Improving Servlet Performance to Fetch Records From Database
Here we will be boosting the web application’s ability to retrieve records from the database. To provide this, we save the table’s data in a collection and reuse that collection in our servlet. As a result, we aren’t repeatedly querying the database. We are enhancing our performance as a result of this. In order to begin, we must first generate the following table:
Table:
CREATE TABLE gfguser
(
userid INT,
username VARCHAR(50),
userpass VARCHAR(50),
useremail VARCHAR(100),
usercountry VARCHAR(50),
contact INT,
PRIMARY KEY (USERID)
)
Now, inside the table, add the following records.
Implementation: In this case, we’ve generated the following six resources:
- index.html
- User.java
- MainListenerGfg.java
- Servlet1.java
- servlet2.java
- web.xml
Two links in the index.html file transmit requests to the servlet. User.java is a straightforward bean class with three attributes and their associated getters and setters. The database table is represented by this class. The listener class is MainListenerGfg.java. The contextInitialized method of ServletContextListener is called by default when the project is deployed. We are retrieving the table’s records and saving them in the User class object, which has been added to the ArrayList class object. Lastly, the ArrayList class object will be used to hold all of the table’s records (collection).
Finally, we save the ArrayList object as an attribute in the ServletContext object so that we can utilize it in the servlet. Servlet1.java retrieves and outputs information from the servlet context object. Servlet2.java is identical to Servlet1.java. The information from the servlet context object is printed by this servlet. Information regarding servlets and listeners may be found in web.xml.
A. index.html
Java
<html>
<body>
<h1> GeeksForGeeks</h1>
<a href= "servlet1" >This is first servlet</a>|
<a href= "servlet2" >This is second servlet</a>
</body>
</html>
|
B. User.java
Java
public class User {
private int id;
private String name, password;
public int getId() { return id; }
public void setId( int id) { this .id = id; }
public String getName() { return name; }
public void setName(String name) { this .name = name; }
public String getPassword() { return password; }
public void setPassword(String password)
{
this .password = password;
}
}
|
C. MainListenerGfg.java
Java
import java.sql.*;
import java.util.ArrayList;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class MainListenerGfg
implements ServletContextListener {
public void contextInitialized(ServletContextEvent e)
{
ArrayList list = new ArrayList();
try {
Class.forName( "com.mysql.jdbc.Driver" );
Connection con = DriverManager.getConnection(
"root" , "root" );
PreparedStatement ps = con.prepareStatement(
"select * from gfguser" );
ResultSet rs = ps.executeQuery();
while (rs.next()) {
User u = new User();
u.setId(rs.getInt( 1 ));
u.setName(rs.getString( 2 ));
u.setPassword(rs.getString( 3 ));
list.add(u);
}
con.close();
}
catch (Exception ex) {
System.out.print(ex);
}
ServletContext context = e.getServletContext();
context.setAttribute( "data" , list);
}
public void contextDestroyed(ServletContextEvent arg0)
{
System.out.println( "project undeployed..." );
}
}
|
D.Servlet1.java
Java
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Iterator;
import java.util.List;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Servlet1 extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType( "text/html" );
PrintWriter out = response.getWriter();
long before = System.currentTimeMillis();
ServletContext context = getServletContext();
List list = (List)context.getAttribute( "data" );
Iterator itr = list.iterator();
while (itr.hasNext()) {
User u = (User)itr.next();
out.print( "<br>" + u.getId() + " " + u.getName()
+ " " + u.getPassword());
}
out.close();
}
}
|
E. Servlet2.java
Java
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Iterator;
import java.util.List;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Servlet2 extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException
{
response.setContentType( "text/html" );
PrintWriter out = response.getWriter();
long before = System.currentTimeMillis();
ServletContext context = getServletContext();
List list = (List)context.getAttribute( "data" );
Iterator itr = list.iterator();
while (itr.hasNext()) {
User u = (User)itr.next();
out.print( "<br>" + u.getId() + " " + u.getName()
+ " " + u.getPassword());
}
out.close();
}
}
|
F. web.xml
XML
< web-app >
< listener >
< listener-class >MainListenerGfg</ listener-class >
</ listener >
< servlet >
< servlet-name >Servlet1</ servlet-name >
< servlet-class >Servlet1</ servlet-class >
</ servlet >
< servlet >
< servlet-name >Servlet2</ servlet-name >
< servlet-class >Servlet2</ servlet-class >
</ servlet >
< servlet-mapping >
< servlet-name >Servlet1</ servlet-name >
< url-pattern >/servlet1</ url-pattern >
</ servlet-mapping >
< servlet-mapping >
< servlet-name >Servlet2</ servlet-name >
< url-pattern >/servlet2</ url-pattern >
</ servlet-mapping >
</ web-app >
|
Output:
In order to receive the following output, run the index.html file:
We will get the following result if you click on the “This is first servlet” link:
The following output will appear when you click on the “This is second servlet” link:
Last Updated :
05 Apr, 2022
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