I have made a program for insertion, viewing, deletion, updation of stored data in database. 

But since last 3-4 hours I am getting error :- javax.servlet.ServletException: Servlet execution threw an exception

I know what the mistake is, every time I make blunder in web.xml file. As I am always confused with configuring web.xml file. So I get "resource not available error" can any one help me with it. I have posted the web.xml file
Can any one help me with solving this problem ??

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" version="2.5">
  <display-name></display-name>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>MyServlet</servlet-class>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>DataInsert</servlet-name>
    <servlet-class>DataInsertTable</servlet-class>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>DataUpdate</servlet-name>
    <servlet-class>DataUpdateTable</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>MyServlet</servlet-name>
    <url-pattern>/MyServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>DataInsert</servlet-name>
    <url-pattern>/DataInsert</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>DataUpdate</servlet-name>
    <url-pattern>/DataUpdate</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

```

This is my code :- 

index.jsp

```
<html>
    <head>
        <title>Data insertion form</title>
    </head>

    <body>

    <%
    String action="/SimpleServlet/DataInsertTable";
    String method="get";

    if(request.getAttribute("EDIT")!=null)
    {
        action="/SimpleServlet/DataUpdateTable";
        method="post";
    }

    %>

    <form method= "<%=method%>" action="<%=action%>">

    <h1><center>Enter the required information</center></h1>

    <table>
        <tr>
            <td>Name</td>
            <td> :- </td>
            <%if(request.getAttribute("NAME")!=null){ %>
            <td><input type="text" name="name" value="<%=request.getAttribute("NAME")%>"></input>

            <%}else{ %>
            <td><input type="text" name="name"></input>
            <%} %>
            </td>
        </tr>

        <tr>
            <td>Roll Number</td>
            <td> :- </td>
           <%if(request.getAttribute("ROLL")!=null){ %>
            <td><input type="text" name="roll" value="<%=request.getAttribute("ROLL")%>"></input>

            <%}else{ %>
            <td><input type="text" name="roll"></input>
            <%} %>
            </td>       
        </tr>

        <tr>
            <td>Class </td>
            <td> :- </td>
             <%if(request.getAttribute("CLAS")!=null){ %>
            <td><input type="text" name="clas" value="<%=request.getAttribute("CLAS")%>"></input>

            <%}else{ %>
            <td><input type="text" name="clas"></input>
            <%} %>
            </td>
        </tr>

        <tr>
            <td>Mobile Number </td>
            <td> :- </td>
            <%if(request.getAttribute("MONO")!=null){ %>
            <td><input type="text" name="mono" value="<%=request.getAttribute("MONO")%>"></input>

            <%}else{ %>
            <td><input type="text" name="mono"></input>
            <%} %>
            </td>
        </tr>

        <tr>
            <td></td>
            <td><input type="submit" value="Submit" width="16"></input></td>
        </tr>

    </table>

    </form>

    </body>
</html>

```

DataInsertTable.java

```
import java.io.*; 

import java.sql.*; 

import javax.servlet.*; 

import javax.servlet.http.*; 

public class DataInsert extends HttpServlet {
    public void doGet(HttpServletRequest req, HttpServletResponse res)
    throws IOException, ServletException    {

        res.setContentType("text/html");
        PrintWriter out = res.getWriter();
        PrintWriter pwinsert = res.getWriter();
//      PrintWriter pwdelete = res.getWriter(); 

        Connection con = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        Statement st = null;

        out.println("<html>");
            out.println("<head>");
                out.println("<title>User Data</title>"); 
            out.println("</head>"); 

            out.println("<body>"); 

            out.println("<center><u><h1>User Data</h1></u>"); 

            out.println("<form name='form' >"); 

            int a = 2; 
            out.println("<table border="+a+ "> "); 

            out.println("<tr>"); 
                out.println("<td> Select </td>"); 
                out.println("<td> Name </td>"); 
                out.println("<td> Roll No. </td>"); 
                out.println("<td> Class </td>"); 
                out.println("<td> Mobile Number </td>"); 
                out.println("<td> Edit </td>"); 
            out.println("</tr>"); 

            String nm = req.getParameter("name"); 
            String roll = req.getParameter("roll"); 
            String clas = req.getParameter("clas"); 
            String mono = req.getParameter("mono");

            try {
                Class.forName("oracle.jdbc.driver.OracleDriver");
            }
            catch(ClassNotFoundException ex)    {
                System.out.println("driver not loaded");
                System.exit(0); 
            } 

            String URL = "jdbc:oracle:thin:@192.168.106.87:1521:ORA11G";
            String Username = "pratik";
            String Password = "pratik";

            try {
                con = DriverManager.getConnection(URL,Username,Password); 

                if(req.getParameter("choise")==null)    {
                    ps = con.prepareStatement("INSERT INTO student (name, rollno, class, mobileno) VALUES (?, ?, ?, ? )"); 
                    ps.setString(1,nm);
                    ps.setString(2,roll); 
                    ps.setString(3,clas); 
                    ps.setString(4,mono); 

                    int i = ps.executeUpdate(); 
                    pwinsert.println(i); 

                    if(i!=0)    { 
                        pwinsert.println("Your data has been stored in the database"); 
                    } 
                    else    { 
                        pwinsert.println("Your data could not be stored in the database"); 
                    } 
                }
            } 
            catch(Exception e)  {
                pwinsert.println(e.getMessage());
            } 

            String idr=null;

            if(req.getParameter("choise")!=null)    {
                nm = req.getParameter("choise");
                idr = "DELETE from student WHERE name ='"+nm+"'"; 

                try {
                    st=con.createStatement(); 
                    rs = st.executeQuery(idr); 
                } 
                catch (Exception e) { 
                    e.getMessage(); 
                    System.out.println("Error " +e); 
                } 

                System.out.println("Data deleted..."); 
            }

//          res.sendRedirect("DataInsertTable.java"); 

            idr = "SELECT * FROM student"; 

            try {
                st=con.createStatement(); 
                rs = st.executeQuery(idr); 
            }
            catch (Exception e) { 
                e.getMessage(); 
                System.out.println("Error " +e); 
            } 

            try { 
                while (rs.next())   { 
                    out.println("<tr>"); 
                        out.println("<td>" + "<input type=\"radio\" name=\"choise\" value=\"" + rs.getString(1) + "\" /> </br>" + "</td>");
                        out.println("<td>" + rs.getString(1) + "</td>" + "\t <td>" + rs.getInt(2) + "</td>" + "\t <td>" + rs.getString(3) + "</td>" + "\t <td>" + rs.getString(4)); 
                        out.println("<td>" + "<a href='"+req.getContextPath()+"/DataUpdate?mode=EDIT&name="+rs.getString(1)+"&roll="+rs.getInt(2)+"&clas="+rs.getString(3) +"&mono="+rs.getString(4)+"'>Edit</a> </br>" + "</td>"); 
                    out.println("</tr>"); 
                } 

                out.println("<tr>"); 
                    out.println("<td> </td>"); 
                    out.println("<td> </td>"); 
                    out.println("<td>" + "<input type=\"submit\" value=\"Delete\" />" + "</td>");
                    out.println("<td> </td>"); 
                    out.println("<td> </td>"); 
                out.println("</tr>"); 
            } 
            catch (Exception e) { 
                e.getMessage(); 
                System.out.println("Error" +e); 
            } 

            try { 
                rs.close(); 
            } 
            catch (Exception e) { 
                e.getMessage(); 
                System.out.println("Error" +e); 
            } 

            try { 
                st.close(); 
            } 
            catch (Exception e) { 
                e.getMessage(); 
                System.out.println("Error" +e); 
            } 

            out.println("</table>"); 
            out.println("</form>"); 
            out.println("</center>"); 
            out.println("</body>"); 
            out.println("</html>"); 
            out.close(); 

    } 
}

```

DataUpdateTable.java

```
import java.io.*; 
import java.sql.*; 
import javax.servlet.*; 
import javax.servlet.http.*; 

public class DataUpdateTable extends HttpServlet    {
    public void doGet(HttpServletRequest req, HttpServletResponse res)
    throws IOException, ServletException    { 

        res.setContentType("text/html"); 
        PrintWriter out = res.getWriter(); 
        PrintWriter pwinsert = res.getWriter(); 
//      PrintWriter pwdelete = res.getWriter(); 

        Connection con = null; 
        PreparedStatement ps = null; 
        ResultSet rs = null; 
        Statement st = null; 

        out.println("<html>"); 
            out.println("<head>"); 
                out.println("<title>User Data</title>"); 
            out.println("</head>"); 

            out.println("<body>"); 
                out.println("<center><u><h1>User Data</h1></u>"); 

                out.println("<form name='form' >"); 

                int a = 2; 
                out.println("<table border="+a+ "> "); 
                out.println("<tr>"); 
                    out.println("<td> Name </td>"); 
                    out.println("<td> Roll No. </td>"); 
                    out.println("<td> Class </td>"); 
                    out.println("<td> Mobile Number </td>"); 
                out.println("</tr>"); 

                String nm = req.getParameter("name"); 
                String roll = req.getParameter("roll"); 
                String clas = req.getParameter("clas"); 
                String mono = req.getParameter("mono"); 

                req.setAttribute("NAME", nm);
                req.setAttribute("ROLL", roll);
                req.setAttribute("CLAS", clas);
                req.setAttribute("MONO", mono);
                req.setAttribute("EDIT", "Y");

                req.getRequestDispatcher("/index.jsp").forward(req, res);

    }

    public void doPost(HttpServletRequest req, HttpServletResponse res)
    throws IOException, ServletException    {

        res.setContentType("text/html"); 
        PrintWriter out = res.getWriter(); 
        PrintWriter pwinsert = res.getWriter(); 
//      PrintWriter pwdelete = res.getWriter(); 

        Connection con = null; 
        PreparedStatement ps = null; 
        ResultSet rs = null; 
        Statement st = null; 

        try { 
            Class.forName("oracle.jdbc.driver.OracleDriver"); 
        } 
        catch(ClassNotFoundException ex)    { 
            System.out.println("driver not loaded"); 
            System.exit(0); 
        } 

        String URL = "jdbc:oracle:thin:@192.168.106.87:1521:ORA11G";
        String Username = "pratik";
        String Password = "pratik";

        try { 
            con = DriverManager.getConnection(URL,Username,Password); 

            String nm = req.getParameter("name"); 
            String roll = req.getParameter("roll"); 
            String clas = req.getParameter("clas"); 
            String mono = req.getParameter("mono"); 

            if(req.getParameter("choise")==null)    {
                ps = con.prepareStatement("update student set name=?, rollno=?, class=?, mobileno=? where rollno=?"); 
                ps.setString(1,nm); 
                ps.setString(2,roll); 
                ps.setString(3,clas); 
                ps.setString(4,mono); 
                ps.setString(5,roll); 

                int i = ps.executeUpdate(); 
                pwinsert.println(i); 

                if(i!=0)    {
                    pwinsert.println("Your data has been stored in the database"); 
                } 
                else    { 
                    pwinsert.println("Your data could not be stored in the database"); 
                } 
            }
        } 
        catch(Exception e)  { 
            pwinsert.println(e.getMessage()); 
        } 
    }
}

```