Well, google for "singletons considered harmful" and reserve a couple of
hours for reading...
Here's one that explains it pretty well:
http://tech.puredanger.com/2007/07/03/pattern-hate-singleton
Olle Hallin
Senior Java Developer and Architect
olle.hal...@crisp.se
www.crisp.se
2009/10/13 Argo Vilberg <wilps...@gmail.com>
> anti-pattern?
>
> why it makes testing much harder?
>
> I use singleton for my own connection pooling and cache and cluster system.
> All works very fine!
>
> 2009/10/13 Olle Hallin <olle.hal...@hit.se>
>
> > Singletons is an anti-pattern that the Java community abandoned years
> ago!
> > The main reason is that it makes testing much harder.
> >
> > Besides, your example is wrong. The constructor must be private, or else
> > the
> > singleton is broken.
> >
> > Olle Hallin
> > Senior Java Developer and Architect
> > olle.hal...@crisp.se
> > www.crisp.se
> >
> >
> >
> >
> > 2009/10/13 Argo Vilberg <wilps...@gmail.com>
> >
> > > very simple solution is creata Singleton java class.
> > >
> > >
> > > public class MallBean{
> > > public final static MallBean INSTANCE = new MallBean();
> > >
> > > public MallBean() {
> > > }
> > >
> > > ....
> > >
> > > }
> > >
> > >
> > > And access
> > >
> > > MallBean.INSTANCE.getSomething.
> > >
> > >
> > > And if you first time calling this, class is created and only ONE this
> > type
> > > of class can be created.
> > > And this class is accessible everyone.
> > >
> > >
> > > Enjoy!
> > >
> > > Argo
> > >
> > >
> > > 2009/10/13 TomMax <tryk...@poczta.onet.pl>
> > >
> > > >
> > > > Hi all,
> > > >
> > > > I'm working in a developers team with Tapestry applications (version
> > > 4.0.2)
> > > > for more than 2 years. Our Tapestry applications works on various
> > > > Application Servers (JBoss, SAP Netweaver), and usually we were able
> in
> > > our
> > > > team to resolve all problems, recently however, we spotted a problem
> > with
> > > > Application State Object, which is responsible for user session data
> > and
> > > we
> > > > can't find the bug.
> > > >
> > > > The problem is that two users see sometimes the same data on a page.
> In
> > > our
> > > > scenario User1 and User2 have their own userSession objects (they are
> > ASO
> > > > object with session scope), these objects keep all their data, and
> > these
> > > > objects are injected to every page in .page file:
> > > >
> > > > <inject property="userSession" object="userSession" type="state" />
> > > >
> > > > Every user has own userSession object, so every user should see only
> > his
> > > > own
> > > > data on a page, but sometimes (quite rarely), we got the situation,
> > that
> > > > User2 sees the data from User1 userSession object when he get the
> page,
> > > > where User1 was earlier.
> > > > So far I know, in case of ASO objects, the references in a page to
> > these
> > > > objects, should be set to null on pageDetach action. So each time
> when
> > > the
> > > > user is receiving the page from PagePool (or newly created page), he
> > > should
> > > > obtain also fresh ASO object from ApplicationStateManager.
> > > > We have got currently this problem not so often (usually it is one or
> > two
> > > > times in a two week period, in case when the application is used by
> 3-4
> > > > persons 8 hours per day), and when the problem happens, usually all
> > > working
> > > > users are receiving wrong data (they see the data from other users).
> > > >
> > > > I hope someone will be able to help me.
> > > >
> > > > Thanks
> > > > Tomek
> > > >
> > > >
> > > > --
> > > > View this message in context:
> > > >
> > >
> >
> http://www.nabble.com/-T4--Two-users-see-the-same-data---problem-with-ASO-objects-tp25872478p25872478.html
> > > > Sent from the Tapestry - User mailing list archive at Nabble.com.
> > > >
> > > >
> > > > ---------------------------------------------------------------------
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> > > > For additional commands, e-mail: users-h...@tapestry.apache.org
> > > >
> > > >
> > >
> >
>
