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What happens under the hood?
User
Request
Web Server/
Servlet Engine
JSP Handler Servlet
(Page Compilation Servlet)
New or
modified file?
Compile into
Servlet
Execute
Servlet
Yes
No
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Various Elements in a JSP
Directives
page
Defines information that will be globally available for a
JSP
include
Used to insert text and code at JSP translation time
taglib
Defines a mechanism for extending the current set of
JSP tags
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Different Attributes of the
Page Directive
Attribute Definition
language =
”<scriptingLanguage>”
This attribute tells the server about the language to be
used to complete the JSP file. At present, Java is the only
language that can be used.
extends =
”<className>"
This attribute defines the parent class that the generated
servlet will extend.
import =
”<importList>"
This attribute defines the list of packages that will be
available to this JSP. However, a comma must separate
each package.
session = "true | false" This attribute determines whether the session data will be
available to this page. The default is true.
buffer = "none | <size
in kb>"
This attribute determines whether the output stream is
buffered. The default value is 8 kb.
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Different Attributes of the
Page Directive – (1)
Attribute Definition
autoFlush = "true |
false"
Determines whether the output buffer will be flushed
automatically, or whether it will raise an exception
when the buffer is full. The default is true.
isThreadSafe = "true
| false"
Specifies whether page can service more than one
request at a time. The default is true.
info = ”<text>" Specifies information about the JSP, can be accessed
by Servlet.getServletInfo().
errorPage =
”<error_URL>"
This attribute represents the relative URL to the JSP
that will handle exceptions.
isErrorPage = "true |
false"
This attribute states whether or not the JSP is an
errorPage. The default is false.
contentType =
”<ctinfo>"
This attribute represents the MIME type and
character set of the response.
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Using page Attributes - An
example
<%@ page language = "java"
import = "java.rmi.*, java.util.*"
session = "true"
buffer = "12kb"
autoFlush = "true"
info = "page directive jsp"
errorPage = "Error.jsp"
isErrorPage = "false"
isThreadSafe = "false" %>
<HTML> <TITLE> JSP Elements </TITLE>
<HEAD> <H1> JSP Elements </H1> </HEAD>
<BODY> </BODY> </HTML>
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More on Directives
include directive
Syntax
<%@ include file = “relativeURLspec” %>
taglib directive
Syntax
<%@ taglib uri = “tagLibraryURI”
prefix = “tagPrefix” %>
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Some Important Points
While using directives, remember the
following:
Directives are messages to the JSP container, that is, the
JSP engine
Directives do not store any results in the output buffer
Directives are processed when the JSP is initialized
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JSP Scripting Elements
Expressions
Scriptlets
Declarations
Scripting is a mechanism for embedding
code fragments directly in an HTML page.
The following three scripting elements are
involved in JSP scripting:
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JSP Scripting Elements – (1)
Expressions are evaluated to produce a
java.lang.String type result.
Evaluated to
produce 4
<HTML>
<BODY> 2 + 2 equals <%= 2 + 2 %>
</BODY>
</HTML>
Example:
Syntax: <%= expression %>
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JSP Scripting Elements – (2)
Scriptlets contain code that is valid for the
language specified in the language directive. Java
is the only language that is presently available.
Scriptlet
<HTML> <BODY>
<% out.println("HELLO WORLD!!"); %>
</BODY> </HTML>
Example:
Syntax: <% scriptlet_source; %>
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