Java Cookbook

First Servlet: Generating an HTML Page

Problem

You want a servlet to present some information to the user.

Solution

Override the HttpServlet method service( ), or doGet( )/doPost( ).

Discussion

The abstract class javax.servlet.Servlet is designed for those who wish to structure an entire web server around the servlet notion. For example, in Sun’s Java Web Server, there is a servlet subclass for handling plain HTML pages, another for processing CGI programs, and so on. Unless you are writing your own web server, you will probably not extend from this class, but rather its subclass HttpServlet , in the package javax.servlet.http . This class has a method:

public void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException;

The service method is passed two arguments, request and response. The request contains all the information about the request from the browser, including its input stream should you need to read data. The response argument contains information to get the response back to the browser, including the output stream to write your response back to the user.

But the web has several HTTP methods for passing data into a web page. Unimportant for plain HTML pages, this distinction becomes of interest when processing forms, i.e., web pages with fill-in-the-blank or choice items. Briefly, the GET method of HTTP is used to pass all the form data appended to the URL. GET URLs look like this, for example:

http://www.acmewidgets.com/cgi-bin/ordercgi?productId=123456 ...