Java Servlet Quick Start Guide for Beginners (Tomcat + XML configuration)

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Last Updated on 11 March 2020   |   Print  Email


Table of content:

    1. A brief overview of Java servlet
    2. Creating directory structure
    3. Writing servlet class
    4. Writing JSP page
    5. Declaring and configuring mapping for the servlet in web.xml
    6. Compiling the servlet
    7. Packaging the web application
    8. Deploying the web application
    9. Testing the servlet

This tutorial is designed for those who are new to Java servlet and wish to learn Java servlet quickly by following a hands-on exercise without using an IDE. Assuming you have the following pieces of software installed on your computer (of course you can use newer versions):

And a simple text editor such as JEdit or Notepad++.

 

1. A brief overview of Java servlet

A servlet is a server-side component written in Java programming language that receives requests from client and sends responses back.

Servlet is the key component that forms a typical Java EE application, beside JSP, EJB, XML and other related technologies. A Java EE application can be packaged in a WAR file (Web ARchive) in order to be deployed on a web server. A web server that can run Java servlet is called a servlet container. The most popular and widely used servlet containers are Apache Tomcat, Glassfish, JBoss, etc.

Technically, a servlet is a normal Java class that extends either:

In practice, servlet is mostly used for handling HTTP requests, by overriding the HttpServlet’s doGet(), doPost() methods to handle GET and POST requests, respectively. The servlet container supplies an HttpServletRequest object and an HttpServletResponse object for dealing with the request and response.

Servlet is usually used in conjunction with JSP for generating dynamic content based on client’s requests. A typical scenario would be:


2. Creating directory structure

To get started, create the following directory structure:

directory structure


3. Coding the Java Servlet class

Create a Java source file called QuickServlet.java under the directory src\net\codejava\servlet with the following code:

package net.codejava.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletConfig;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class QuickServlet extends HttpServlet {

	/**
	 * this life-cycle method is invoked when this servlet is first accessed
	 * by the client
	 */
	public void init(ServletConfig config) {
		System.out.println("Servlet is being initialized");
	}

	/**
	 * handles HTTP GET request
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws IOException {

		PrintWriter writer = response.getWriter();
		writer.println("<html>Hello, I am a Java servlet!</html>");
		writer.flush();
	}

	/**
	 * handles HTTP POST request
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws IOException {
		String paramWidth = request.getParameter("width");
		int width = Integer.parseInt(paramWidth);

		String paramHeight = request.getParameter("height");
		int height = Integer.parseInt(paramHeight);

		long area = width * height;

		PrintWriter writer = response.getWriter();
		writer.println("<html>Area of the rectangle is: " + area + "</html>");
		writer.flush();

	}

	/**
	 * this life-cycle method is invoked when the application or the server
	 * is shutting down
	 */
	public void destroy() {
		System.out.println("Servlet is being destroyed");
	}
}

This servlet overrides four methods from the HttpServlet class:

      • HttpServletRequest: this object wraps all HTTP request headers so we can access GET/POST parameters as well as other HTTP headers sent from the client, via the methods getParameter() and getHeader(), respectively.
      • HttpServletResponse: we use this object to deal with HTTP response such as setting HTTP response headers and sending HTML content back to the client. In this servlet’s doGet() method, we send a simple HTML code which conveys a message “Hello, I am a Java servlet!” to the client.

 

4. Coding JSP page

Create a JSP file called index.jsp under the directory WebContent with the following HTML code: 

<html>
<head>
	<title>Quick Servlet Demo</title>
</head>
<body>
	<a href="/QuickServlet">Click here to send GET request</a> 
	
	<br/><br/>
	
	<form action="QuickServlet" method="post">
		Width: <input type="text" size="5" name="width"/> 
		&nbsp;&nbsp;
		Height <input type="text" size="5" name="height"/>
		&nbsp;&nbsp;
		<input type="submit" value="Calculate" />
	</form>
</body>
</html>

In this JSP page:

The JSP page would look like this in the browser:

Form in JSP page


5. Declaring and configuring mapping for the servlet in web.xml

In order to have the servlet be able to serving client’s requests, you have to declare and configure mapping for the servlet in web deployment descriptor file. Create an XML file called web.xmlunder the directory WebContent\WEB-INF with the following XML code:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	id="WebApp_ID" version="3.0">
	
	<display-name>Quick Servlet Demo Application</display-name>
	
	<servlet>
		<servlet-name>QuickServlet</servlet-name>
		<servlet-class>net.codejava.servlet.QuickServlet</servlet-class>
	</servlet>
  
	<servlet-mapping>
		<servlet-name>QuickServlet</servlet-name>
		<url-pattern>/QuickServlet</url-pattern>
	</servlet-mapping>  
	
</web-app>

As we can see, the servlet is declared using the <servlet> element and its children:

And the servlet is configured to serving requests using the <servlet-mapping> element and its children:


6. Compiling the servlet

Before doing the compilation, make sure you set the PATH environment variable includes the JDK_HOME\bin directory, so that the tools javac and jar can be accessed in the command line prompt.

In order to compile the servlet source code, we must have a servlet API jar file available in the classpath. The servlet API jar file usually provided by the servlet container. In case of Tomcat 7.0, the jar file is placed under TOMCAT_HOME\lib directory and is named as servlet-api.jar.

Open a command line utility of the operating system and change the working directory to the directory QuickServlet as outlined in the directory structure. Type the following command:

javac -cp TOMCAT_HOME\lib\servlet-api.jar" -d CLASS_DIRSRC_DIR\QuickServlet.java

Replace the names TOMCAT_HOME, CLASS_DIR and SRC_DIR with the following values:

That command will compile the QuickServlet.java file and place the generated .class file into the directory WebContent\WEB-INF\classes.

 

7. Packaging the web application

The standard way to deploy a Java EE application is packaging it as a WAR file which can be deployed on a web server. At command prompt, type the following command (note that there is a dot at the end):

jar cfv deploy\QuickServletApp.war -C WebContent .

The jar program will put everything in the directory WebContent into a single zip-format archive called QuickServletApp.war under the directory deploy.


8. Deploying the web application

Now we are ready to deploy the QuickServletApp.war file on Tomcat server. Copy it to Tomcat’s webapps directory:

copy deploy\QuickServletApp.war TOMCAT_HOME\webapps

Start Tomcat by executing the Tomcat7.exe program under TOMCAT_HOME\bin directory:

start Tomcat

From the logging in the console, we can see that the file QuickServletApp.war is deployed and the HTTP server is listening on the port number 8080.

 

9. Testing the servlet

Now open a web browser and type the following URL into the address bar:

http://localhost:8080/QuickServletApp

Because we don’t specify a specific page so the default page (index.jsp) is loaded as seen below:

Form in JSP page

To test the servlet with an HTTP GET request, click on the hyperlink “Click here to send GET request”. The following screen is displayed:

Test servelt with GET request

To test the servlet with an HTTP POST request, click browser’s back button and enter two numbers into the text fields width and height:

Enter numbers

Click on the Calculate button, the servlet will return the computed area as the result:

result of area

So far we have gone through the journey with Java servlet from scratch. We have the project available for download in the attachment section.

 

Other Java Servlet Tutorials:


About the Author:

is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.

Attachments:
Download this file (QuickServlet.zip)QuickServlet.zip[ ]6 kB