestAction.java
package roseindia.net;

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");
}
}
Q: What is ActionForm?
A: 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.


Q: What is Struts Validator Framework?
A: Struts Framework provides the functionality to validate the form data. It can be use to validate the data on the users browser as well as on the server side. Struts Framework emits the java scripts and it can be used validate the form data on the client browser. Server side validation of form can be accomplished by sub classing your From Bean with DynaValidatorForm class.

The Validator framework was developed by David Winterfeldt as third-party add-on to Struts. Now the Validator framework is a part of Jakarta Commons project and it can be used with or without Struts. The Validator framework comes integrated with the Struts Framework and can be used without doing any extra settings.


Q. Give the Details of XML files used in Validator Framework?
A: The Validator Framework uses two XML configuration files validator-rules.xml and 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.

Q. How you will display validation fail errors on jsp page?
A: Following tag displays all the errors:



Q. How you will enable front-end validation based on the xml in validation.xml?
A: The tag to allow front-end validation based on the xml in validation.xml. For example the code: generates the client side java script for the form "logonForm" as defined in the validation.xml file. The when added in the jsp file generates the client site validation script.

Core Java Interview Question

Question: What's the difference between an interface and an abstract class?

Answer: An abstract class may contain code in method bodies, which is not allowed in an interface. With abstract classes, you have to inherit your class from it and Java does not allow multiple inheritance. On the other hand, you can implement multiple interfaces in your class.

Question: Why would you use a synchronized block vs. synchronized method?

Answer: Synchronized blocks place locks for shorter periods than synchronized methods.

Question: Explain the usage of the keyword transient?

Answer: This keyword indicates that the value of this member variable does not have to be serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (i.e. zero for integers).

Question: How can you force garbage collection?

Answer: You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately.


Question: How do you know if an explicit object casting is needed?

Answer: If you assign a superclass object to a variable of a subclass's data type, you need to do explicit casting. For example:

Object a; Customer b; b = (Customer) a;

When you assign a subclass to a variable having a supeclass type, the casting is performed automatically.

Question: What's the difference between the methods sleep() and wait()

Answer: The code sleep(1000); puts thread aside for exactly one second. The code wait(1000), causes a wait of up to one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.

Question: Can you write a Java class that could be used both as an applet as well as an application?

Answer: Yes. Add a main() method to the applet.

Question: What's the difference between constructors and other methods?

Answer: Constructors must have the same name as the class and can not return a value. They are only called once while regular methods could be called many times.

Question: Can you call one constructor from another if a class has multiple constructors

Answer: Yes. Use this() syntax.

Question: Explain the usage of Java packages.

Answer: This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Packages access level also allows you to protect data from being used by the non-authorized classes.

Question: If a class is located in a package, what do you need to change in the OS environment to be able to use it?

Answer: You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:\dev\com\xyz\hr\Employee.java. In this case, you'd need to add c:\dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:

c:\>java com.xyz.hr.Employee

Question: What's the difference between J2SDK 1.5 and J2SDK 5.0?

Answer: There's no difference, Sun Microsystems just re-branded this version.

Question: What would you use to compare two String variables - the operator == or the method equals()?
Answer: I'd use the method equals() to compare the values of the Strings and the == to check if two variables point at the same instance of a String object.

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