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>| //first link <a href="servlet2">This is second servlet</a> //second link</body></html> |
B. User.java
Java
// Java Program to Illustrate User Class// Classpublic class User { // Declaring variables to // access data from database private int id; private String name, password; // Adding getters and setter for variables // Getters and Setters 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
// Java Program to Illustrate MainListener Class// Importing required classesimport java.sql.*;import java.util.ArrayList;import javax.servlet.ServletContext;import javax.servlet.ServletContextEvent;import javax.servlet.ServletContextListener;// Class// implementing ServletContextListener interfacepublic class MainListenerGfg implements ServletContextListener { // Method 1 public void contextInitialized(ServletContextEvent e) { // Creating an empty ArrayList ArrayList list = new ArrayList(); // Try block to check for exceptions try { // Loading drivers by // connecting with database Class.forName("com.mysql.jdbc.Driver"); Connection con = DriverManager.getConnection( "root", "root"); PreparedStatement ps = con.prepareStatement( "select * from gfguser"); ResultSet rs = ps.executeQuery(); // Accessing all data until its empty // using next() method 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); } // Closing the connections // using close() method con.close(); } // Catch block to handle exceptions catch (Exception ex) { // Displaying the exceptions System.out.print(ex); } // Storing the ArrayList object in ServletContext ServletContext context = e.getServletContext(); context.setAttribute("data", list); } // Method 2 public void contextDestroyed(ServletContextEvent arg0) { // Print statement whenever this method is called System.out.println("project undeployed..."); }} |
D.Servlet1.java
Java
// Java Program to Illustrate Servlet Class// Importing required classesimport 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;// Class// Extending HttpServlet Classpublic class Servlet1 extends HttpServlet { // Method 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(); // Condition holds true till there is single element // remaining in the List while (itr.hasNext()) { User u = (User)itr.next(); out.print("<br>" + u.getId() + " " + u.getName() + " " + u.getPassword()); } // Closing the connections // using close() method out.close(); }} |
E. Servlet2.java
Java
// Java Program to Illustrate Servlet Class// Importing required classesimport 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;// Class// Extending HttpServlet classpublic class Servlet2 extends HttpServlet { // Method 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 Iterator itr = list.iterator(); // Condition holds true till // there is single element remaining while (itr.hasNext()) { User u = (User)itr.next(); out.print("<br>" + u.getId() + " " + u.getName() + " " + u.getPassword()); } // Closing the connections // using close() method 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:
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