18. HttpSession in servlet


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HttpSession in servlet 

HttpSession:

HttpSession is an interface that provides a way to identify a user in multiple page requests. A unique session id is given to the user when first request comes. This id is stored in a request parameter or in a cookie.

How to get session object?

HttpServletRequest interface’s getSession() method is used to get the session object.
Syntax: HttpSession session = request.getSession();  

How to set attribute in session object?

HttpSession interface’s setAttribute() method is used to set attribute in session object.
Syntax: public void setAttribute(String name,Object value);
Example: session.setAttribute(“attName”, “attValue”); 

How to get attribute from session object?

HttpSession interface’s getAttribute() method is used to get attribute from session object.
Syntax: public Object getAttribute(String name);
Example: String value = (String) session.getAttribute(“attName”); 

Session management example using HttpSession:

LoginServlet.java
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
/**
* This class is used to set values in session.
* @author java tutorial point
*/
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
 
   //no-argument constructor
    public LoginServlet() {
 
    }
 
    protected void doPost(HttpServletRequest request, 
        HttpServletResponse response)
                   throws ServletException, IOException {
 response.setContentType("text/html"); 
     PrintWriter out = response.getWriter();
 
     //get parameters from request object.
     String userName = request.getParameter("userName").trim();
     String password = request.getParameter("password").trim();
 
     //check for null and empty values.
     if(userName == null || userName.equals("") || 
       password == null || password.equals("")){
      out.print("Please enter both username " +
        "and password. 

");
      RequestDispatcher requestDispatcher = 
       request.getRequestDispatcher("/login.html");
      requestDispatcher.include(request, response);
     }//Check for valid username and password.
     else if(userName.equals("jai") && password.equals("1234")){
      HttpSession session=request.getSession();  
                session.setAttribute("userName",userName);  
                session.setAttribute("password",password);
      out.println("Logged in successfully.
"); 
      out.println("Click on the below link to see " +
       "the values of Username and Password.
");
      out.println("" +
        "Click here
"); out.close(); }else{ out.print("Wrong username or password.

"
); RequestDispatcher requestDispatcher = request.getRequestDispatcher("/login.html"); requestDispatcher.include(request, response); } } }
DisplaySessionValueServlet.java
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
/**
* This class is used to get values from session.
* @author java tutorial point
*/
public class DisplaySessionValueServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
 
    //no-argument constructor
    public DisplaySessionValueServlet() {
 
    }
 
    protected void doGet(HttpServletRequest request, 
     HttpServletResponse response)
              throws ServletException, IOException {
 response.setContentType("text/html"); 
     PrintWriter out = response.getWriter();
 
     //get parameters from session object.
     HttpSession session=request.getSession(false);  
        String userName =(String)session.getAttribute("userName");  
        String password =(String)session.getAttribute("password");  
 
     out.println("Username: " + userName + "

");
     out.println("Password: " + password);
 
     out.close();
    }
}
login.html
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 
Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Login</title>
</head>
<body>
 <form action="LoginServlet" method="post">
  Username:<input type="text" name="userName"/>
  <br/><br/>
  Password:<input type="password" name="password"/>
  <br/><br/> 
  <input type="submit" value="login"/> 
 </form>  
</body>
</html>
web.xml
xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4" 
xmlns="http://java.sun.com/xml/ns/j2ee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 
  <servlet>
    <servlet-name>LoginServlet</servlet-name>
    <servlet-class>
     com.javawithease.business.LoginServlet
    </servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>LoginServlet</servlet-name>
    <url-pattern>/LoginServlet</url-pattern>
  </servlet-mapping>
 
  <servlet>
    <servlet-name>DisplaySessionValueServlet</servlet-name>
    <servlet-class>
     com.javawithease.business.DisplaySessionValueServlet
    </servlet-class>
  </servlet>
 
  <servlet-mapping>
    <servlet-name>DisplaySessionValueServlet</servlet-name>
    <url-pattern>/DisplaySessionValueServlet</url-pattern>
  </servlet-mapping>
 
  <welcome-file-list>
    <welcome-file>login.html</welcome-file>
  </welcome-file-list>
 
</web-app>

Session management example using HttpSession:


 
Enter username: jai and password: 1234


 
Click on login button.


 
Click on the link.
 


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