import java.io.*; import java.util.*; import javax.servlet.*; import javax.servlet.http.*; // This simple class demonstrates how data can be communicated // between separate threads using context and configuaration objects. public class counter extends HttpServlet implements SingleThreadModel { // To be able to access the configuaration outside of init, we // store it as a state variable. ServletConfig storedConfig; // init is called when the web container calls the servlet for // the first time. Here, we use it to read an initial count from // the web.xml container and store it as a shared resource. public void init(ServletConfig config) { // Get the value corresponding to the initial count from the // web.xml file. String initCount = config.getInitParameter("InitialCount"); // We then store that name value pair as an attibute in the // servlet context, which in turn is part of the overall // servlet configuration. We then store the configuration // in the state variable. ServletContext context = config.getServletContext(); context.setAttribute("count", initCount); storedConfig = config; } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // When a request is posted to the servlet, we retrieve the current // context from the stored configuaration state variable, and then // retrieve the count from that context. ServletContext context = storedConfig.getServletContext(); int count = Integer.parseInt((String)context.getAttribute("count")); // We then increment the count, and store it back into the context // which is still stored in the configuration. count = count + 1; context.setAttribute("count", ""+count); PrintWriter out = response.getWriter(); // Finally, we write the count into a web page to send as the response. out.println("

Your ID number is "); out.println("" + count + "."); out.println("

"); } }