|
| |
| 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 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
<!-- comment [ <%= expression %>
] -->
Example 1
<!-- This is a commnet sent to client
on
<%= (new java.util.Date()).toLocaleString()
%>
-->
Displays in the page source:
<!-- This is a commnet
sent to client on January 24, 2004 --> |
| |
|
| Q: |
What
is a Hidden Comment? |
| A: |
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>
|
| |
|
| Q: |
What
is a Expression? |
| A: |
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 |
| |
|
| Q: |
What
is a Declaration?
|
| A: |
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; %> |
| |
|
| Q: |
What
is a Scriptlet?
|
| A: |
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. |
| |
|
| Q: |
What
are implicit objects? List them? |
| 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 re listed below
- request
- response
- pageContext
- session
- application
- out
- config
- page
- exception
|
|
| |
|
| Q: |
Difference
between forward and sendRedirect? |
| A: |
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. |
| |
|
| Q: |
What
are the different scope valiues for the
<jsp:useBean>? |
| A: |
The
different scope values for <jsp:useBean>
are
1.
page
2. request
3.session
4.application
|
| |
|
| Q: |
Explain
the life-cycle mehtods in JSP? |
| A: |
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. |
| |
|
|
|
