Andi Setiyadi wrote:
> I have a question about database connection.
> In the code below, what happen when one request has just creating a session
> for storing the connection, and the another request is about to execute
> session.removeAttribute that will kill the session? Is the session unique
> for each request, means that when one user kill connection session will not
> affect other user's connection session? Or all request share the same
> connection session?
> Is this a good way to maintain connection for each request? Why?
>
> Thank you. I appreciated any input.
>
> Andi Setiyadi
>
> Attached code:
>
> public void doGet(HttpServletRequest req, HttpServletResponse res) throws
> IOException, ServletException {
>
> HttpSession session = req.getSession(true);
> Connection conn;
>
> synchronized(session) {
> conn = (Connection) session.getAttribute("connection");
> if (conn == null) {
> ConnectionBean cBean = new ConnectionBean();
> conn = cBean.getConnection();
> session.setAttribute("connection", conn);
> }
> }
>
> // perform some tasks
> ...
>
> try {
> if (conn != null) {
> conn.close();
> }
> }
>
> catch(Exception e) { }
>
> session.removeAttribute("connection");
> }
> [...]
Hi :-) just IMHO, because a HttpSession is a "identify" of a connection
between a browser and a "Servlet Container+webapp+...?" within a period
of time, so if different client uses different browser (not different browser
instance) to access your Servlet class, I think the Servlet container will
make/keep
different insatnce of HttpSession, i.e., req.getSession(true) will return
different
session, I just made a test with TOMCAT4.0b1(standalone, J2SE1.3, winnt40),
I use IE5.0 and NN4.7 in my computer to visit MyServlet, and I got different
hashCode() of two sessions.
and I guess perhaps it is better to maintain DBConnection with a
DBConnectionPool, for example :
* make a SingleTon-style DBConnectionPool, let its class be loaded by
a classloader which is "upper" webapp classloader(for example, put its
class in TOMCAT_HOME/lib) if I use TOMCAT, and in init() or
somewhere else, I "init" it, and got a onlyone instance.
* directly use the static refrence within its class to use that onlyone
instance of DBConnectionPool, or put that instance in ServletContext
so we can get a refrence of it later.
* we can put all the "synchronized operation" within DBConnectionPool
itsself, i.e.
- we can use "this" of DBConnectionPool to lock code because of
it is SingleTon-style
- or use this.getClass() to lock code, because we load it with a classloader
which will not be destroyed.
* if I Don't put the "synchronized operation" within DBConnectionPool itsself,
we also can use some "wide area onlyone thing within container" to lock the
code, for example (in TC4.0bx):
- this.getServletContext()
- this.getServletContext().getClass()
- this.getServletContext().getClass().getClassLoader()
- session.getClass()
- session.getClass().getClassLoader()
- ...
Bo
Apr.27, 2001
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