Is this thread safe?

Question

I've got a HttpServletRequest instance variable in my servlet that I use in my model to retrieve parameters. The servlet looks like:
public class MyServlet extends HttpServlet implements Controller {
  HttpServletRequest req;
  public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    processRequest(req, resp);
  public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    processRequest(req, resp);
  public void processRequest(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    this.req = req;
    MyModel model = new MyModel(this);
    model.retrieve();
  public String getParameter(String parameter) {
    return req.getParameter(parameter);
}The Controller interface has only one method - public String getParameter(String parameter)
In MyModel because I pass an instance of Controller into the constructor I can do - controller.getParameter(parameter);
Is what I'm doing thread safe?

Answer 1

Actually, a static nested class is more appropriate than an inner class as there is no implicit outer-class reference to maintain:
public class MyServlet extends HttpServlet {
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        processRequest(req, resp);
    public void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        processRequest(req, resp);
    public void processRequest(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException {
        MyModel model = new MyModel(new MyController(req));
        model.retrieve();
    private static class MyController implements Controller {
        private HttpServletRequest req;
        MyController(HttpServletRequest req) {
            this.req = req;
        public String getParameter(String parameter) {
            return req.getParameter(parameter);
}This code is now thread safe because there is a different instance of MyController per thread. Note that if an instance of MyController is accessed by multiple threads, then its thread safety is dependent upon the thread safety of HttpServletRequest. However, based on the sort of thing I assume you are trying to do, I doubt you will be sharing instances between threads.