INTERACTIVE WEB SERVICES WITH JAVA

Introduction

Servlets are written in pure Java using the Servlet API:

like CGI scripts, Servlets follow the request-response pattern from HTTP
the API provides full access to the HTTP protocol
divided into two layers: generic and HTTP-specific

"Hello World" in Servlets:
import java.io.*; import javax.servlet.*; import javax.servlet.http.*; public class HelloWorld extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); out.println("<html><head><title>Servlet</title></head>"); out.println("<body><h1>Hello World!</h1>"); out.println("This page was last updated: " + new java.util.Date()); out.println("</body></html>"); } }

a servlet is a sub-class of HttpServlet
the doGet method defines the request handler for GET requests
the HttpServletRequest object contains all information about the request
the HttpServletResponse object is used for generating the response
a server makes only one instance of each Servlet class, but runs many threads

Useful methods in HttpServlet to be implemented in sub-classes:

void init()
void doGet(HttpServletRequest,HttpServletResponse)
void doPost(HttpServletRequest,HttpServletResponse)
String getServletName(), String getServletInfo()
void destroy()

Useful predefined methods:

void log(String), void log(String,Throwable)
ServletConfig getServletConfig() - reads server configuration for this Servlet
ServletContext getServletContext() - explained later...

Exceptions: ServletException