I think extraction will work or at least should... now the real
problem is later, with injection....
say you have
@Inject
MBeanServer foo;
which one are u supposed to get ?
Maybe we should force the @Extract to have name property (or use the
field name by default) so that extracted resources are always stored
in the habitat with a name.
With your example the second extraction would fail since there is
already a MBeanServer nammed mBeanServer in the habitat. Seems like
predictable behaviour.
comment ?
On Jan 18, 2008, at 11:58 AM, Lloyd L Chambers wrote:
> 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
>
>
>
>
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