How to Run Servlet in Tomcat?

In this example, we will create a basic servlet that displays a Hello World message from a Java program to the user in the browser without using any Java IDE like Eclipse.

Note:

Running a server like Tomcat to run our servlet. if it is not already installed, you can install it using this article: How to Install Apache Tomcat on Windows?

Basic Terms

GenericServlet

A servlet class is usually created by extending either the GenericServlet class or its descendant javax.servlet.http.HttpServlet class.
The GenericServlet class defines a generic protocol-independent servlet, in the sense that it can be extended to provide
implementation of any protocol, such as HTTP, FTP, and SMTP.
It provides implementations of the life cycle methods init() and destroy(), as well as methods in the ServletConfig interface.

HttpServlet

Provides a framework for handling HTTP requests.
It provides an implementation for the service() method.
The service() method in the HttpServlet class reads the method type stored in the HTTP request message and invokes a specific method based on this value.
Specifically, if the method type is GET, it calls doGet(); if the method type is POST, it calls doPost(); and so on. These are the methods that we need to override.

Steps For Creating Servlet

Our servlet is a simple servlet designed to handle the HTTP GET method.
Create the following servlet HelloWorldServlet.java using any text editor like Notepad.

Java

import java.io.*; 

import javax.servlet.*; 

import javax.servlet.http.*; 

public class HelloWorldServlet extends HttpServlet { 

    public void doGet(HttpServletRequest request, 

                      HttpServletResponse response) 

        throws IOException, ServletException 

    { 

        response.setContentType("text/html"); 

        PrintWriter out = response.getWriter(); 

        out.println( 

            "<html><head><title>Hello World Servlet</title></head>"); 

        out.println("<body>"); 

        out.println("<h1>Hello World!</h1>"); 

        out.println("</body></html>"); 

        out.close(); 

    } 
}

The class HelloWorldServlet extends the HttpServlet class.
It is written to handle only the GET method. Therefore, only the doGet() method is overridden.
Finally, it sends the following HTML document.

HTML

<html> 

   <head> 

      <title>Hello World Servlet</title> 

   </head> 

   <body> 

      <h1>Hello World!</h1> 

   </body> 

</html>

Here we are assuming we have installed Tomcat in the D directory of our computer.

Building and Installing Servlet

To compile our HelloWorldServlet.java file, servlet class files are required.
Tomcat comes with a .jar file (servlet-api.jar) that contains necessary class files
You can find this jar file usually in the TOMCAT_HOME\lib directory

Compile the HelloWorldServlet.java using the following command in the Command Prompt and press enter:

javac HelloWorldServlet.java

This generates the file HelloWorldServlet.class that contains the byte code for our servlet.
Create the following directory structure under the webapps subdirectory

Put the HelloWorldServlet.class file in the TOMCAT_HOME\webapps\net\WEB-INF\classes directory.
Inform the web server about the existence of this servlet and the URL that will be used to refer to this servlet
Specify in the TOMCAT_HOME\net\WEB-INF\web.xml file,

XML

<servlet> 

     <servlet-name>HelloWorld</servlet-name> 

     <servlet-class>HelloWorldServlet</servlet-class> 

</servlet> 

<servlet-mapping> 

     <servlet-name>HelloWorld</servlet-name> 

     <url-pattern>/servlet/HelloWorld</url-pattern> 

</servlet-mapping>

Accessing the servlet

The complete URL of this servlet will be http://172.16.5.81:8080/net/servlet/HelloWorld where 8080 is the port number.
Type the following URL in the address bar of your web browser and press enter

http://172.16.5.81:8080/net/servlet/HelloWorld

Article Tags :

Java

Web Technologies