Page Generation
The most basic type of HTTP servlet generates a full HTML page. Such a servlet has access to the same information usually sent to a CGI script, plus a bit more. A servlet that generates an HTML page can be used for all the tasks where CGI is used currently, such as for processing HTML forms, producing reports from a database, taking orders, checking identities, and so forth.
Writing Hello World
Example 2.1 shows an HTTP servlet that generates a complete HTML page. To keep things as simple as possible, this servlet just says " Hello World” every time it is accessed via a web browser.[3]
Example 2-1. A servlet that prints “Hello World”
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HelloWorld extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException {
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<HTML>");
out.println("<HEAD><TITLE>Hello World</TITLE></HEAD>");
out.println("<BODY>");
out.println("<BIG>Hello World</BIG>");
out.println("</BODY></HTML>");
}
}This servlet extends the HttpServlet class and
overrides the doGet()
method inherited from it. Each time the web server receives a GET
request for this servlet, the server invokes this
doGet() method, passing it an
HttpServletRequest object and an
HttpServletResponse object.
The HttpServletRequest represents the client’s request. This object gives a servlet access to information ...