Sahoo,
Thanks.
What happens when two things @Extract the same variable? Isn't this
setting what amounts to an global variable in the Habitat? Is there
an error produced, or does one variable just overwrite the other?
What if I ran two versions of a Service at the same time, or two
Services that both want to export a variable of the same class? From
what I understand, using an un-named @Extract seems to invite problems.
@Service public class BarImplA {
@Extract final MBeanServer mbeanServer = ...;
public BarImplA() {}
}
@Service public class BarImplB {
@Extract final MBeanServer mbeanServer = ...;
public BarImplB() {}
}
And of course I remain uneasy about @Inject thread safety, but
perhaps the implementation does something about.
Lloyd
On Jan 17, 2008, at 8:03 PM, Sahoo wrote:
> Lloyd L Chambers wrote:
>> Kosuke et al,
>>
>> [I think these comments/questions are relevant to other
>> developers...let's answer them, and I can help updating javadoc,
>> etc once I'm sure I understand it]
>>
>> I'm still learning annotations, so I don't "get" the javadoc for
>> @Extract and @Inject.
>>
>> Suggestion: there should be examples in the javadoc showing how to
>> use the annotations.
>>
>> For example, the Javadoc (https://hk2.dev.java.net/nonav/auto-
>> depends/apidocs/org/jvnet/hk2/annotations/Extract.html) doesn't
>> tell me anything really about how to use @Extract ("Annotation
>> marks instances of object which are labeled as exported by a
>> component"):
>>
>> 1. Exported to where?
> Exported to the component registry (a.k.a. Habitat in HK2).
>> 2. Under what name?
> Unless you specify a name in @Extract, it is an unnamed object.
>> What is the naming convention?
> Any string
>> 3. What do I write to @Inject it? What happens if it's not yet
>> available?
>>
> Let's take an example:
>
> @Service public class BarImpl implements PostConstruct {
> @Extract BazImpl baz;
> public BarImpl() {System.out.println("BarImpl()");}
> public void postConstruct() {baz = new BazImpl();}
> }
>
> public class BazImpl {
> public BazImpl() { System.out.println("BazImpl()");}
> }
>
> @Service public class Foo implements ModuleStartup {
> @Inject Habitat habitat;
> @Inject BarImpl bar;
>
> public void setStartupContext(StartupContext context) {}
>
> public void run() {
> System.out.println(bar.baz);
> System.out.println(habitat.getComponent(BazImpl.class));
> }
> }
>
> When you run it using mvn hk2:run, you shall see something like this:
> BarImpl()
> BazImpl()
> sahoo.hk2test4.BazImpl_at_b3319f
> sahoo.hk2test4.BazImpl_at_b3319f
>
> The point worth noting is that BazImpl() is called only once and
> habitat.getComponent(BazImpl.class) returned the same instance as
> pointed to by bar.baz.
>
> Note that, we need not mark BazImpl as a @Service, although in many
> cases it may itself be a service. I think there is some work to be
> in HK2 about @Extract processing, as it currently only exports the
> object under the type name of the implementation class (in this
> case BazImpl.class).
>
> Yes, we plan to add some examples to the documents soon.
> Thanks,
> Sahoo
>> ---
>> Lloyd L Chambers
>> lloyd.chambers_at_sun.com <mailto:lloyd.chambers_at_sun.com>
>> Sun Microsystems, Inc
>>
>>
>>
>
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---
Lloyd L Chambers
lloyd.chambers_at_sun.com
Sun Microsystems, Inc