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);
}
}
}
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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) |
Download this
example
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