Q What is the difference between JSP and Servlets ?
A
JSP
is used mainly for presentation only. A JSP can only be HttpServlet
that means the only supported protocol in JSP is HTTP. But a servlet can
support any protocol like HTTP, FTP, SMTP etc.
2 Q What is difference between custom JSP tags and beans?
A
Custom
JSP tag is a tag you defined. You define how a tag, its attributes and
its body are interpreted, and then group your tags into collections
called tag libraries that can be used in any number of JSP files. To use
custom JSP tags, you need to define three separate components: the tag
handler class that defines the tag's behavior ,the tag library
descriptor file that maps the XML element names to the tag
implementations and the JSP file that uses the tag library
JavaBeans are Java utility classes you defined. Beans have a standard format for Java classes. You use tags
Custom
tags and beans accomplish the same goals -- encapsulating complex
behavior into simple and accessible forms. There are several
differences:
Custom
tags can manipulate JSP content; beans cannot. Complex operations can
be reduced to a significantly simpler form with custom tags than with
beans. Custom tags require quite a bit more work to set up than do
beans. Custom tags usually define relatively self-contained behavior,
whereas beans are often defined in one servlet and used in a different
servlet or JSP page. Custom tags are available only in JSP 1.1 and
later, but beans can be used in all JSP 1.x versions.
3 Q What are the different ways for session tracking?
A
Cookies, URL rewriting, HttpSession, Hidden form fields
4 Q What mechanisms are used by a Servlet Container to maintain session information?
A
Cookies, URL rewriting, and HTTPS protocol information are used to maintain session information
5 Q Difference between GET and POST
A
In
GET your entire form submission can be encapsulated in one URL, like a
hyperlink. query length is limited to 255 characters, not secure,
faster, quick and easy. The data is submitted as part of URL.
In POST data is submitted inside body of the HTTP request. The data is not visible on the URL and it is more secure.
6 Q What is session?
A
The
session is an object used by a servlet to track a user's interaction
with a Web application across multiple HTTP requests. The session is
stored on the server.
7 Q What is servlet mapping?
A
The servlet mapping defines an association between a URL pattern and a servlet. The mapping is used to map requests to Servlets.
8 Q What is servlet context ?
A
The
servlet context is an object that contains a information about the Web
application and container. Using the context, a servlet can log events,
obtain URL references to resources, and set and store attributes that
other servlets in the context can use.
9 Q What is a servlet ?
A
servlet is a java program that runs inside a web container.
10 Q Can we use the constructor, instead of init(), to initialize servlet?
A
Yes.
But you will not get the servlet specific things from constructor. The
original reason for init() was that ancient versions of Java couldn’t
dynamically invoke constructors with arguments, so there was no way to
give the constructor a ServletConfig. That no longer applies, but
servlet containers still will only call your no-arg constructor. So you
won’t have access to a ServletConfig or ServletContext.
12 Q How many JSP scripting elements are there and what are they?
A
There are three scripting language elements: declarations, scriptlets, expressions.
13 Q How do I include static files within a JSP page?
A
Static
resources should always be included using the JSP include directive.
This way, the inclusion is performed just once during the translation
phase.
14 Q How can I implement a thread-safe JSP page?
A
You can make your JSPs thread-safe adding the directive <%@ page isThreadSafe="false" % > within your JSP page.
15 Q What is the difference in using request.getRequestDispatcher() and context.getRequestDispatcher()?
A
In
request.getRequestDispatcher(path) in order to create it we need to
give the relative path of the resource. But
in context.getRequestDispatcher(path) in order to create it we need to
give the absolute path of the resource.
16 Q What are the lifecycle of JSP?
A
When presented with JSP page the JSP engine does the following 7 phases.
Page translation: -page is parsed, and a java file which is a servlet is created.
Page compilation: page is compiled into a class file
Page loading : This class file is loaded.
Create an instance :- Instance of servlet is created
jspInit() method is called
_jspService is called to handle service calls
_jspDestroy is called to destroy it when the servlet is not required.
17 Q What are context initialization parameters?
A
Context
initialization parameters are specified by the <context-param> in
the web.xml file, these are initialization parameter for the whole
application.
Q How to get the context parameters and servlet init parameters?
To get the context param:
ServletContext application = getServletConfig().getServletContext();
String xxx = application.getInitParameter(“xxx”);
To get the servlet init parameter:
Enumeration enumeration = getServletConfig().getInitParameterNames();
while(enumeration.hasMoreElements()){
pw.print(enumeration.nextElement() + " ");
}
while(enumeration.hasMoreElements()){
pw.print(enumeration.nextElement() + " ");
}
18 Q What is a Expression?
A
Expressions
are act as place holders for language expression, expression is
evaluated each time the page is accessed. This will be included in the
service method of the generated servlet.
19 Q What is a Declaration?
A
It
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 semicolons separate them.
The declaration must be valid in the scripting language used in the JSP
file. This will be included in the declaration section of the generated
servlet.
20 Q What is a Scriptlet?
A
A
scriptlet can contain any number of language statements, variable or
expressions that are valid in the page scripting language. Within
scriptlet tags, you can declare variables to use later in the file,
write expressions valid in the page scripting language, use any of the
JSP implicit objects or any object declared with a
<jsp:useBean>. Generally a scriptlet can contain any java code
that are valid inside a normal java method. This will become the part of
generated servlet's service method.
21 Q What are the implicit objects?
A
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 are: request, response,
pageContext, session, application, out, config, page, exception
22 Q What's the difference between forward and sendRedirect?
A
forward
is server side redirect and sendRedirect is client side redirect. 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 completely with in
the web container And then returns to the calling method. When a
sendRedirect 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 completely 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. Client can disable
sendRedirect.
23 Q What are the different scopes available ?
A page, request, session, application
24 Q Is JSP extensible ?
A
Yes,
it is. JSP technology is extensible through the development of custom
actions, or tags, which are encapsulated in tag libraries.
25 Q What's the Servlet Interface?
A
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.
26 Q What are two different types of Servlets ?
A
GenericServlet
and HttpServlet. HttpServlet is used to implement HTTP protocol, where
as Generic servlet can implement any protocol.
27 Q What is the life cycle of servlet?
A
Each
servlet has the same life cycle: first, the server loads and
initializes the servlet by calling the init method. This init() method
will be executed only once during the life time of a servlet. Then when a
client makes a request, it executes the service method. finally it
executes the destroy() method when server removes the servlet.
28 Q Can we call destroy() method on servlets from service method ?
A Yes.
29 Q What is the need of super.init (config) in servlets ?
A
Then
only we will be able to access the ServletConfig from our servlet. If
there is no ServletConfig our servlet will not have any servlet nature.
32 Q Can we write a constructor for servlet ?
Yes.
But the container will always call the default constructor only. If
default constructor is not present , the container will throw an
exception.
33 Q What is the difference between <%@ include ...> (directive include) and <jsp:include> ?
A
@
include is static include. It is inline inclusion. The contents of the
file will get included on Translation phase. It is something like inline
inclusion. We cannot have a dynamic filename for directive include.
<jsp:include> is dynamic include. Here the included file will be
processed as a separate file and the response will be included. We can
have a dynamic filename for <jsp:include>. We can aslo pass
parameters to <jsp:include
34 Q Can I just abort processing a JSP?
A
Yes. You can put a return statement to abort JSP processing.
35 Q What are the parameters for service method ?
A ServletRequest and ServletResponse
36 Q What are cookies ?
A
Cookies are small textual information that are stored on client computer. Cookies are used for session tracking.
37 Q How do I prevent the output of my JSP or Servlet pages from being cached by the browser?
A
By setting appropriate HTTP header attributes we can prevent caching by the browser
<%
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
38 Q How to refer the "this" variable within a JSP page?
A
Under
JSP 1.0, the page implicit object page is equivalent to "this", and
returns a reference to the servlet generated by the JSP page.
39 Q How many JSP scripting elements and what are they?
A
There are three scripting elements in JSP . They are declarations, scriptlets, expressions.
40 Q Can we implement an interface in JSP ?
A No.
41 Q What is the meaning of response has already been committed error?
A
You
will get this error only when you try to redirect a page after you
already have flushed the output buffer. This happens because HTTP
specification force the header to be set up before the lay out of the
page can be shown. When you try to send a redirect status, your HTTP
server cannot send it right now if it hasn't finished to set up the
header. Simply it is giving the error due to the specification of HTTP
1.0 and 1.1
42 Q How do I use a scriptlet to initialize a newly instantiated bean?
A
A
jsp:useBean action may optionally have a body. If the body is
specified, its contents will be automatically invoked when the specified
bean is instantiated (Only at the time of instantiation.) Typically,
the body will contain scriptlets or jsp:setProperty tags to initialize
the newly instantiated bean, although you are not restricted to using
those alone.
43 Q What is JSP?
A
JSP
is a server side scripting technology. JSP allows Java as well as a few
special tags to be embedded into a web file (HTML/XML, etc). The suffix
must ends with .jsp.
44 Q What are JSP Actions?
A
JSP
actions use constructs in XML syntax to control the behavior of the
servlet engine. You can dynamically insert a file, reuse JavaBeans
components, forward the user to another page, or generate HTML for the
Java plugin. Available actions include: jsp:include, jsp:useBean,
jsp:setProperty, jsp:getProperty, jsp:forward and Jsp: plugin
45 Q What is the difference between ServletContext and ServletConfig?
A
The
ServletConfig gives the information about the servlet initialization
parameters. The servlet engine implements the ServletConfig interface in
order to pass configuration information to a servlet. The server passes
an object that implements the ServletConfig interface to the servlet's
init() method.
The
ServletContext gives information about the container. The
ServletContext interface provides information to servlets regarding the
environment in which they are running. It also provides standard way for
servlets to write events to a log file.
46 Q How can a servlet refresh automatically?
A We can use a client-side Refresh or Server Push
47 Q What is Server side push?
A
Server
Side push is useful when data needs to change regularly on the clients
application or browser, without intervention from client. The mechanism
used is, when client first connects to Server, then Server keeps the
TCP/IP connection open.
48 Q What is client side refresh?
A
The
standard HTTP protocols ways of refreshing the page, which is normally
supported by all browsers. <META HTTP-EQUIV="Refresh" CONTENT="5;
URL=/servlet/MyServlet/"> This will refresh the page in the browser
automatically and loads the new data every 5 seconds.
49 Q What is the Max amount of information that can be saved in a Session Object ?
A
There
is no such limit on the amount of information that can be saved in a
Session Object. The only limit is the Session ID length , which should
not exceed more than 4K.
50 Q Why should we go for inter servlet communication?
A
The
three major reasons to use inter servlet communication are: a) Direct
servlet manipulation - allows to gain access to the other currently
loaded servlets and perform certain tasks (through the ServletContext
object) b) Servlet reuse - allows the servlet to reuse the public
methods of another servlet. c) Servlet collaboration - requires to
communicate with each other by sharing specific information (through
method invocation)
51 Q What is a output comment?
A
A
comment that is sent to the client in the viewable page source. The JSP
engine handles an output comment as un interpreted 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.
52 Q What is a Hidden Comment
A
Hidden
Comments are JSP comments. 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.
53 Q What are the differences between a session and a cookie?
A
Session
is stored in server but cookie stored in client. Session should work
regardless of the settings on the client browser. There is no limit on
the amount of data that can be stored on session. But it is limited in
cookie. Session can store objects and cookies can store only strings.
Cookies are faster than session.
54 Q What is HttpTunneling?
A
HTTP
tunneling is used to encapsulate other protocols within the HTTP or
HTTPS protocols. Normally the intranet is blocked by a firewall and the
network is exposed to the outer world only through a specific web server
port, that listens for only HTTP requests. To use any other protocol,
that by passes the firewall, the protocol is embedded in HTTP and send
as HttpRequest.
55 Q How to pass information from JSP to included JSP?
A By using <jsp:param> tag.
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