Introduction
A Session is a period of a user's interaction with the server. Whenever a user
accesses any page of the server, then the server creates session for the user.
The server provides a unique id to each session called session id. The
session of the user remains active while the user keeps on interacting with the
server. If the user does not interact with the server for a period of 30 min
then the session gets destroyed. This period is called the default inactive
interval. The server can change the period for the default inactive interval. If the
user closes the browser then the session also gets destroyed. The server can
destroy the session of the user explicitly. A servlet can use the session of user to
create some variables. These variables occupy server memory. Users
cannot deny creation of session variables. One servlet can create session
variables and other servlets can fetch or change the value of session variables.
Creation and reading process of session
- Servlet must be a sub class of HttpServlet.
- Create the reference of
javax.servlet.http.httpsession by using getSession() method of
HttpservletRequest
- Use set attribute method of Httpsession to
create session variables. Use getAttribute() of Httpsession to find value of
session variables.
Method of HTTP session
1. Public void setAttribute(string variable name,object value)
This creates a variable within the user's session
2. Public object getAttribute(string variable name)
This returns the value of the specified session variable. If the specified variable
dose not exist in the user session then it returns null.
3. Public void invalidate();
It destroys all the variables present in the user's session
4. Public void setMaxInactiveInterval(long seconds)
It changes the default period of the Inactive interval.
Example
This servlet will accept a set of numbers one by one
infinitely and display the summation result below to the form after each
submission of the number
Summation.java file- import javax.servlet.*;
- import javax.servlet.http.*;
- import java.io.*;
-
- public class summation extends HttpServlet
- {
- public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException
- {
- PrintWriter out = res.getWriter();
- out.println("<html><body bgcolor='yellow'>");
- String s1 = req.getParameter("t1");
- out.println("<form >");
- out.println("<h1>Number<input type='text' name='t1'></h1>");
- out.println("<input type='submit' value='summation'>");
- out.println("</form>");
- int result = 0;
- HttpSession ses = req.getSession();
- Integer s2 = (Integer) ses.getAttribute("sum");
- if (s1 != null)
- {
- if (s2 == null)
- result = Integer.parseInt(s1);
- else
- result = Integer.parseInt(s1) + s2;
- ses.setAttribute("sum", result);
- out.println("<h1>Summation is :" + result + "</h1>");
- }
- out.println("</body></html>");
- }
- }
web.xml settings- <?xml version="1.0" encoding="ISO-8859-1"?>
- <!--
- Licensed to the Apache Software Foundation (ASF) under one or more
- contributor license agreements. See the NOTICE file distributed with
- this work for additional information regarding copyright ownership.
- The ASF licenses this file to You under the Apache License, Version 2.0
- (the "License"); you may not use this file except in compliance with
- the License. You may obtain a copy of the License at
- http://www.apache.org/licenses/LICENSE-2.0
- Unless required by applicable law or agreed to in writing, software
- distributed under the License is distributed on an "AS IS" BASIS,
- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- See the License for the specific language governing permissions and
- limitations under the License.
- -->
- <web-app xmlns="http://java.sun.com/xml/ns/javaee"
- xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
- xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
- version="2.5">
- <servlet>
- <servlet-name>summation</servlet-name>
- <servlet-class>summation</servlet-class>
- </servlet>
- <servlet-mapping>
- <servlet-name>summation</servlet-name>
- <url-pattern>/summation</url-pattern>
- </servlet-mapping>
- </web-app>
Compile
javac -cp servlet-api.jar summation.java (for tomcat 6.0)
Output
Run the tomcat then write the below line in the URL
Here the test is the Context path, which we mentioned in the server.xml file, which
is present in (E:\Program Files\Apache Software Foundation\Tomcat 6.0\conf)
directory.
http://localhost:8081/test/summation
Thanks for reading