How to build a Java servlet
It is a small web application written in Java, running on the server and interacting with the remote client. It sends to the client data in HTML or another format.
The client can access it from the browser with a URL.
It runs in a special server, a servlet container.
Servlet container
It is a specialized web server and a runtime environment for servlets it contains, which provides the API of classes and methods they can use. There are examples of those classes below.
The best known is Apache Tomcat (different from the Apache server), which is also an HTTP server.
It is also known as web container or web engine. Besides Tomcat may be added Jetty, Geronimo, Winstone, Jaminid.
JBoss encapsulates Tomcat.
Example of a minimalist servlet
Hello World! displayed by a servlet:
package demo;
import java.io.*;
import javax.servlet.http.*;
import javax.servlet.*;
public class HelloServlet extends HttpServlet
{
public void doGet (HttpServletRequest req, HttpServletResponse res)
throws ServletException, IOException
{
PrintWriter out = res.getWriter();
out.println("Hello, world!");
out.close();
}
}
Get the Java source code.
Another example provided by Apple that creates a web page:
import java.io.*;
import java.text.*;
import java.util.*;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.naming.*;
import javax.rmi.*;
public class HelloWorldServlet extends HttpServlet
{
private HelloWorld hw = null;
public HelloWorldServlet() throws NamingException
{
Context ctx = new InitialContext();
HelloWorldHome home = (HelloWorldHome)
PortableRemoteObject.narrow(ctx.lookup("HelloWorld"),
HelloWorldHome.class);
try { this.hw = home.create(); } catch (Exception e) { }
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException, ServletException
{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head>");
out.println("<title>Demo</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Hello World!</h1>");
out.println(this.hw.hi());
out.println("</body>");
out.println("</html>");
}
}
Download the complete source code.
This servlet generates the following HTML page:
<html>
<head>
<title>Demo</title>
</head>
<body>
<h1>Hello World!</h1>
... content from the user...
</body>
</html>
Tools and resources: The site of Sun. Various downloads including the specification.