Confuse in Chapter 25 Persistence in the Web Tier's example book store.

Question

Hi all,
I'm confusing about the example in Chapter 25 Persistence in the Web Tier.
the book store example creates the bookdbao in contextlistener
BookDBAO bookDBAO = new BookDBAO(emf);
context.setAttribute("bookDBAO", bookDBAO);and the bookdbao's constructor like this.
    public BookDBAO(EntityManagerFactory emf) throws Exception {
        try {
            em = emf.createEntityManager();
        } catch (Exception ex) {
            throw new Exception(
                    "Couldn't open connection to database: " + ex.getMessage());
    }and the servler get bookdbao like
BookDBAO bookDBAO = (BookDBAO) getServletContext().getAttribute("bookDBAO");so if many users access the servlet at the sametime,
they all get the same bookDBAO,
but i think em is not guaranteed to be threadsafe.
so the example is not thread-safe, is it?
thanks

Answer 1

Hi all,
I'm confusing about the example in Chapter 25 Persistence in the Web Tier.
the book store example creates the bookdbao in contextlistener
BookDBAO bookDBAO = new BookDBAO(emf);
context.setAttribute("bookDBAO", bookDBAO);and the bookdbao's constructor like this.
    public BookDBAO(EntityManagerFactory emf) throws Exception {
        try {
            em = emf.createEntityManager();
        } catch (Exception ex) {
            throw new Exception(
                    "Couldn't open connection to database: " + ex.getMessage());
    }and the servler get bookdbao like
BookDBAO bookDBAO = (BookDBAO) getServletContext().getAttribute("bookDBAO");so if many users access the servlet at the sametime,
they all get the same bookDBAO,
but i think em is not guaranteed to be threadsafe.
so the example is not thread-safe, is it?
thanks