A Servlet is a server side software
component written in Java and runs in a compatible container environment
known as a Servelt container (like Apache Tomcat). Servlets are
predominantly used in implementing web applications
that generate dynamic web pages. They can however generate any other
content type like XML, text, images, sound clips, PDF, Excel files
programmatically.
A Servlet written to generate some HTML may look like this:
public class MyServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter w = response.getWriter();
w.write(“<html>”);
w.write(“<body>”);
Date d = new Date();
w.write(d.toString());
w.write(“</body>”);
w.write(“</html>”);
}
}
The code above contains a mixture of
HTML and Java source code. Such is not very readable and maintainable.
JSP which stands for JavaServer Pages provides a better alternative. For
example, the following is a fragment of JSP code that results in
identical output:
<%@page import=”java.util.Date”%>
<html>
<body>
<%= new Date().toString() %>
</body>
</html>
Web page authors find JSP easier to
write and maintain. JSP files are however translated into Servlets by a
Servlet container at the time JSP files are first accessed. However, business logic writers find Servlets to be easier to work with.
A request received by a web application
should trigger the execution of some business logic and then generate a
resultant web page as the response. In modern day web applications,
controlling the overall request processing cycle is mostly handed by
Servlets. As the last stage in processing a request, such a Servlet
generally hands over the responsibility of generating the dynamic HTML
to a JSP.
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