Singleton VS ServletContext VS Inheritance

Question

I just poseted this in a reply to another thread, but I think it deservs its own.
I'm confused on how to implemente something like a database access between two servlets, say a Login Servlet and a Registration Servlet. Both need to access cuncurrently to the database using the same connection.
So three ways of doing this are with a Singleton Object, which handles database access. Sharing that same Object through the ServletContext and instead of having an object to handle database access, handle it in a Servlet which will then be inherited by both the Login a Registration Servlets...
I was looking for your opinion on which would be the best way to implement this...?

Answer 1

BalusC, I agree with you on all that. The thing is that I need to use a file...So I need the accesses to be handled concurrently..I do realy wish I could you a DB as it would save me all this trouble with concurrency on reads and writes...
Here is a piece of my code:
The object I'm using as a Singleton:
public class Users {
     private static Users ref;
     private static final String FILENAME = "users.xml";
     private static Hashtable users = new Hashtable();
     private ReadWriteLock lock = new ReentrantReadWriteLock();
     private static XMLDecoder dec;
     private static XMLEncoder enc;
     private static int id;
     private Users() {}
     public static synchronized Users getUsers()
          if(ref == null) {
               ref = new Users();
               try {
                    dec = new XMLDecoder(new BufferedInputStream(new FileInputStream(FILENAME)));
                    dec.close();
               catch(FileNotFoundException e) {
                    System.out.println("Vou criar um file novo");
                    try {
                         enc = new XMLEncoder(new BufferedOutputStream(new FileOutputStream(FILENAME)));
                         enc.writeObject(new Hashtable());
                         id = 0;
                         enc.writeObject(id);
                         enc.close();
                    } catch(Exception ex) {ex.printStackTrace();}
          return ref;
     public Object clone() throws CloneNotSupportedException
          throw new CloneNotSupportedException();
     public User findUser(String username)
          try {
               lock.readLock().lock();
               dec = new XMLDecoder(new BufferedInputStream(new FileInputStream(FILENAME)));
               users = (Hashtable) dec.readObject();
               dec.close();
               lock.readLock().unlock();
               return (User)users.get(username);
          } catch(Exception e) {
               System.out.println("There was a problem decoding XML");
               return null;
     public boolean saveUser(String username, String password)
          try {
               lock.readLock().lock();
               dec = new XMLDecoder(new BufferedInputStream(new FileInputStream(FILENAME)));
               users = (Hashtable) dec.readObject();
               id = (Integer)dec.readObject();
               dec.close();
               lock.readLock().unlock();
               User u = new User();
               u.setUsername(username);
               u.setPassword(password);
               u.setId(id+1);
               users.put(username, u);
               lock.writeLock().lock();
               enc = new XMLEncoder(new BufferedOutputStream(new FileOutputStream(FILENAME)));
               enc.writeObject(users);
               enc.writeObject(id+1);
               enc.close();
               lock.writeLock().unlock();
               System.out.println("save done");
               return true;
          } catch(Exception e) {
               System.out.println("There was a problem decoding XML [save fail]");
               System.out.println(e.getMessage());
               return false;
}And the Login servlet
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
          // TODO Auto-generated method stub
          String username = request.getParameter("login");
          String password = request.getParameter("pass");
          User usr = authenticate(username, password);
          if(usr != null)
               HttpSession session = request.getSession(true);
               session.setAttribute("user", usr);
               response.sendRedirect("Home");
          else
               response.setContentType("text/html");
             PrintWriter out = response.getWriter();
             out.println("<html>");
             out.println("<head>");
             out.println("<title>Hello World!</title>");
             out.println("</head>");
             out.println("<body>");
             out.println("<h2>El username/password no es valido!</h2>");
             out.println("<a href=\"Login\">Ententar otra vez!</a>");
             out.println("</body>");
             out.println("</html>");
     private User authenticate(String username, String password)
          Users tmp = Users.getUsers();
          User usr = tmp.findUser(username);
          if(usr != null)
               if(usr.getPassword().equals(password))
                    return usr;
          return null;
     }