Implicit objects advance Java

Implicit Objects
Advance Java
(2160707)
Prepared By::
Metaliya Darshit (130110107020)

INTRODUCTION
JSP Implicit Objects are the Java objects that the JSP Container
makes available to developers in each page and developer can
call them directly without being explicitly declared.
JSP Implicit Objects are also called pre-defined variables.

Object Description
Request This is the HttpServletRequest object associated with the request.
response
This is the HttpServletResponse object associated with the response to the
client.
out This is the PrintWriter object used to send output to the client.
session This is the HttpSession object associated with the request.
application This is the ServletContext object associated with application context.
config This is the ServletConfig object associated with the page.
pageContext
This encapsulates use of server-specific features like higher performance
JspWriters.
page
This is simply a synonym for this, and is used to call the methods defined
by the translated servlet class.
Exception
The Exception object allows the exception data to be accessed by
designated JSP.

REQUEST OBJECT
Implicit object of type HttpServletRequest i.e. created for each
jsp request by the web container.
Use:
To get request information such as parameter, header
information, remote address, server name, server port,
content type, character encoding
To set, get and remove attributes from the jsp request
scope.

REQUEST OBJECT
Index.html
<form action="welcome.jsp">
<input type="text" name="uname">
<input type="submit" value="go"><br/>
</form>
Newjsp.jsp
<%
String name=request.getParameter("uname");
out.print("welcome "+name);
%>

RESPONSE OBJECT
Implicit object of type HttpServletResponse. The instance of
HttpServletResponse is created by the web container for each
jsp request.
Defines the interfaces that deal with creating new HTTP
headers. Through this object the JSP programmer can add new
cookies or date stamps, HTTP status codes etc.
Use:
To add or manipulate response such as redirect response
to another resource, send error etc.
Newjsp.jsp
<%
response.sendRedirect("http://www.google.com");

OUT OBJECT
Instance of a javax.servlet.jsp.JspWriter object and is used to
send content in a response.
Use:
For writing any data to the buffer
displaying dynamic data
The java way to display text on the webpage
Newjsp.jsp
<% out.print("Today is:"+java.util.Calendar.getInstance().getTime());
%>

SESSION OBJECT
implicit object of type HttpSession.
Use:
to set, get or remove attribute or to get session
information.
to track client session between client requests

SESSION OBJECT
Index.html
<form action="welcome.jsp">
<input type="text" name="uname">
<input type="submit" value="go"><br/>
</form>
Newjsp.jsp
<%
out.print("Welcome "+name);
session.setAttribute("user",name);
%><a href="second.jsp">second jsp page</a>

SESSION OBJECT
second.jsp
<%
String name=(String)session.getAttribute("user");
out.print("Hello "+name);
%>

APPLICATION OBJECT
Implicit object of type ServletContext.
Instance of ServletContext is created only once by the web
container when application or project is deployed on the server.
Use
To get initialization parameter from configuaration file
(web.xml).
To get, set or remove attribute from the application scope.

APPLICATION OBJECT
Newjsp.jsp
<%
out.print("Welcome "+request.getParameter("uname"));
String driver=application.getInitParameter("dname");
out.print("driver name is="+driver);
%>

CONFIG OBJECT
Implicit object of type ServletConfig.
Use:
To get initialization parameter for a particular JSP page
Allows the JSP programmer access to the Servlet or JSP
engine initialization parameters such as the paths or file
locations etc.

PAGECONTEXT OBJECT
Implicit object of type PageContext class
Intended as a means to access information about the page
while avoiding most of the implementation details.
Use:
To set, get or remove attribute from one of the following
scopes:
page
request
session
Application
In JSP, page scope is the default scope.

PAGECONTEXT OBJECT
Newjsp.jsp
<%
out.print("Welcome "+name);
pageContext.setAttribute("user",name,PageContext.SESSION_SC
OPE); %>
<a href="second.jsp">second jsp page</a>

PAGECONTEXT OBJECT
second.jsp
<%
String name=(String)pageContext.getAttribute("user",PageContext.SES
SION_SCOPE);
out.print("Hello "+name);
%>

PAGE OBJECT
An actual reference to the instance of the page.
It can be thought of as an object that represents the entire JSP
page.
implicit object of type java.lang.Throwable class.
The exception object is a wrapper containing the exception
thrown from the previous page. It is typically used to generate
an appropriate response to the error condition.

EXCEPTION OBJECT
implicit object of type java.lang.Throwable class.
A wrapper containing the exception thrown from the previous
page.
Use:
To generate an appropriate response to the error
condition.

Implicit objects advance Java

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