Servlet Static Field As Counter : Counter « Servlet « Java Tutorial

import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;

public class MyServlet extends HttpServlet {

  static int classCount = 0;  // shared by all instances
  int count = 0;              // separate for each servlet
  static Hashtable instances = new Hashtable();  // also shared

  public void doGet(HttpServletRequest req, HttpServletResponse res)
                               throws ServletException, IOException {
    PrintWriter out = res.getWriter();

    out.println("Since loading, this servlet instance has been accessed " + count + " times.");

    // Keep track of the instance count by putting a reference to this
    // instance in a Hashtable. Duplicate entries are ignored.
    // The size() method returns the number of unique instances stored.
    instances.put(this, this);
    out.println("There are currently " +instances.size() + " instances.");

    out.println("Across all instances, this servlet class has been " +
                "accessed " + classCount + " times.");
<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"

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25.6.1.Servlet Static Field As Counter
25.6.2.Servlet Simple Counter