JSP Interview Questions and Answers

What is a output comment?

A comment that is sent to the client in the viewable page source. The JSP engine handles an output comment as uninterrupted HTML text, returning the
comment in the HTML output sent to the client. You can see the comment by viewing the page source from your Web browser.

JSP Syntax
<!-- comment [ <%= expression %> ] -->
or
<!-- This is a comment sent to client on
<%= (new java.util.Date()).toLocaleString() %>   -->

What is a Hidden Comment?

A Comments that documents the JSP page but is not sent to the client. The JSP engine ignores a hidden comment, and does not process any code within hidden comment tags. A hidden comment is not sent to the client, either in the displayed JSP page or the HTML page source.

The hidden comment is useful when you want to hide or comment out part of your JSP page. You can use any characters in the body of the comment except the closing --%> combination. If you need to use --%> in your comment, you can escape it by typing --%>.

JSP Syntax :

<%-- comment --%> Examples <%@ page language="java" %>

A Hidden Comment

<%-- This comment will not be visible to the colent in the page source --%>

What is a Expression?

An expression tag contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the JSP file. Because the value of an expression is converted to a String, you can use an expression within text in a JSP file. Like
<%= someexpression %> 
<%= (new java.util.Date()).toLocaleString() %>
You cannot use a semicolon to end an expression 

What is a Declaration?

A declaration declares one or more variables or methods for use later in the JSP source file. 
A declaration must contain at least one complete declarative statement. You can declare any number of variables or methods within one declaration tag, as long as they are separated by semicolons. The declaration must be valid in the scripting language used in the JSP file. 
<%! somedeclarations %>
<%! int i = 0; %>
<%! int a, b, c; %>

What is a Scriptlet?

A scriptlet can contain any number of language statements, variable or method declarations, or expressions that are valid in the page scripting language.Within scriptlet tags, you can 
1.Declare variables or methods to use later in the file (see also Declaration). 
2.Write expressions valid in the page scripting language (see also Expression). 
3.Use any of the JSP implicit objects or any object declared with a <jsp:useBean> tag. 
You must write plain text, HTML-encoded text, or other JSP tags outside the scriptlet. 
Scriptlets are executed at request time, when the JSP engine processes the client request. If the scriptlet produces output, the output is stored in the out object, from which you can display it 

What are implicit objects? List them?

Certain objects that are available for the use in JSP documents without being declared first. These objects are parsed by the JSP engine and inserted into the generated servlet. The implicit objects re listed below
request
response
pageContext
session
application
out
config
page
exception

Difference between forward and sendRedirect?

When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completly with in the web container.

When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completly new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.

What are the different scope valiues for the ?

The different scope values for <jsp:useBean> are 
1. page
2. request
3. session
4. application

Explain the life-cycle mehtods in JSP?

The generated servlet class for a JSP page implements the HttpJspPage interface of the javax.servlet.jsp package. HttpJspPage interface extends the JspPage interface which inturn extends the Servlet interface of the javax.servlet package. the generated servlet class thus implements all the methods of the these three interfaces. The JspPage interface declares only two mehtods - jspInit() and jspDestroy() that must be implemented by all JSP pages regardless of the client-server protocol. However the JSP specification has provided the HttpJspPage interfaec specifically for the JSp pages serving HTTP requests. This interface declares one method _jspService(). 
The jspInit()- The container calls the jspInit() to initialize te servlet instance.It is called before any other method, and is called only once for a servlet instance. 
The _jspservice()- The container calls the _jspservice() for each request, passing it the request and the response objects. 
The jspDestroy()- The container calls this when it decides take the instance out of service. It is the last method called in the servlet instance

How do I prevent the output of my JSP or Servlet pages from being cached by the browser?

You will need to set the appropriate HTTP header attributes to prevent the dynamic content output by the JSP page from being cached by the browser. Just execute the following scriptlet at the beginning of your JSP pages to prevent them from being cached at the browser. You need both the statements to take care of some of the older browser versions.

<% response.setHeader("Cache-Control","no-store"); //HTTP 1.1

response.setHeader("Pragma","no-cache"'); //HTTP 1.0

response.setDateHeader ("Expires", 0);  //prevents caching at the proxy server

%>

How does JSP handle run-time exceptions?

You can use the errorPage attribute of the page directive to have uncaught run-time exceptions automatically forwarded to an error processing page. For example: <%@ page errorPage='error.jsp' %> redirects the browser to the JSP page error.jsp if an uncaught exception is encountered during request processing. Within error.jsp, if you indicate that it is an error-processing page, via the directive: <%@ page isErrorPage='true' %> Throwable object describing the exception may be accessed within the error page via the exception implicit object. Note: You must always use a relative URL as the value for the errorPage attribute.

How can I implement a thread-safe JSP page? What are the advantages and Disadvantages of using it?

You can make your JSPs thread-safe by having them implement the SingleThreadModel interface. This is done by adding the directive <%@ page isThreadSafe='false' %> within your JSP page. With this, instead of a single instance of the servlet generated for your JSP page loaded in memory, you will have N instances of the servlet loaded and initialized, with the service method of each instance effectively synchronized. You can typically control the number of instances (N) that are instantiated for all servlets implementing SingleThreadModel through the admin screen for your JSP engine. More importantly, avoid using the tag for variables. If you do use this tag, then you should set isThreadSafe to true, as mentioned above. Otherwise, all requests to that page will access those variables, causing a nasty race condition. SingleThreadModel is not recommended for normal use. There are many pitfalls, including the example above of not being able to use <%! %>. You should try really hard to make them thread-safe the old fashioned way: by making them thread-safe .

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General Knowledge of India

In 1897, the Birsa Movement supporters raised which colour flag as a symbol of Birsa Raj?

Ratio and Proportion

The cost of 10 books is Rs. 80/-. Find the value of 15 books?

The cost of 48 bags of paddy is Rs. 16,800/-. What is the cost of 36 bags of paddy?

Monthly expenditure of a family of 4 members is Rs 2800/-. What is the expenditure if there are 3 members in the family?

Annual incomes of the families of Sita and Latha are in the ratio 4:3 and their annual expenditure are in the ratio 3:2. What is their annual income if they save Rs. 3000/- in a year?

A certain sum of money is divided between A and B in the ratio of 5/4 : 5/3 and A got Rs. 360/-. Find the total sum of money and B’s share?

In an office, the ratio of the salaries of an officer and a clerk is 15:7. If the salary of a clerk is Rs. 720/- less than the salary of the officer, find the salary of each?

In an election to a municipal council, the votes secured by two candidates are in the ratio 13:19. The elected candidates gets 312 votes more than the second candidate. How many votes are secured by the second candidate?

A certain sum of money is divided between Murthy and Prasad in the ratio 22/7 : 8/3. If Murthy gets Rs. 120/- more than Prasad, find the share of each?

In a cricket test series, the runs made by Raju and Tendulkar are in the ratio 5:9 and Tendulkar and Azar are in the ratio 6:7. What are the runs made by them if Azar makes 187 runs more than Raju?

If A:B = 2:3 and B:C = 9:5 find A:B:C?

If A:B = 3/5:5/7 and B:C = 3/4:2/5, find A:B:C?

If R:S = 0.01:0.11 and S:T = 2.2:1, Find R:S:T?

In a school, Under a Saving Scheme, Rekha saves 3/2 times the savings of Bindu, Geeta saves 4 times the savings of Rekha. Find the ratio of the savings of all the three in least terms?

Simplification

A man left 1/3 rd of his property to his wife and 3/5 th of the remainder to his daughter. He gave the rest to his son who received Rs. 6400/-. How much was his original property worth?

Ratio and Proportion

In a school 4/9 of the pupils are boys. There are 125 girls. How many boys are there?

If A:B = 3:4 and B:C = 5:6, find A:C?

IF X:Y = 3:4 AND Y:Z = 4:5, FIND X:Y:Z?