Jsp interview Questions And Answers

leoraja8 · #1 (**permalink**) 09-04-2007, 03:46 AM

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 uninterpreted 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


Example 1


Displays in the page source:

leoraja8 · #2 (**permalink**) 09-04-2007, 03:47 AM

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" %>
<html>
<head><title>A Hidden Comment </title></head>
<body>
<%-- This comment will not be visible to the colent in the page source --%>
</body>
</html>

leoraja8 · #3 (**permalink**) 09-04-2007, 03:48 AM

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

leoraja8 · #4 (**permalink**) 09-04-2007, 03:48 AM

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; %>

leoraja8 · #5 (**permalink**) 09-04-2007, 03:49 AM

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.

leoraja8 · #6 (**permalink**) 09-04-2007, 03:50 AM

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

leoraja8 · #7 (**permalink**) 09-04-2007, 03:50 AM

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.

leoraja8 · #8 (**permalink**) 09-04-2007, 03:51 AM

What are the different scope valiues for the <jsp:useBean>?

The different scope values for <jsp:useBean> are

1. page
2. request
3.session
4.application

leoraja8 · #9 (**permalink**) 09-04-2007, 03:52 AM

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. Hte 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 n the servlet instance.

leoraja8 · #10 (**permalink**) 09-04-2007, 03:53 AM

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
%>

amansundar · #11 (**permalink**) 09-11-2007, 06:14 AM

hi raja,
thank you for posting some important question in jsp.which are
very helpfull to me.... it would be better if you post those questions as an article....

sathian · #12 (**permalink**) 12-15-2007, 12:39 AM

Response has already been commited error. What does it mean?

This error show only when you try to redirect a page after you already have written something in your page. This happens because HTTP specification force the header to be set up before the lay out of the page can be shown (to make sure of how it should be displayed, content-type=”text/html” or “text/xml” or “plain-text” or “image/jpg”, etc.) When you try to send a redirect status (Number is line_status_402), your HTTP server cannot send it right now if it hasn’t finished to set up the header. If not starter to set up the header, there are no problems, but if it ’s already begin to set up the header, then your HTTP server expects these headers to be finished setting up and it cannot be the case if the stream of the page is not over… In this last case it’s like you have a file started with <HTML Tag><Some Headers><Body>some output (like testing your variables.) Before you indicate that the file is over (and before the size of the page can be setted up in the header), you try to send a redirect status. It s simply impossible due to the specification of HTTP 1.0 and 1.1

Thanks
Sathian.K

sathian · #13 (**permalink**) 12-15-2007, 12:40 AM

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.

Thanks
Sathian.K

sathian · #14 (**permalink**) 12-15-2007, 12:41 AM

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 <%! DECLARE %>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

Thanks
Sathian.K

sathian · #15 (**permalink**) 12-15-2007, 12:42 AM

How many types of JDBC Drivers are present and what are they?

There are 4 types of JDBC Drivers

* JDBC-ODBC Bridge Driver
* Native API Partly Java Driver
* Network protocol Driver
* JDBC Net pure Java Driver

Thanks
Sathian.K

sathian · #16 (**permalink**) 12-15-2007, 12:44 AM

What are the implicit objects?

Implicit objects are objects that are created by the web container and contain information related to a particular request, page, or application. They are: request, response, pageContext, session, application, out, config, page, exception.

Thanks
Sathian.K

sathian · #17 (**permalink**) 12-15-2007, 12:48 AM

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 uninterpreted 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


Thanks
Sathian.K

sathian · #18 (**permalink**) 12-15-2007, 12:49 AM

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 --%>

Thanks
Sathian.K

shaalini · #19 (**permalink**) 12-23-2007, 09:13 PM

What is the difference between <jsp:include page = ... > and
<%@ include file = ... >?

Both the tag includes the information from one page in another. The differences are as follows:
<jsp:include page = ... >: This is like a function call from one jsp to another jsp. It is executed ( the included page is executed and the generated html content is included in the content of calling jsp) each time the client page is accessed by the client. This approach is useful to for modularizing the web application. If the included file changed then the new content will be included in the output.

<%@ include file = ... >: In this case the content of the included file is textually embedded in the page that have <%@ include file=".."> directive. In this case in the included file changes, the changed content will not included in the output. This approach is used when the code from one jsp file required to include in multiple jsp files.

shaalini · #20 (**permalink**) 12-23-2007, 09:14 PM

What is the difference between <jsp:forward page = ... > and
response.sendRedirect(url)?

The <jsp:forward> element forwards the request object containing the client request information from one JSP file to another file. The target file can be an HTML file, another JSP file, or a servlet, as long as it is in the same application context as the forwarding JSP file.
sendRedirect sends HTTP temporary redirect response to the browser, and browser creates a new request to go the redirected page. The response.sendRedirect kills the session variables.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
PHP Interview Questions & Answers	H2o	Interview Questions & Answers and Tips	102	04-07-2008 07:26 AM
ASP.NET 2.0 Interview Questions And Answers	S.Vinothkumar	Interview Questions & Answers and Tips	150	01-11-2008 02:14 AM
CSS Interview Questions And Answers	Sabari	Interview Questions & Answers and Tips	137	11-25-2007 09:38 PM
HR Interview Questions with Answers	Sabari	Interview Questions & Answers and Tips	63	11-23-2007 06:13 AM
.Net Interview Questions & Answers	Venkat	Interview Questions & Answers and Tips	100	11-13-2007 06:55 AM