Example of a Servlet

You will be creating each servlet as a Java class in a Dynamic Web Application in Eclipse. Here is an example of the code for a simple servlet. It prints 'Hello, World!' to the browser.

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

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class Hello
 */
@WebServlet("/Hello")
public class Hello extends HttpServlet {
    private static final long serialVersionUID = 1L;
    public Hello() {
        super();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)         
                                               throws ServletException, IOException {

        response.setContentType("text/html;charset=UTF-8");
        PrintWriter out = response.getWriter();
        try {
            out.println("<h1>Hello, World!</h1>");
        } finally {
            out.close();
        }
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request,response);
    }
}

Description

We notice two methods in this class: doGet() and doPost(). The first one anwsers by HTTP to the reception of a GET request. The second to the reception of a POST request. As we want that in the both cases the servlet processes the request, doPost() forwards to doGet().

Call the servlet from the browser

http://localhost:999/webTest/Greeting

Result in the browser:

Hello, World!

Mapping the Servlet to the URL

With Tomcat v. 7.0 and later you can use the @WebServlet annotation to map a servlet to a URL pattern. Simply code the URL pattern in parenthesis following the annotation, @WebServlet("/Hello").

Decomposition of the URL

Calling the servlet's URL from the browser will request the servlet. You can also call the servlet from a link or a form on a web page.

The URL parts of the URL: Protocol: http or https Domain: somedomain.com Port (optional): the port which the servlet listens to Root Entry Directory: the directory in which the servlet class file resides Servlet Name: from the annotation mapping [Protocol://][Domain]:[PORT]/[RootEntryDirectory]/[ServletName]

Example of a Servlet