How to Find Duplicate String in Java

Since we all known HashSet is a part of Collection that will store unique value always 
>  if we are trying to add any duplicate value add method return  false.
> add Method check existing Object Hashcode and compare with  newly added Object
if hashCode match then add method Return False else Return True .
>here we created HashSet<String> Object with generic type data type
>since we Added <String> After HashSet then it only allows to add String value
>generic type is only use to overcome data type casting problem 
..
Please Check below programmer 




/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package javainterview;
import java.util.*;

/**
 *
 * @author shiboo
 */
public class Duplicate {
    
    public static void main(String[] args) {
        
        String [] arr= {"Anand","Ajeet","Antrish","Anand"};
        HashSet<String>hset= new HashSet<String>();
        for(String value:arr){
        if(!hset.add(value)){
            System.out.println("Duplicate Value=>"+value);
        }
        }
        
    }
    
}

parse JSON in Java

How to parse json in java .? Add org.json lib into your project 


public class PraseJSON {
    public static void main(String[] args) throws JSONException {
       String json = "{\n"
                + "   \"Name\": {\n"
                + "         \"Place\": \"Bangalore\",\n"
                + "         \"Age\": \"23\"\n"
                + "    }}";
              
               // + "}";

        PraseJSON classObject = new PraseJSON();
        JSONObject obj = new JSONObject(json);
        String name = obj.getJSONObject("Name").getString("Place");
        System.out.println("Name::"+name);

}}

How to Create JSON in Java ?

we can easily create JSON in java Using org.json.simple library .so build this jar into your application .

• Create JSONObject  :

public class JSON{
 public static void main(String[] args) {

        JSONObject jsonObject = new JSONObject();
        jsonObject.put("Name", "Anand");
        jsonObject.put("Age", new Integer(23));
        jsonObject.put("Married",new Boolean(false));

     System.out.println(jsonObject); 
/*

{"Married":false,"Age":23,"Name":"Anand"}
*/

}

• Create JSONArray : 

 
public class JSON{
 public static void main(String[] args) {

        JSONObject jsonObject = new JSONObject();
        jsonObject.put("Name", "Anand");
        jsonObject.put("Age", new Integer(23));
        jsonObject.put("Married",new Boolean(false));
     JSONArray jsonarray = new JSONArray();
        jsonarray.add(jsonObject);//

     System.out.println(jsonarray); 
/*
 [{"Married":false,"Age":23,"Name":"Anand"}]
*/

}


 

Full String Class Method is Java

Here is the List of Methods than can be applicable With String class . please Check Below Programme
===============================================================
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package Com.interview;

import java.util.Locale;

/**
 *
 * @author anand
 */
public class StringFullMethod {
    
    public static void main(String[] args) {
        
        String s = "Anand";
        System.out.println(s.charAt(1));
        System.out.println(s.chars());
        System.out.println(s.codePointAt(1));
        System.out.println(s.codePointBefore(2));
        System.out.println(s.codePointCount(1, 3));
        System.out.println(s.codePoints());
        System.out.println(s.compareTo("Antrish"));
        System.out.println(s.compareToIgnoreCase("anand"));
        System.out.println(s.concat(" Dwivedi"));
        System.out.println(s.contains("An"));
        System.out.println(s.contentEquals("Anand"));
        System.out.println(s.contentEquals(new StringBuffer("Antrish")));
        System.out.println(s.endsWith("d"));
        System.out.println(s.equals(s));
        System.out.println(s.getBytes().length);
        System.out.println(s.getClass());
        System.out.println(s.hashCode());
        System.out.println(s.indexOf("A"));
        System.out.println(s.indexOf(1));
        System.out.println(s.indexOf("n", 2));
        System.out.println(s.intern());
        System.out.println(s.isEmpty());
        System.out.println(s.lastIndexOf("a"));
        System.out.println(s.lastIndexOf("n", 1));
        System.out.println(s.length());
        System.out.println(s.matches("Anand"));
        System.out.println(s.offsetByCodePoints(1, 2));
        System.out.println(s.replace("A", "a"));
        System.out.println(s.replaceAll("Anand", "Antrish"));
        System.out.println(s.replaceFirst("A", "n"));
        System.out.println(s.split("").length);
        System.out.println(s.toCharArray());
        System.out.println(s.toLowerCase());
        System.out.println(s.toLowerCase(Locale.GERMANY));
        System.out.println(s.toString());
        System.out.println(s.toUpperCase());
        System.out.println(s.toUpperCase(Locale.FRENCH));
        System.out.println(s.trim());
       
    }
}

O/P
n
java.util.stream.IntPipeline$Head@b4c966a
110
110
2
java.util.stream.IntPipeline$Head@4e50df2e
-19
0
Anand Dwivedi
true
true
false
true
true
5
class java.lang.String
63402602
0
-1
3
Anand
false
2
1
5
true
3
anand
Antrish
nnand
5
Anand
anand
anand
Anand
ANAND
ANAND
Anand

BUILD SUCCESSFUL (total time: 0 seconds)

Online Book Store Website Using Java

===============================================
Login.html:-
================================================
<html>
    <title>|| Login Page ||</title>
    <body class="bod">
        <form action='login.action'  method="post">
            <table align='center'>
                <tr><td colspan='2' align='center'>
                        <br></br>
                        <h2 style="color: black; font-size: 30px; padding-top: 1%;" class="Head">User Login</h2></td></tr>

                <tr>
                    <td><h2>UserName</h2></td>
                    <td><input type='text' name='UserName' placeholder="UserName" autocomplete="off" required=""/></td></tr>
                <tr>
                    <td><h2>password</h2></td>
                    <td><input type='password' name='Password' placeholder="password" autocomplete="off" required=""/></td></tr>
                <tr>
                    <td align="center" colspan=2><input type='submit' value='Submit' style="background-color: indianred" class="But"/></td></tr>
            </table>
            <div id="footerbottom">
                <div class="footerwrap">
                    <div id="copyright">2015 - Designed By -Anand Dwivedi.<a href="http://learnjavabyanand.blogspot.in/" target="_blank"><img src="test.png" width="150" height="28" border="0"  /></a></div>

                </div>
            </div>
        </form>
        <style type="text/css">

            .formd{
                background-color: darkcyan;
                text-align: center;
                alignment-adjust: center;
                margin-left: 42%;

            }
            .bod{
                background-color:darkcyan;
                text-align: center;
                margin-top: 13%;
            }
            .tb{
                alignment-adjust: center;
                alignment-baseline: central;
            }
            .But{
                margin-top: 9%;
            }
            .footerwrap{
                background-color: #7a7a7a;
                position:absolute;
                bottom:0;
                width:100%;
                left:  -0.5px;
                height:50px; 
                text-align: center;

            }
            .Head{
                background-color: #7a7a7a;
                position:absolute;
                top: -23px;
                width: 100%;
                left: -0.5;
                height: 50px;
                text-align: center;

            }

        </style>
    </body>
</html>
================================================
Session.html:-
================================================
<!DOCTYPE html>
<!--
To change this license header, choose License Headers in Project Properties.
To change this template file, choose Tools | Templates
and open the template in the editor.
-->
<html>
  
    <body>
        <form action="TestBook.action" method="post" >
        <input type="button" name="Click Here to Check Session" value="Click Here to Check Session"/>
    </form>
        </body>
   
</html>
================================================
Index.jsp
================================================
<%--
    Document   : newjspTest
    Created on : Aug 7, 2015, 3:15:17 PM
    Author     : ananddw
--%>


<html>
    <body class="bod">
        <title>|| Select Book || </title>
    <center>
        <h1 style="color: black; font-size: 30px; padding-top: 1%;" class="Head"> BookStore</h1>

        <form action="searchbook.action" method="post" class="formd" >
            <table class="tb">
                <tr>
                    <td style="alignment-adjust: center; text-align:center; color: darkgrey;"><h2>Select Category</h2>
                    </td>
                </tr>
                <tr>
                    <td><select name="category" style="background-color: mediumpurple">
                            <option value="Select">Select</option>
                            <option value="Java">Java</option>
                            <option value="Testing">Testing</option>
                            <option value=".NET">.NET</option>
                            <option value="SAP">SAP</option>
                        </select></td>
                </tr>
                <br></br>
                <tr>
                    <td><input type="submit" value="SearchBooks"  style="background-color: indianred" class="But">
                    </td>
                </tr>
            </table>


            <table class="tb" align="right">
                <tr>
                    <td>
                        <h1>
                            Total Visited :<%=application.getAttribute("TV")%>
                        </h1></td>
                </tr>
                <tr>
                    <td>
                        <h1>
                            Total Active :<%=application.getAttribute("TA")%>
                        </h1></td>
                </tr>
            </table>

            <a href="logout.action" class="logout">LOGOUT</a>






            <div id="footerbottom">
                <div class="footerwrap">
                    <div id="copyright">2015 - Designed By -Anand Dwivedi.<a href="http://learnjavabyanand.blogspot.in/" target="_blank"><img src="test.png" width="150" height="28" border="0"  /></a></div>

                </div>
            </div>
        </form>
        <style type="text/css">
            .formd{
                background-color: darkcyan;
                text-align: center;
                alignment-adjust: center;
                margin-left: 42%;

            }
            .bod{
                background-color:darkcyan;
                text-align: center;
                margin-top: 5%;
            }
            .tb{
                alignment-adjust: center;
                alignment-baseline: central;
            }
            .But{
                margin-top: 20%;
            }
            .footerwrap{
                background-color: #7a7a7a;
                position:absolute;
                bottom:0;
                width:100%;
                left:  -0.5px;
                height:50px; 
                text-align: center;

            }
            .Head{
                background-color: #7a7a7a;
                position:absolute;
                top: -23px;
                width: 100%;
                left: -0.5;
                height: 50px;
                text-align: center;
            }
            .logout{

                position:absolute;
                top: -23px;
                width: 10%;
                left: -0.5;
                height: 50px;
               text-decoration-color: aqua;
                margin-left: 88%;
            margin-top: 4%;
            }
        </style>
    </center>
</body>
</html>
================================================
logout.jsp
================================================
<%@ page session="false"%>
<html>
    <body class="bod">
        <table align="right" class="tb">
            <tr>
                <td>
                    <h3>
                        Total Visited :<%=application.getAttribute("TV")%>
                    </h3></td>
            </tr>
            <tr>
                <td>
                    <h3>
                        Total Active :<%=application.getAttribute("TA")%>
                    </h3></td>
            </tr>
        </table>
        <br />
        <br />
        <h2>You have logged out successfully</h2>
        <br />
        <br />
        <a href="Login.html">Go To Login Page</a>

        <div id="footerbottom">
            <div class="footerwrap">
                <div id="copyright">2015 - Designed By -Anand Dwivedi.<a href="http://learnjavabyanand.blogspot.in/" target="_blank"><img src="test.png" width="150" height="28" border="0"  /></a></div>

            </div>
        </div>
    </body>
    <style type="text/css">
        .formd{
            background-color: darkcyan;
            text-align: center;
            alignment-adjust: center;
            margin-left: 42%;

        }
        .bod{
            background-color:darkcyan;
            text-align: center;
            margin-top: 5%;
        }
        .tb{
            alignment-adjust: center;
            alignment-baseline: central;
        }

        .footerwrap{
            background-color: #7a7a7a;
            position:absolute;
            bottom:0;
            width:100%;
            left:  -0.5px;
            height:50px; 
            text-align: center;

        }
        .Head{
            background-color: #7a7a7a;
            position:absolute;
            top: -23px;
            width: 100%;
            left: -0.5;
            height: 50px;
            text-align: center;
        }

    </style>
</html>
==============================================
placeorder.jsp
==============================================
<%--
    Document   : newjspTest
    Created on : Aug 7, 2015, 3:50:05 PM
    Author     : ananddw
--%>

<%@ page import="java.util.*"%>
<html>
    <title>|| Place Order ||</title>
    <body  class="bod">
    <center>

        <h2 class="Head">Book Search</h2>
        <h1 class="Header">Your order has been Done !</h1>
        <%
            session.invalidate();
        %>
        <br /> <a href="index.jsp">GO TO SEARCH PAGE</a>

    </center>
    <div id="footerbottom">
        <div class="footerwrap">
            <div id="copyright">2015 - Designed By -Anand Dwivedi.<a href="http://learnjavabyanand.blogspot.in/" target="_blank"><img src="test.png" width="150" height="28" border="0"  /></a></div>

        </div>
    </div>
        <style type="text/css">
            .Head{
                background-color: #7a7a7a;
                position:absolute;
                top: -29px;
                width: 100%;
                left: -0.5;
                height: 50px;
                text-align: center;
                color: black;
                font-size: 30px;
                padding-top: 1%;
                margin-left: -13px;
            }
            .footerwrap{
                background-color: #7a7a7a;
                position:absolute;
                bottom:0;
                width:100%;
                left:  -0.5px;
                height:50px; 
                text-align: center;

            }
            .Header{
                text-align: center;
                text-decoration-color: deeppink;
                margin-top: 17%;
            }
            .bod{
                background-color:darkcyan;
                text-align: center;
                margin-top: 20%;
            }
        </style>
    </body>
</html>
===============================================
showBooks.jsp
===============================================
<%--
    Document   : newjspTest
    Created on : Aug 7, 2015, 3:42:52 PM
    Author     : ananddw
--%>


<%@ page import="java.util.*"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
    <title>|| Show Books ||</title>
    <body class="bod">
        <center>
            <h2 class="Head">Book Search</h2>
            <br></br>
            <font color="lightblue" size="6"> ${ADDED} </font>
        </center>
        <br />
        <%
            Object obj = request.getAttribute("MSG");
            if (obj != null) {
        %>
        <br />
        <center>
            <font color="lightgreen" size="6"><%=obj%></font> <br />
            <a href="index.jsp"> <h2>Go To Search Page</h2>
            </a>
        </center>
        <%
        } else {
            obj = session.getAttribute("Books");
            ArrayList<String> blist = (ArrayList<String>) obj;
            for (String bnm : blist) {
        %>
        <form action="addtocart.action" method="post">
            <input type="hidden" name="bname" value="<%=bnm%>" /> <font size="5"><%=bnm%>
                <input type="submit" value="Add to Cart" class="add">
            </font>
        </form>
        <%
            }
        %>
        <br />
        <form action="showcart.action">
            <input type="submit" value="Show Cart" class="But"/>
        </form>
        <%
            }
        %>

        <div id="footerbottom">
            <div class="footerwrap">
                <div id="copyright">2015 - Designed By -Anand Dwivedi.<a href="http://learnjavabyanand.blogspot.in/" target="_blank"><img src="test.png" width="150" height="28" border="0"  /></a></div>

            </div>
            <style type="text/css">
                .footerwrap{
                    background-color: #7a7a7a;
                    position:absolute;
                    bottom:0;
                    width:100%;
                    left:  -0.5px;
                    height:50px; 
                    text-align: center;

                }
                .Head{
                    background-color: #7a7a7a;
                    position:absolute;
                    top: -29px;
                    width: 100%;
                    left: -0.5;
                    height: 50px;
                    text-align: center;
                    color: black;
                    font-size: 30px;
                    padding-top: 1%;
                    margin-left: -13px;
                }
                .bod{
                    background-color:darkcyan;
                    text-align: center;
                    margin-top: 5%;
                }
                .But{
                    margin-top: 5%;
                    background-color: indianred;
                }
                .add{
                    background-color: lightskyblue;
                }
            </style>
    </body>
</html>
==============================================
showcart.jsp
==============================================
<%--
    Document   : newjspTest
    Created on : Aug 7, 2015, 3:48:02 PM
    Author     : ananddw
--%>

<%@ page import="java.util.*"%>
<html>
    <title>|| Show Cart||</title>
    <body  class="bod">
    <center>

        <h2 class="Head">Book Search</h2>
    </center>
    <%Object obj = request.getAttribute("MSG");
        if (obj != null) {
    %>
    <br/><center><font color="red" size="6"><%=obj%> </font></center>
        <%
        } else {
            obj = request.getAttribute("CART");
            ArrayList<String> blist = (ArrayList<String>) obj;
            for (String bnm : blist) {
        %>
    <form action="removefromcart.action" method="post">
        <input type="hidden" name="bname" value="<%=bnm%>"/>
        <font size="5"><%=bnm%><input type="submit"  value="Remove from CART" class="But"/></font>
    </form>
    <%
        }
    %>
    <br/>
    <center><a href="placeorder.jsp">PLACE ORDER</a></center>
        <%
            }
        %><center>
        <br/><a href="showbooks.jsp">ADD TO CART</a>
    </center>

    <div id="footerbottom">
        <div class="footerwrap">
            <div id="copyright">2015 - Designed By -Anand Dwivedi.<a href="http://learnjavabyanand.blogspot.in/" target="_blank"><img src="test.png" width="150" height="28" border="0"  /></a></div>

        </div>
        <style type="text/css">
            .Head{
                background-color: #7a7a7a;
                position:absolute;
                top: -29px;
                width: 100%;
                left: -0.5;
                height: 50px;
                text-align: center;
                color: black;
                font-size: 30px;
                padding-top: 1%;
                margin-left: -13px;
            }
            .footerwrap{
                background-color: #7a7a7a;
                position:absolute;
                bottom:0;
                width:100%;
                left:  -0.5px;
                height:50px; 
                text-align: center;

            }
            .bod{
                background-color:darkcyan;
                text-align: center;
                margin-top: 5%;
                float: left;
                padding-left: 38%;
                padding-top:10%;
            }
            .But{
                margin-top: 5%;
                background-color: indianred;
            }
        </style>
    </body>
</html>


======Server Side Code AddToCartServlet================
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.servlets;

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
/**
 *
 * @author ananddw
 */

public class AddToCartServlet extends HttpServlet {
     /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */

    protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        // Accessing the existing session object
        HttpSession sess = req.getSession(false);
        // Validating session are available or not
        if (sess == null) {
            req.setAttribute("MSG", "Session is Destroyed");
        } else {
            String bnm = req.getParameter("bname");
            // Accessing the client selected Book to session
            sess.setAttribute(bnm, bnm);
            req.setAttribute("ADDED", bnm + " is added to cart");
            System.out.println("Calling ADDtoCart Servlet Class ");
        }
        RequestDispatcher rd = req.getRequestDispatcher("showbooks.jsp");
        rd.forward(req, res);
        System.out.println("Request forward to Showbooks.jsp from Addtocard servlet class");
    }

}

======Server Side Code Loginservlet================

package com.servlets;

import java.io.IOException;
import java.io.Writer;
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;

public class Loginservlet extends HttpServlet {

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        System.out.println("Calling Method !!");
        //collecting the client submit the data
        String un = req.getParameter("UserName");
        String pwd = req.getParameter("Password");
        String msg = "";
        if (un.equals(pwd)) {
            msg = "<body bgcolor=darkgreen><h1 align=center><font color=red>Login success!!!!!!!!! Welcome to To Book Store </font></h1></body>";

        } else {
            msg = "Invlid login!!!Try again";
        }
       
        RequestDispatcher rd = req.getRequestDispatcher("index.jsp");
       
        rd.forward(req, res);
        System.out.println("Forward Sucessfully ");
        Writer out = res.getWriter();
        out.write(msg);
        HttpSession session = req.getSession();
        System.out.println("Session from Servlet Class===>"+session);
    }
}
======Server Side Code LogoutServlet================
package com.servlet;

import java.io.IOException;

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;
public class LogoutServlet extends HttpServlet {
    protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
    HttpSession sess=req.getSession(false);
    if(sess!=null)
        sess.invalidate();
    RequestDispatcher rd=req.getRequestDispatcher("logout.jsp");
    rd.forward(req, res);
    }

}
======Server Side Code MyContextListener================

package com.servlet;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class MyContextListener implements ServletContextListener {
      public void contextInitialized(ServletContextEvent event) {
    System.out.println("**ContextInitialized***");
    ServletContext ctx=event.getServletContext();
    ctx.setAttribute("TV", 0); 
    ctx.setAttribute("TA", 0); 
    }
    public void contextDestroyed(ServletContextEvent arg0) {
    System.out.println("***contextDestroyed**");
    }
   
}
======Server Side Code MySessionListener================


package com.servlets;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class MySessionListener implements HttpSessionListener {
    public void sessionCreated(HttpSessionEvent event) {
    HttpSession sess=event.getSession();
        System.out.println("session Called===>"+sess);
    ServletContext ctx=sess.getServletContext();
    int tv=(Integer) ctx.getAttribute("TV");
    tv++;
    ctx.setAttribute("TV", tv);
    int ta=(Integer) ctx.getAttribute("TA");
    ta++;
    ctx.setAttribute("TA", ta);
    }
    public void sessionDestroyed(HttpSessionEvent event) {
    HttpSession sess=event.getSession();
    ServletContext ctx=sess.getServletContext();
    int ta=(Integer) ctx.getAttribute("TA");
    ta--;
    ctx.setAttribute("TA",ta);
   
    }
   
}

======Server Side Code RemoveFromCartServlet================

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.servlets;

import java.io.*;
import java.util.*;

import javax.servlet.*;
import javax.servlet.http.*;
/**
 *
 * @author ananddw
 */

public class RemoveFromCartServlet extends HttpServlet {
     /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */
    protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        HttpSession sess = req.getSession(false);
        if (sess == null) {
            req.setAttribute("MSG", "Session is distroyed");
        } else {
            String bnm = req.getParameter("bname");
            // Removing the client selected book from session
            sess.removeAttribute(bnm);
                        System.out.println("Remove Book form Session");
        }
        RequestDispatcher rd = req.getRequestDispatcher("showcart.action");
        rd.forward(req, res);
                System.out.println("request forward to Showcart using RemoveFormCartServlet Class");
    }
       

}

======Server Side Code SearchBookServlet================

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.servlets;

import java.io.IOException;
import java.util.*;

import javax.servlet.*;
import javax.servlet.http.*;
/**
 *
 * @author ananddw
 */

public class SearchBookServlet extends HttpServlet {
     /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */

    protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        String cat = req.getParameter("category");
        if (cat != null && cat.equals("Java")) {
            ArrayList<String> blist = new ArrayList<String>();
            blist.add("Java");
            blist.add("Jdbc");
            blist.add("Servlet");
            blist.add("Jsp");
            blist.add("Ejb");
            blist.add("RMI");
            blist.add("HTML");
            HttpSession sess = req.getSession();
            System.out.println("Session Called?" + sess);
            sess.setAttribute("Books", blist);
            System.out.println("Session After set Attribute?" + sess);
        } else {
            req.setAttribute("MSG", "No books found with category" + cat);
        }
        RequestDispatcher rd = req.getRequestDispatcher("showbooks.jsp");
        rd.forward(req, res);
       
        System.out.println("Request Forward to showbooks.jsp page using SearchBooksServlet class");
    }

}

======Server Side Code SessionTrack================

 package com.servlets;


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 Infomation</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>");
    }
}
==================Server Side ShowCartServlet============

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package com.servlets;

import java.io.*;
import java.util.*;

import javax.servlet.*;
import javax.servlet.http.*;
/**
 *
 * @author ananddw
 */

public class ShowCartServlet extends HttpServlet {
     /**
     * Processes requests for both HTTP <code>GET</code> and <code>POST</code>
     * methods.
     *
     * @param request servlet request
     * @param response servlet response
     * @throws ServletException if a servlet-specific error occurs
     * @throws IOException if an I/O error occurs
     */

    protected void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        HttpSession sess = req.getSession();
        if (sess == null) {
            req.setAttribute("MSG", "Session is destroyed");
            RequestDispatcher rd = req.getRequestDispatcher("showbooks.jsp");
            rd.forward(req, res);
        } else {
            Enumeration<String> enms = sess.getAttributeNames();
            List<String> selectedlist = Collections.list(enms);
            selectedlist.remove("Books");
            if (selectedlist.size() == 0) {
                req.setAttribute("MSG", "No Books selected");
            } else {
                req.setAttribute("CART", selectedlist);
            }
            RequestDispatcher rd = req.getRequestDispatcher("showcart.jsp");
            rd.forward(req, res);
            System.out.println("Calling ShowCart Class and revert back on showcart.jsp");
        }
    }
   

}
=======================web.xml================
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
         id="WebApp_ID" version="2.5">
    <display-name>Lab18</display-name>
    <welcome-file-list>
        <welcome-file>Login.html</welcome-file>
    </welcome-file-list>
    <servlet>
        <servlet-name>SBServ</servlet-name>
        <servlet-class>com.servlets.SearchBookServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>SBServ</servlet-name>
        <url-pattern>/searchbook.action</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>ATocServ</servlet-name>
        <servlet-class>com.servlets.AddToCartServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>ATocServ</servlet-name>
        <url-pattern>/addtocart.action</url-pattern>
    </servlet-mapping>
    <servlet>

        <servlet-name>SCServ</servlet-name>
        <servlet-class>com.servlets.ShowCartServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>SCServ</servlet-name>
        <url-pattern>/showcart.action</url-pattern>
    </servlet-mapping>
    <servlet>

        <servlet-name>RemoveFromCartServlet</servlet-name>
        <servlet-class>com.servlets.RemoveFromCartServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>RemoveFromCartServlet</servlet-name>
        <url-pattern>/RemoveFromCartServlet</url-pattern>
    </servlet-mapping>
    <servlet>

        <servlet-name>RFCServ</servlet-name>
        <servlet-class>com.servlets.RemoveFromCartServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>RFCServ</servlet-name>
        <url-pattern>/removefromcart.action</url-pattern>
    </servlet-mapping>
    <servlet>
        <servlet-name>loginservlet</servlet-name>
        <servlet-class>com.servlets.Loginservlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>loginservlet</servlet-name>
        <url-pattern>/login.action</url-pattern>

    </servlet-mapping>
    <servlet>
        <servlet-name>logoutServ</servlet-name>
        <servlet-class>com.servlet.LogoutServlet</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>logoutServ</servlet-name>
        <url-pattern>/logout.action</url-pattern>
    </servlet-mapping>
    <listener>
        <listener-class>com.servlet.MyContextListener</listener-class>
    </listener>
    <listener>
        <listener-class>com.servlet.MySessionListener</listener-class>
    </listener>
</web-app>

How to Create PDF File Using Java Code

package com.anand;

import com.lowagie.text.Document;
import com.lowagie.text.Paragraph;
import com.lowagie.text.pdf.PdfWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
import java.util.Date;

public class GeneratePDF {

    public static void main(String[] args) {
        try {
            OutputStream file = new FileOutputStream(new File("/home/ananddw/test.pdf"));
            Document document = new Document();
            PdfWriter.getInstance(document, file);
            document.open();
            document.add(new Paragraph("welcome Anand in the World of PDF "));
          
            document.close();
            file.close();

        } catch (Exception e) {

            e.printStackTrace();
        }
    }
}
===============================================
Attach Some Require Jar else you will get error 

Thanks 
Anand Dwivedi

How to append Same File name With Date Append in Java?

Please Find Code Below :

==================Append.java=======================
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Date;

/**
 *
 * @author ananddw
 */
public class Append {

    public static void main(String[] args) throws IOException {
        /*

         Date date = new Date();
        File file1 = new File("/home/ananddw/Anand.json");
        String file2 = file1.getParent().toString();
        System.out.println("file 2 call ===>" + file2);
        boolean b = false;
        if (!(file1.exists())) {
            b = file1.createNewFile();
        }
        if (b) {
            System.out.println("Empty File successfully created");
        } else {

            String fileContent = "";
              String filename = file1.toString() + date;

            try {
                File f = new File(file1.toString());

                FileInputStream inp = new FileInputStream(f);

                byte[] bf = new byte[(int) f.length()];

                inp.read(bf);

                fileContent = new String(bf, "UTF-8");

                System.out.println("file===>" + fileContent);

            } catch (FileNotFoundException e) {

            } catch (IOException e) {
            }
            System.out.println("file name in else===>" + filename);
            FileWriter fw = new FileWriter(filename, true);
            System.out.println("FileWriter===>"+fw);
            String see = null;
            fw.write("Test");
            fw.close();
            System.out.println("Failed to create File");

        }

    }
}