JSP implicit objects

JSP implicit objects are created by container while translating JSP page to Servlet source to help developers. We can use these objects directly in scriptlets that goes in service method, however we can’t use them in JSP Declaration because that code will go at class level.

We have 9 implicit objects that we can directly use in JSP page. Seven of them are declared as local variable at the start of _jspService() method whereas two of them are part of _jspService() method argument that we can use.

1. out Object
2. request Object
3. response Object
4. config Object
5. application Object
6. session Object
7. pageContext Object
8. page Object
9. exception Object

1. out Object

   JSP out implicit object is instance of javax.servlet.jsp.JspWriter implementation and it’s used to output content to be sent in client response. This is one of the most used JSP implicit object and thats why we have JSP Expression to easily invoke out.print() method.

2. request Object

   JSP request implicit object is instance of javax.servlet.http.HttpServletRequest implementation and it’s one of the argument of JSP service method. We can use request object to get the request parameters, cookies, request attributes, session, header information and other details about client request.

3. response Object

   JSP response implicit object is instance of javax.servlet.http.HttpServletResponse implementation and comes as argument of service method. We can response object to set content type, character encoding, header information in response, adding cookies to response and redirecting the request to other resource.

4. config Object

   JSP config implicit object is instance of javax.servlet.ServletConfig implementation and used to get the JSP init params configured in deployment descriptor.

5. application Object

   JSP application implicit object is instance of javax.servlet.ServletContext implementation and it’s used to get the context information and attributes in JSP. We can use it to get the RequestDispatcher object in JSP to forward the request to another resource or to include the response from another resource in the JSP.

6. session Object

   JSP session implicit object is instance of javax.servlet.http.HttpSession implementation. Whenever we request a JSP page, container automatically creates a session for the JSP in the service method.
   Since session management is heavy process, so if we don’t want session to be created for JSP, we can use page directive to not create the session for JSP using <%@ page session="false" %>. This is very helpful when our login page or the index page is a JSP page and we don’t need any user session there.

7. pageContext Object

   JSP pageContext implicit object is instance of javax.servlet.jsp.PageContext abstract classimplementation. We can use pageContext to get and set attributes with different scopes and to forward request to other resources. pageContext object also hold reference to other implicit object.

8. page Object

   JSP page implicit object is instance of java.lang.Object class and represents the current JSP page. page object provide reference to the generated servlet class. This object is very rarely used.

9. exception Object

   JSP exception implicit object is instance of java.lang.Throwable class and used to provide exception details in JSP error pages. We can’t use this object in normal JSP pages and it’s available only in JSP error pages.

For Example Refer my next post