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Developing JavaServer Pages
Think Possibility
JSP Technology
• JavaServer Pages (JSP) enable you to write standard
HTML pages contaning tags that run powerful programs
based on the Java programming language.
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Hello Servlet Code
public void generateResponse(HttpServletRequest request,
HttpServletResponse response) throws IOException {
// Determine the specified name (or use default) String name =
request.getParameter("name"); if ( (name == null) || (name.length() ==0) ) { name =
DEFAULTJSTAME;
// Specify the content type is HTML response.setContentType("text/html"); PrintWriter out
= response.getWriter();
// Generate the HTML response
out.printIn("<HTML>");
out.println("<HEAD>");
out.println("<TITLE>Hello Servlet</TITLE>");
out.println("</HEAD>");
out.println("<B0DY BGCOLOR='white'>");
out.printIn("<B>Hello, " + name + "</B>");
out.printIn("</BODY>");
out.println("</HTML>");
out. close () ;
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Hello JSP Code
<%! private static final String DEFAULT_NAME = "World"; %> <HTML>
<HEAD>
<TITLE>Hello JavaServer Page</TITLE>
</HEAD>
<%-- Determine the specified name (or use default) --%>
<%
String name = request.getParameter("name");
if ( (name == null) || (name.length() ==0) )
{
name = DEFAULT NAME;
}
%>
<BODY BGCOLOR='white'>
<B>Hello, <%= name %></B>
</BODY>
</HTML>
Think Possibility
JSP Scripting Elements
• JSP scripting elements are embedded with the <% %>
tags and are processed by the JSP engine during
translation of the JSP page.
<HTML>
<%-- scripting element --%>
</HTML>
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JSP Scripting Elements
There are five types of scripting elements:
1.
2.
3.
4.
5.
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Comments
Directive tag
Declaration tag
Scriptlet tag
Expression tag
<%-- comment --%>
<%@ directive %>
<%!
dec! %>
<%
code %>
<%= expr' %>
Comments
• Documentation is important to any application. There
are three types of comments permitted in a JSP page:
– HTML comments
<!-- This is an HTML comment. It will show up in the
response. -->
– JSP page comments
<%-- This is a JSP comment. It will only be seen in
the JSP code. It will not show up in either the
servlet code or the response. --%>
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Comments
• Java comments can be embedded with scriptlet and
declaration tags.
/* This is a Java comment. It will show up in the servlet
code. It will not show up in the response. */
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Directive Tag
• A directive tag provides information that will affect the
overall translation of the JSP page.
• The syntax for a directive tag is:
<%@ DirectiveName [attr="value"]* %>
• Examples:
<%@ page session="false" %>
<%@ include file="incl/copyright.html" %>
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The page Directive
• The page directive is used to modify the overall
translation of the JSP page.
<%@ page import="java.util.Date" %>
• Note:
You can have more than one page directive, but can
only declare any given attribute once per page, except
for the import attribute. You can place a page directive
anywhere in the JSP file. It is good practice to make
the page directive the first statement in the JSP file.
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The page Directive
• The page directive defines a number of pagedependent properties and communicates these to the
Web container during translation time.
– The language attribute defines the scripting
language to be used in the page.
– The extends attribute defines the (fully-qualified)
class name of the
superclass of the servlet class that is generated from
this JSP page.
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The page Directive
• The import attribute defines the set of classes and
packages that must be imported in the servlet class
definition.
• For example:
import="java.sql.Date,java.util.*,j ava.text.*"
• The session attribute defines whether the JSP page is
participating in an HTTP session. The value is either
true (the default) or false.
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The page Directive
•
•
•
The buffer attribute defines the size of the buffer
used in the outputstream (a JspWriter object). The
value is either none or Nkb.
For example:
buffer="8kb" or buffer="none“
The autoFlush attribute defines whether the buffer
output should be flushed automatically when the
buffer is filled or whether an
exception is thrown. The value is either true
(automatically flush) or false (throw an exception).
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The page Directive
• The isThreadSafe attribute allows the JSP page developer to
declare that the JSP page is thread-safe or not. If the value
is set to false, then this attribute instructs JSP parser to
write the servlet code such that only one HTTP request will
be processed at a time. The default value is true.
• The info attribute defines an informational string about the
JSP page.
• The errorPage attribute indicates another JSP page that will
handle all runtime exceptions thrown by this JSP page. The
value is a URL that is either relative to the current Web
hierarchy or relative to the context root.
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The page Directive
• The isErrorPage attribute defines that the JSP page has
been designed to be the target of another JSP page's
errorPage attribute. The value is either true or false
(default). All JSP pages that "are an error page"
automatically have access to the exception implicit
variable.
• The content Type attribute defines the MIME type of
the output stream. The default is text/html.
• The pageEncoding attribute defines the character
encoding of the output stream. The default is BO-88591. Other character encodings permit the inclusion of
non-Latin character sets, such as Kanji or Cyrillic.
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Declaration Tag
• A declaration tag allows you to include members in the
JSP servlet class, either attributes or methods. The
syntax for a declaration tag is:
<%! JavaClassDeclaration %>
• Examples:
<%! public static final String DEFAULT_NAME = "World";
%>
<%! public String getName(HttpServletRequest request)
{ return request.getParameter("name");}
<%! int counter = 0; %>
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Declaration Tag
• You can use a declaration tag to override the jsplnit
and jspDestory life cycle methods. The signature of
these methods has no arguments and returns void. For
example:
<%!
public void jsplnit() {
/* initialization code here */
public void jspDestroyO {
/* clean up code here */
%>
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Scriplet Tag
• A scriptlet tag allows the JSP page developer to include
arbitrary Java technology code in the _j spService
method. The syntax for a declarations tag is:
<% JavaCode %>
• Examples:
<% int i = 0; %>
<% if ( i > 10 ) { %>
I is a big number.
<% } else { %>
I is a small number
<% } %>
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Scriplet Tag
<TABLE BORDERS=‘1’ CELLSPACING='0' CELLPADDING='5'>
<TR><TH>number</TH>
<TH>squared</TH>
</TR>
<% for ( int i=0; i<10; i++ ) { %>
<TR><TD><%= i %></TD>
<TD><%= (i * i) %></TD>
</TR>
<% } %>
</TABLE>
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Expression Tag
• An expression tag holds a Java language expression that
is evaluated during an HTTP request. The result of the
expression is included in the HTTP response stream.
The syntax for a declaration tag is:
<%= JavaExpression %>
• Examples:
– <B>Ten is <%= (2*5) %></B>
– Thank you, <I><%= name %></l>, for registering for the
soccer league.
– The current day and time is: <%= new java.util.Date() %>
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Implicit Variables
• The Web container gives the JSP technology developer
access to the following variables in scriptlet and
expression tags. These variables represent commonly
used objects for servlets that JSP developers might
need to use.
Variable name
Description
request
The HttpServletRequest object associated with the request.
response
The HttpServletResponse object associated with the response
that is sent back to the browser.
out
The JspWriter object associated with the output stream of tl
response.
session
The HttpSession object associated with the session for the
given user of the request. This variable is only meaningful
if the JSP page is participating in an HTTP session.
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Implicit Variables
Variable name
Description
application
The ServletContext object for the Web application.
config
The ServletConf ig object associated with the servlet for
th JSP page.
pageContext
This object encapsulates the environment of a single
request for this JSP page.
page
This variable is equivalent to the this variable in the Java
programming language.
exception
The Throwable object that was thrown by some other JSP
page. This variable is only available in a "JSP error
page."
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JSP Page Exception
Handling
• The JSP specification provides a different
mechanism for handling exceptions.
• The page directive allows you to specify
another JSP page to be activated
whenever the JSP page throws an
exception.
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Declaring an Error Page
• The errorPage attribute of the page
directive is used to declare the error page
to be used by the Web container when this
JSP page throws an exception.
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Developing an Error Page
• The errorPage attribute of the page
directive is used to declare that this JSP
page has access to the exception implicit
variables. This is used by the Web
container when another JSP page throws
an exception.
Think Possibility
