e-PG Pathshala
Subject: Computer Science Paper: Web Technology
Module: SERVLET SESSION and SERVLET WITH JDBC Module No: CS/WT/32
Quadrant 2 – e-text
Learning Objectives
The last module has explained about the need for Session Management and discussed about the different approaches of Session Management. The previous module has discussed about the different methods to maintain sessions such as using cookies, hidden form fields and URL Rewriting.
This module will enable us to learn about Session Tracking in Java by using HttpSession API . This module will also explain about how Servlets can communicate with databases via JDBC (Java Database Connectivity) and will illustrate it with an example.
Session Management API
Session Management API is built by utilizing the different concepts used in the different approaches we have already explained for session tracking. There were disadvantages that exists in the previous approaches and all the previous methods are not complete by themselves. Hence it is required to provide a solution that can utilize these concepts of session tracking to provide session management in all cases.
Java provides Session Management API and J2EE Servlet technology that we can use to
maintain sessions.
Session Management
When a Http client interacts with the web server, a session id is created and for subsequent requests by the client the same session id is used to recognize the client by the server. This session is maintained until the client disconnects from the server or closes his browser.
This is shown diagrammatically for two clients interacting with the server with its own session id in Figure 32.1.
Figure 32.1 Session Management
Session Tracking in Java
Servlets include a built-in Session API. A server complying with the Java servlet API supports
the session concept by associating an HttpSession object with each session maintained by the
server. HttpSession object is created by the server when a servlet call the getSession() method
on its HttpServletRequest parameter.
The following syntax is used to create HttpSession object.
HttpSession session = request.getSession();
Using the Session API
Steps to use the Java Session API:
1) Get the Session object from the HTTPSession object.
2) Extract Data from the user’s Session Object
3) Extract information about the session object” e.g. when was the session created, session ID etc.
4) Add data to the user’s Session Object.
Session Tracking Basics
The basic steps we follow to work with session tracking is given below.
•
Access the session object.
Use the method request.getSession to get HttpSession object.
HttpSession session = request.getSession();
•
Look up information (user data) associated with a session.
Use the method getAttribute on the HttpSession object to get information associated with the session.
•
Store information in a session.
Use the method setAttribute with a key and a value to add data to the user's session
object.
•
Discard session data.
Use the method
removeAttributethat discards a specific value associated with a specified “key” (This is the most common approach used).
We can call
invalidateto discard an entire session and all user data will be lost including the data created by other Servlets or JSP pages.
HttpSession Object Methods
Some of the useful methods to work with HttpSession object is given in Table 32.1.
Table 32.1 HttpSession Object Methods
Methods Description
long getCreationTime()
returns the time when the session was created, measured in milliseconds since midnight January 1, 1970 GMT.
String getId() returns a string containing the unique
identifier assigned to the session.
long getLastAccessedTime() returns the last time the client sent a request associated with the session
int getMaxInactiveInterval() returns the maximum time interval, in seconds.
void invalidate() destroy the session
boolean isNew() returns true if the session is new else false void setMaxInactiveInterval(int interval) Specifies the time, in seconds, after servlet
container will invalidate the session.
Example: DateServlet
This Servlet program is to demonstrate about maintaining session which displays the last accessed date and the current date of the session whenever the Servlet is invoked.
The first step is to create a new session object using the
getSession()method of
HttpServletRequestobject to associate a session with the Servlet. Initially no date is associated with the session hence when the first time the Servlet is invoked, it displays the current date/time. This date object created is set with the session using the method
setAttribute()of the
HttpSessionobject. When the next time the Servlet is called, it retrieves the date from the session object using the method
getAttribute()and displays the last accessed date and the current date.
import java.io.*;
importjava.util.*;
importjavax.servlet.*;
importjavax.servlet.http.*;
public class DateServlet extends HttpServlet {
protected void processRequest(HttpServletRequest request,
HttpServletResponse response) throwsServletException, IOException {
HttpSession hs= request.getSession(true);
response.setContentType("text/html;charset=UTF-8");
try (PrintWriter out = response.getWriter()) {
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet AddCookieServlet</title>");
out.println("</head>");
out.println("<body><center>");
out.print("<B>");
//Display date/time of last access.
Date date=(Date)hs.getAttribute("date");
if(date!=null) {
out.print("Last access: "+ date +"<br>");
}
//Display current date/time.
date=new Date();
hs.setAttribute("date",date);
out.println("Current date: "+date);
out.println("</center></body>");
out.println("</html>");
} }
protected void doGet(HttpServletRequest request, HttpServletResponse response) throwsServletException, IOException
{
processRequest(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)mthrowsServletException, IOException
{
processRequest(request, response);
}
public String getServletInfo() { return "Short description";
} }
Web.xml
We need to compile the above servlet, DateServlet and create appropriate entry in web.xml file.
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1">
<session-config>
<session-timeout>
30
</session-timeout>
</session-config>
<servlet>
<servlet-name>HttpSess</servlet-name>
<servlet-class>DateServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HttpSess</servlet-name>
<url-pattern>/DateServlet</url-pattern>
</servlet-mapping>
</web-app>
DateServlet Output
Figure 32.2 shows the output of the DateServlet when the servlet is invoked initially.
Figure 32.2 Output of DateServlet
After sending another request Output
The output of the DateServlet when the servlet is invoked subsequently shown in Figure 32.3.
Figure 32.3 Output of DateServlet
Session Tracking Example
The following Servlet demonstrates the use of session, by counting the number of accesses within this session from a particular client. The example illustrates the use of methods like
getID()to retrieve the session ID,
getCreationTime()and
getLastAccessedTime()to get the session creation and last accessed times.
The first step is to create a new session object using the
getSession()method
of
HttpServletRequest.
Then we get the session ID using the method
getID(), session creation time using the method
getCreationTime()and the last access time of this web page using the method
getLastAccessedTime().The program then checks if a session is new then it stores the title to be displayed as
"Welcome to my website"
and set the userID to the session. When the next time the servlet is invoked, it displays the title as
" Welcome Back to my website"and sets the visit count to the session object. Every time the page is accessed the visit count is incremented and is set to the session, retrieved and displayed.
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
// Extend HttpServlet class
public class SessionTrack extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
// Create a session object if it is already not created.
HttpSession session = request.getSession(true);
// Get session creation time.
Date createTime = new Date(session.getCreationTime());
// Get last access time of this web page.
Date lastAccessTime = new Date(session.getLastAccessedTime());
String title = "Welcome Back to my website";
Integer visitCount = new Integer(0);
String visitCountKey = new String("visitCount");
String userIDKey = new String("userID");
String userID = new String("ABCD");
// Check if this is new comer on your web page.
if (session.isNew()) {
title = "Welcome to my website";
session.setAttribute(userIDKey, userID);}
else {
visitCount = (Integer)session.getAttribute(visitCountKey);
visitCount = visitCount + 1;
userID = (String)session.getAttribute(userIDKey);
}
session.setAttribute(visitCountKey, visitCount);
// Set response content type
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String docType = "<!doctype html public \"-//w3c//dtd html 4.0 " +
"transitional//en\">\n";
out.println(docType + "<html>\n" + "<head><title>" + title +
"</title></head>\n" +
"<body bgcolor=\"#f0f0f0\">\n" +
"<h1 align=\"center\">" + title + "</h1>\n" +
"<h2 align=\"center\">Session Information</h2>\n" +
"<table border=\"1\" align=\"center\">\n" +
"<tr bgcolor=\"#949494\">\n" +
" <th>Session info</th><th>value</th></tr>\n" +
"<tr>\n" +
" <td>id</td>\n" + " <td>" + session.getId() + "</td>
</tr>\n" +
"<tr>\n" +
" <td>Creation Time</td>\n" + " <td>" + createTime +
" </td></tr>\n" +
"<tr>\n" +
" <td>Time of Last Access</td>\n" + " <td>" + lastAccessTime +
" </td></tr>\n" +
"<tr>\n" +
" <td>User ID</td>\n" + " <td>" + userID + " </td>
</tr>\n" +
"<tr>\n" +
" <td>Number of visits</td>\n" + " <td>" + visitCount +
"</td>
</tr>\n" +
"</table>\n" +
"</body></html>"); } }
Output
Welcome to my website Session Information
Session info value
id 0AE3EC93FF44E3C525B4351B77ABB2D5 Creation Time Tue Jun 08 17:26:40 GMT+04:00 2010 Time of Last Access Tue Jun 08 17:26:40 GMT+04:00 2010
User ID ABCD
Number of visits 0
Servlet with JDBC
Servlets can communicate with databases via JDBC (Java Database Connectivity). JDBC provides a uniform way for a Java program to connect with a variety of databases in a general manner without having to deal with the specifics of those database systems.
Example
This example program demonstrates the design of an HTML form to get the Name and RollNo from the user whose value will be retrieved in a Servlet program and stored in the database.
<html>
<body>
<form method = "get"
action= "http:\\127.0.0.1:8080\servlet-html\Servlet_jdbc.html">
Name <input type=input name="Name" value="">
<br>
RollNo <input type=input name="RollNo" value="">
<br>
<input type=submit value="submit">
</form>
</body>
</html>
Example: Establishing JDBC connection
This example illustrate a simple Servlet JDBC program that gets the RollNo and Name from the
client and store it in a database.
Initially the Servlet retrieves the information from the HTML page using the
getParameter()method.
To establish JDBC connection, we need to dynamically load and register the driver. Then establish a connection by creating a Connection object using the DriverManager class. Then use the method
executeUpdate() to insert the retrieved values into the database. and executeQuery() to display the values from the database.import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class Servlet_jdbc extends HttpServlet {
public void doGet(HttpServletRequest req,HttpServletResponse res) throws ServletException ,IOException
{
res.setContentType("text/html");
PrintWriter out = res.getWriter();
String str1=req.getParameter("Name");
String str2=req.getParameter("RollNo");
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection con=DriverManager.getConnection("jdbc:odbc:test");
Statement st=con.createStatement();
String query="select * from student";
String q2 = "insert into student values ('" + str1 + "'," + str2 + ")";
st.executeUpdate(q2);
ResultSet rs=st.executeQuery(query);
while(rs.next()) {
out.println(rs.getString("Name")); //getString() out.println(rs.getInt("RollNo"));//getInt()
}
con.close();
}
catch(Exception e) {
}
out.println("Submission Successful");
}
Output: Servlet with JDBC
The output of this Servlet JDBC program is shown in Figure 32.4 and Figure 32.5.
Figure 32.4 HTML Page
Figure 32.5 Inserting into Database
Example: Servlet with JDBC
This is an another example to demonstrate about Servlet with JDBC. We design the HTML page in which the user inputs the information such as Database driver name, Database name, User name, Password and Query to execute.
When the servlet is invoked, the first step is to load and register the driver using database driver name. Then the connection is established using the database name, username and password. Then the servlet checks if the query string is a
"Select"query, and if so it executes the query using the method
executeQuery()that returns the
ResultSetobject. From the
ResultSetobject, it uses the method
getMetaData()to return a
ResultSetMetaDataobject.
Using this
ResultSetMetaDataobject we can get the column count using the method
getColumnCount(). Then use a for loop and retrieve the column name using the method
getColumnName() and the values stored in the column to display the records from the database. If the query string is not a "Select" query then the method
executeUpdate() is used to execute the query string which returns the number of rows affected by the query statement which is displayed to the user.
import java.io.*;
import java.sql.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class DemoServlet extends HttpServlet {
protected void processRequest(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
try (PrintWriter out = response.getWriter()) {
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet DemoServlet</title>");
out.println("</head>");
out.println("<body>");
String db_driver=request.getParameter("driv");
String db_name=request.getParameter("ur");
String db_uname=request.getParameter("uname");
String db_pwd=request.getParameter("pwd");
String db_query=request.getParameter("qry");
try {
Class.forName(db_driver);
Connection
connection=DriverManager.getConnection("jdbc:mysql://localhost:3306/
"+db_name,db_uname,db_pwd);
Statement stmt=connection.createStatement();
String q=db_query;
String first_word=q.split(" ")[0];
if(first_word.equals("Select")||first_word.equals("select")||first_word.equa ls("SELECT"))
{
ResultSet rs=stmt.executeQuery(q);
ResultSetMetaData rsmd=rs.getMetaData();
int columncount=rsmd.getColumnCount();
out.println("<TABLE BORDER=1 ALIGN='CENTER'>");
if(columncount>=1) {
out.println("<TR>");
for(int i=1;i<=columncount;i++) {
out.println("<TH>"+rsmd.getColumnName(i));
}
out.println();
while(rs.next()) {
out.println("<TR>");
for(int i=1;i<=columncount;i++) {
out.println("<TD>"+rs.getString(i));
}
out.println();
}
out.println("</TABLE>");
connection.close();
} else {
out.println("<h1>No Records found!</h1>");
connection.close();
}
} else {
int ers=stmt.executeUpdate(q);
if(ers>0) {
out.println("<h1>Statement Executed! "+ers+" rows affected</h1>");
} else {
out.println("<h1>Statement Executed and 0 rows affected!</h1>");
}
connection.close();
} }
catch(ClassNotFoundException cnfe) {
System.err.println("Error Loading Driver:"+cnfe);
}
catch(SQLException sqle) {
System.err.println("Error Connecting:"+sqle);
}
catch(Exception ex) {
System.err.println("Error with Input:"+ex);
}
out.println("</body>");
out.println("</html>");
} }
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { processRequest(request, response);
}
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException { processRequest(request, response);
} }
