[Springframework-developer] New bean instantiation "type"

[Andy D. <an...@ma...>]

=2D----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Hello,
  I posted a message to the Spring "help" forum, and it has become more of =
a=20
development idea.  I'd like to copy the two help forum messages here and=20
solicit feedback from Spring developers.  You will find the two messages=20
below.
  Thanks for your consideration.

=46irst message, posted 3/24/04:

<<<<<<<<<<<<

I have two questions regarding Spring's instantiation of beans that are not=
=20
singletons.
 First, let's say I have the following XML:
=20
 ----
 <beans>
 <bean id=3D"a" class=3D"A" singleton=3D"false">
 <property name=3D"b">
 <ref bean=3D"b"/>
 </property>
 </bean>
=20
 <bean id=3D"b" class=3D"B" singleton=3D"false">
 <property name=3D"c">
 <ref bean=3D"c"/>
 </property>
 </bean>
=20
 <bean id=3D"c" class=3D"C" singleton=3D"false">
 <property name=3D"a">
 <ref bean=3D"a"/>
 </property>
 </bean>
 </beans>
 ----
=20
 What will Spring do when I attempt to get "a"? Will this even work? How ma=
ny=20
times will each class be instantiated?
 The second question is similar to the first. Here is another config file:
=20
 ----
 <beans>
 <bean id=3D"a" class=3D"A" singleton=3D"false">
 <property name=3D"b">
 <ref bean=3D"b"/>
 </property>
=20
 <property name=3D"c">
 <ref bean=3D"c"/>
 </property>
 </bean>
=20
 <bean id=3D"b" class=3D"B" singleton=3D"false">
 <property name=3D"c">
 <ref bean=3D"c"/>
 </property>
 </bean>
=20
 <bean id=3D"c" class=3D"C" singleton=3D"false">
 </bean>
 </beans>
 ----
 When I attempt to get "a", how many times will "c" be instantiated? Once f=
or=20
each reference, or once for the entire getBean call?

<<<<<<<<<<<<<<<<<<<<<

I then decided to perform my own tests based on the two examples above.  He=
re=20
is my response:

<<<<<<<<<<<<<<<<<<<<<

Well, I've tested it, and my fears are confirmed. Everytime a non-singleton=
 is=20
referenced in the XML, it is re-instantiated. I haven't looked at Spring's=
=20
source code, but I'm guessing it is using getBean internally to get a bean=
=20
referenced in the XML. This means that the first example never returns. It =
is=20
either stuck in an infinite loop, or it is in infinite recursion, though=20
after a minute of running I didn't get a StackOverflow.
 The second example instantiates C twice, though it does return.
 What I need is the ability to have an object graph instantiated every time=
=20
getBean is called, though in that instantiation, referenced objects should=
=20
only be instantiated at most one time.
 Look at the second example. What we would like is the ability to have A, B=
,=20
and C instantiated every time getBean is called, but each class should be=20
instantiated at most once. In other words, the same C reference is passed t=
o=20
both A and B, though all these objects will be reinstantiated the next time=
=20
getBean is called. The behavior we are looking for would be exactly the sam=
e=20
as if all the beans were singletons, but we used a new XmlBeanFactory for=20
every call of getBean. Of course, this is a possible solution to our proble=
m,=20
but I'm guessing it would be terribly ineffecient.
 Right now there are two "types" of bean instantiation: singleton, and=20
non-singleton. Does anyone see value in creating a third type? This new typ=
e=20
would indicate, "create a new instance of the object for each getBean(...)=
=20
call, but never more than one instance, so that all references within the=20
scope of the getBean(...) call get the same instance on reference."=20
=2D----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)

iD8DBQFAYxvMdgQy3TUmt38RAtk+AJ4wC9epDPb5wnlBbnwsCmAuB5VVCgCffJ6t
fme2cmOWLhe/YUtegfx02LU=3D
=3DI6nb
=2D----END PGP SIGNATURE-----