I am having some problems understanding the concept of component
instanciation. I read
http://felix.apache.org/documentation/subprojects/apache-felix-ipojo/apache-felix-ipojo-userguide/apache-felix-ipojo-instances.html
and I get the analogy to classes and objects but I still have some
concrete problems and some conceptual problems that I hope someone can
clarify
I thought I needed to create instances via iPOJO (@Instantiate or
factories) only for service providers since they never use new because the
impl is always hidden. However, I have some consumers @Component that I
instanciate myself (say in a main() method where I call new on them
directly). I made them @Component because they need to have things
injected. I was assuming that the ipojo bytecode manipulation would make
it so that when the objects were constructed, they would have their
dependencies injected (I'm using mostly method injection with @Bind) but
it seems that is not the case. Can someone clarify this for me please. Now
it seems to me that for iPOJO to do any injection at all I need to always
use one of the iPOJO instantiation techniques. The problem I have is that
then the constructors I made in the consumer classes are not called
This is a simplified example to illustrate my confusion
@Component(name="test")
public class MyFoo {
private List<External> externals; //injected
private Bar bar; //passed via constructor
public MyFoo(Bar otherBar) {
bar = otherBar;
externals = new ArrayList();
}
@Bind(aggregate=true)
public addExternal(External service) {
externals.add(service);
}
}
So, as can be seen here, I need to have all the providers of interface
External, but I also need a Bar object that I pass when I construct the
object using new MyFoo(someBar)
My problem is that if I need to pass a Bar to the constructor then I need
to use new; but If i use new, iPojo never invokes my injection method. On
the other hand, if I use iPOJOs instantiation (say I add @Instantiate)
then the injection does happen but it throws a NPE because the list has
not been created yet + bar will not be set. I know I can create the list
inside the injection method, but my question is more conceptual.
1) How are you supposed to accomplish this (making sure that the
constructor is invoked)?
2) How can iPOJO be calling addExternal (which means the object has been
created) without calling my one and only constructor that creates the
object? this is very counter-intuitive in standard java
3) Are you just not supposed to use constructors when using iPOJO
components maybe?
Thanks for any help
Alejandro Endo | Software Designer/Concepteur de logiciels
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