Counting with Globals

• Actually, each registered name of a servlet is associated with one instance of the servlet.
• All instances have, of course, access to the same static variables (right?).
• So we could count all the instances with:

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

public class HolisticCounter 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 {
    res.setContentType("text/plain");
    PrintWriter out = res.getWriter();

    count++;
    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.");

    classCount++;
    out.println("Across all instances, this servlet class has been " +
                "accessed " + classCount + " times.");
  }
}