Java Practical info : JSP Implicit Object's

JSP Implicit Object's

<div dir="ltr" style="text-align: left;" trbidi="on">
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif";"><br /></span>
<div class="separator" style="clear: both; text-align: center;">
<span style="font-family: "Georgia","serif";"><iframe allowfullscreen="allowfullscreen" frameborder="0" height="266" mozallowfullscreen="mozallowfullscreen" src="https://www.youtube.com/embed/1YkQjDQIrqg?feature=player_embedded" webkitallowfullscreen="webkitallowfullscreen" width="320"></iframe></span></div>
<div style="text-align: center;">
<span style="font-family: "Georgia","serif";"><span style="line-height: 18.18181800842285px;"><br /></span></span></div>
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">During the translation phase, the jsp engine declares and
initializes nine commonly used variables in the service method of the generated
servlet. They are implicitly made available to a jsp without need of declaring
them. These are known as implicit variables or implicit objects. They are as
follows.<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoListParagraphCxSpFirst" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Request<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpMiddle" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Response<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpMiddle" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Session<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpMiddle" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Config<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpMiddle" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Application<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpMiddle" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Page<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpMiddle" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Exception<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpMiddle" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Out<o:p></o:p></span></div>
<div class="MsoListParagraphCxSpLast" style="margin-left: 1.0in; mso-add-space: auto; mso-list: l0 level2 lfo1; text-indent: -.25in;">
<span style="font-family: "Courier New"; font-size: 12.0pt; line-height: 115%; mso-fareast-font-family: "Courier New";">o<span style="font-family: 'Times New Roman'; font-size: 7pt; line-height: normal;">  
</span></span><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">pageContext<o:p></o:p></span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Request:-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> This
object is of type javax.Servlet.http.HttpServletREquest. It refers to the
current request to the jsp. By using this object we can capture the client
data. For example in a scriptlet we can write as follows.<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><%<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">            String
name=request.getParameter(“html textbox name”);<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">%><o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">With the above scriptlet we can get the form data directly
into the jsp.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Response</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">:- This
objet is of type javax.servlet.http.HttpServletResponse. It  is used for sending customized response to
the client.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Session:-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> This
object is of type javax.servlet.http.HttpSession. This object is not available
in a jsp if we  say <%@ page session=”false”
%>. In a servlet when we available in a jsp it is imlicitly available. If we
want to implement session tracking in a jsp, we make use of this object.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Config:-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> The
object is of type javax.servlet.ServletConfig. When initialization parameters
are supplied to the jsp explicitly from the web.xml. we can retrieve them by
using this object.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><% String paramvalue=config.getInitParameter(“Paramname”);
%><o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Application:-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> This
is an object of type javax.servlet.ServletContext. It refers to the environment
to which the jsp belongs. Using this object we can retrieve application level
state. All the web components(Jsps & servlets) running in the same
application can share common information. For example if a servlet or another
jsp has stored some info in the ServletContext object, in our current jsp we
can retrieve it as follows.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><%  String
value=(String)application.getAttribute(“name”); %><o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Page:-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> The is
an object of type java.lang.object. It refers to the instance of the generated
servlet. This is very rarely used in a jsp.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Exception:-</span></b><span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> This
object <o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<br /></div>

JSP Implicit Object's

During the translation phase, the jsp engine declares and initializes nine commonly used variables in the service method of the gener...

JSP Page Directives

<div dir="ltr" style="text-align: left;" trbidi="on">
<div class="separator" style="clear: both; text-align: center;">
<iframe allowfullscreen="allowfullscreen" frameborder="0" height="266" mozallowfullscreen="mozallowfullscreen" src="https://www.youtube.com/embed/e4n9ZBjYU1E?feature=player_embedded" webkitallowfullscreen="webkitallowfullscreen" width="320"></iframe></div>
<br />
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">While expressions, scriptlets and declarations are used to
define the logic to be executed at run-time(request processing time),
directives are used to provide pages with information at translation time –
when the jsp page is converted to a servlet.<o:p></o:p></span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Directives are used to specify the classes that are
imported, to specify the error page used for catching exceptions, to import tag
libraries and making them available to use on the page etc.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">JSP directives provide general information about the jsp
page to the JSP engine.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">JSP directives do not generate code. They are not part of
the logic within the JSP code. JSP directives provide directions and
instructions to the container, telling it how to handle certain aspects of JSP
specification. </span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">There are 3 types of directives according to jsp specification.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
</div>
<ul style="text-align: left;">
<li><span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">            Include
directive</span></li>
<li><span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">            Taglib
directive</span></li>
<li><span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">            Page
directive</span></li>
</ul>
<br />
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">A JSP directive is of the form<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><%@ directive attribute=value %><o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><b>Include Directive:-</b> An include directive telis the JSP
engine to include the contents of another file inline (exactly at the location
of directive usage) in the current jsp. Include file can be another jsp or a
HTML file. Include directive is of the following form </span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><%@ include file = “filename”
%><o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">The following example include the souce code of the
header.jsp in the current.jsp<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><a href="mailto:%25@include%20file%20=%20%E2%80%9Cheader.jsp%E2%80%9D%25">%@include
file = “header.jsp”%</a><o:p></o:p></span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">When the current jsp(the jsp in which this directive is
used) receives the client request, the jsp enine reads the entire jsp before
translation. Once include directive is encountered, the jsp engine copies the
contents of the header.jsp into the current jsp inline. Then it translates the
current jsp into a servlet. As this happens during the translation phase of the
jsp, we say that directives are translation time instructions that are given to
the jsp container(engine).<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Taglib directive:- This directive is used to tel the
container which tg library a specific JSP requires. It is also used to assign a
prefix gthat is used within the JSP page to identify tags from a specific tag
library. Now jsp engine can locate the code for these tag libraries and get
them ready for use by the JSP page. Taglib directive is of the form</span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"> <%@
taglib prefix=”name” url=”values”%>(More on this in custom tags).<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><b>Page Directive:</b>- This directive informs the engine about the
overall properties of a jsp page. This directive applies to the entire
translation unit and not just to the page in which it is declared. This
directive is of the following form.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><<a href="mailto:%25@page%20attribute=%E2%80%9Dvalue%E2%80%9D%20attribute=%E2%80%9Dvalue%E2%80%9D.....%25">%@page
attribute=”value” attribute=”value”.....%</a>><o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Even though there are many attributes for the page
directive, the most frequently used ones are discussed here.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><b>Import:-</b> This attribute is similar to the import statement
in a normal java source code. Once this attribute is used , the jsp container
inserts an import statement into the generated servlet for each of the packages
declared using this attribute. We can import multiple packages in a single tag by
using a comma-separated list of package names. We can also use multiple tags
for readability.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;">Ex:- <%@ page import=”java.io.*”%><o:p></o:p></span></div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><b>Session:- </b> This
attribute indicates to the jsp engine whether the current jsp takes part in a
http session. The default value is true. If we don’t want the jsp to
participate ina session, then we have to explicitly say<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><%@page session = “false” %><o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><b>errorPage:</b>- we can handle the exceptions in a jsp by writing
try and catch blocks. However, the jsp specification provides cleaner approach.
This approach separates the error hadling code from the main code from the main
page and thus promotes resability of exception handling mechanism. In this
approach, a jsp uses the error page attribute of the page directive to delegate
the exception to another JSP page that has the error handling code.<o:p></o:p></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><<a href="mailto:%25@page%20errorPage=%E2%80%9Dhandler.jsp%E2%80%9D%25">%@page
errorPage=”handler.jsp”%</a>><o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal" style="text-align: justify;">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><b>isErrorpage:-</b> This attribute conveys whether the current jsp
can act as an error handler for any other jsp. By default this value is false.
In the abouve example, when we write handler.jsp. In that file we must use the
following statement.<o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><%@page isErrorPage=”true”><o:p></o:p></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><b>Content Type:-</b> This attribute specifies the MIME type of the
output. The default values is text/html. </span><span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;">If we want to change the MIME type we can say as follows.</span></div>
<div class="MsoNormal">
<span style="font-family: Georgia, serif; font-size: 12pt; line-height: 115%;"><br /></span></div>
<div class="MsoNormal">
<span style="font-family: "Georgia","serif"; font-size: 12.0pt; line-height: 115%;"><%@page contentType=”image/gif” %><o:p></o:p></span></div>
<div class="MsoNormal">
<br /></div>
</div>

JSP Page Directives

While expressions, scriptlets and declarations are used to define the logic to be executed at run-time(request processing time), direct...