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Deleting All Rows From the database Table

                         

Consider a situation where we have entered some wrong data and in later situation it starts giving problem to an organization or may become useless after sometime . Rather than go through with that data its better to delete that data. We can do it very easily through our program, what we need is a simple query. 

In this example we are going to exactly the same as we said above. To make this possible we need to make a class named ServletDeletingAllRowsFromTable,  the name of the program should be such,  if in future there is any need to make any change in the program, you can easily understand in which program you have to make a change. As we know that in Servlet the main logic of the program is written inside the service method and in turn the service method calls the doGet() method. Now inside the doGet() method use the getWriter() method of the response object and its returns the PrintWriter object, which helps us to write on the browser. To delete all the rows from our database table there is a need for the connection between the database and the java program.  After the establishment of the connection with the database, fire a query for deleting all the rows in the database table. This query will be fired inside the prepareStatement() method of the Connection object and returns the PreparedStatement object. If the rows has been deleted from the database table then print the message "all rows are deleted" otherwise "no rows has been deleted".

The code of the program is given below: 

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

public class ServletDeletingAllRowsFromTable extends HttpServlet{
  public void doGet(HttpServletRequest request, HttpServletResponse response)
                    
throws  ServletException, IOException{
    response.setContentType("text/html");
    PrintWriter pw = response.getWriter();
    String connectionURL = "jdbc:mysql://localhost/zulfiqar";
    Connection connection;
    try{
      Class.forName("org.gjt.mm.mysql.Driver");
      connection = DriverManager.getConnection(connectionURL, "root""admin");
      PreparedStatement pst = connection.prepareStatement("delete from emp_sal");
      int i = pst.executeUpdate();
      if (i==0){
        pw.println("All rows are deleted");
      }
      else{
        pw.println("no rows has been deleted");
      }
    }
    catch(Exception e){
      pw.println("The exception is " + e);
    }
  }
}

XML File for this program:

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
 PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>
 <servlet>
 <servlet-name>Zulfiqar</servlet-name>
 <servlet-class>ServletDeletingAllRowsFromTable</servlet-class>
 </servlet>
 <servlet-mapping>
 <servlet-name>Zulfiqar</servlet-name>
 <url-pattern>/ServletDeletingAllRowsFromTable</url-pattern>
 </servlet-mapping>
</web-app>

Table in the database before deletion:

mysql> select * from emp_sal;
+----------+--------+
| EmpName | salary |
+----------+--------+
| zulfiqar | 15000 |
| vinod | 12000 |
+----------+--------+
2 rows in set (0.00 sec)

The output of the program is given below: 

Table in the database after deletion:

mysql> select * from emp_sal;
Empty set (0.02 sec)

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