JSP & Servlet

3 min readMar 6, 2021

Servlet

A servlet is a small Java program that runs within a Web server. Servlets receive and respond to requests from Web clients, usually across HTTP, the HyperText Transfer Protocol.

We can implement 2 types of interface.

javax.servlet.GenericServlet
javax.servlet.http.HttpServlet

Life Cycle of Servlet

First servlet is constructed, and initialized with init method.
Any calls from clients to the service method are handled.
When servlet is out of service, then destroy method is called for garbage collection.

Methods of Servlet

void destroy()- Used to indicate a servlet is taken out of service.
ServletConfig getServletConfig()- Returns object of ServletConfig which contains initialization and startup parameter.
java.lang.String getServletInfo()- Returns author, version and copyright of server.
void init(ServletConfig config)- Called by the servlet container to indicate to a servlet that the servlet is being placed into service.
void service(ServletRequest req, ServletResponse res)- Called by the servlet container to allow the servlet to respond to a request.

Example:-

import javax.servlet.http.*;
import javax.servlet.*;
import java.io.*;
public class DemoServlet extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse res)throws ServletException,IOException
{
res.setContentType(“text/html”);//setting the content typePrintWriter pw=res.getWriter();//get the stream to write data
pw.println(“<html><body>”);
pw.println(“Welcome to servlet”);
pw.println(“</body></html>”);
pw.close();//closing the stream
}}<web-app>
<servlet>
<servlet-name>Bhuvi</servlet-name>
<servlet-class>DemoServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Bhuvi</servlet-name>
<url-pattern>/welcome</url-pattern>
</servlet-mapping>
</web-app>

JSP

A JSP page is a text document that contains two types of text.

Static data, which can be expressed in any text-based format (such as HTML, SVG, WML, and XML).
JSP elements, which construct dynamic content.

JSP Tags

Declaration Tag:- Used to declare variables.

<%! int var=10; %>

2. Java Scriplets:- Used to add any type of java code.

<% 
String s="Kamesh";
System.out.println(s);
%>

3. JSP Expression:- Evaluates and convert the expression to a string.

<% num1=num1+num2 %>

4. Comments:- Used to add comment in code.

<% -- JSP Comments %>

JSP Life Cycle

Internally JSP page is converted into a servlet.
Compilation of JSP page.
Class loading means jsp.java file is converted into class file.
Instantiation means object of generated servlet class is created.
Initialization menas jsp init() method is invoked by container.
Request Processing means jsp service() method is invoked by container.
Destroy method is called for garbage collection.

Example:-

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ include file="admin.jsp"%>
<%@ page import="com.ContactPage.ConnectionProvider"%>
<%@ page import="java.sql.*"%>

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>DashBoard</title>
</head>
<body>
    <hr/>

    <form action="Archieve.jsp" method="post">
        <%
        response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate");
        if (session.getAttribute("session") == null) {
            response.sendRedirect("login.jsp");
        }
        try {
            Connection connection = ConnectionProvider.getConnection();
            Statement statement = connection.createStatement();
            String query = "Select * from contactus where isactive=true ORDER BY timestamp";
            ResultSet resultset = statement.executeQuery(query);
        %>
        <h1>Active Requests</h1>
        <table border="1">
            <tr>
                <td>Full Name</td>
                <td>E-Mail</td>
                <td>Message</td>
                <td>Time Zone</td>
            </tr>
            <%
            while (resultset.next()) {
            %>
            <tr>
                <td><%=resultset.getString(1)%></td>
                <td><%=resultset.getString(2)%></td>
                <td><%=resultset.getString(3)%></td>
                <td><%=resultset.getString(4)%></td>

                <td><input type="submit" value="Archieve"> <input
                    type="hidden" value=<%="Archieve" + resultset.getInt(6)%>
                    name="Archieve"></td>
                <%
                }
                } catch (Exception exception) {
                out.println(exception);
                }
                %>
            
        </table>
    </form>

    <br>
    <hr />
    <h1>Archive Requests</h1>
    <form action="UnArchieve.jsp" method="post">
        <%
        try {

            Connection connection = ConnectionProvider.getConnection();
            Statement statement = connection.createStatement();
            String query = "Select * from contactus where isactive='false' ORDER BY timestamp";
            ResultSet resultset = statement.executeQuery(query);
        %>
        <table border="1">
            <tr>
                <td>Full Name</td>
                <td>E-Mail</td>
                <td>Message</td>
                <td>Time Zone</td>
            </tr>
            <%
            while (resultset.next()) {
            %>
            <tr>
                <td><%=resultset.getString(1)%></td>
                <td><%=resultset.getString(2)%></td>
                <td><%=resultset.getString(3)%></td>
                <td><%=resultset.getString(4)%></td>
                <td><input type="submit" value="UnArchieve"> <input
                    type="hidden" value=<%="UnArchieve" + resultset.getInt(6)%>
                    name="unArchieve"></td>

            </tr>
            <%
            }
            } catch (Exception exception) {
            out.println(exception);
            }
            %>
        </table>
    </form>
</body>
</html>

Output:-

Conclusion

When ever we compile JSP it is converted into servlet. So there is no real time difference. But usually there is a tradition to use servletes for controllers and JSPs for views. Controllers are like java classes so we can get full tool support from our favorate IDEs.

JSP & Servlet

Servlet

JSP

JSP Life Cycle

Conclusion

Written by Kamesh Shekhar Prasad