[cdi-dev] [JBoss JIRA] (CDI-535) cdi instance injection ordering

Ochieng Marembo (JIRA) issues at jboss.org
Wed Oct 5 02:38:00 EDT 2016

    [ https://issues.jboss.org/browse/CDI-535?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13302666#comment-13302666 ] 

Ochieng Marembo commented on CDI-535:

I think using the ```@OrderBy``` qualifier would be more suited to situations where you have no control of all possible interface implementations.

Depending on when the OrderBy is executed, it could be called the first time the instance list is actually requested for iteration, hence delaying instantiating expensive implementationd.

Strictly the OrderBy cannot be a normal qualifier as it will force all instances to be so qualified, which for purposes of considering 3rd party implementations, would simply not work.

We could  have as an implicit qualifier.

> cdi instance injection ordering
> -------------------------------
>                 Key: CDI-535
>                 URL: https://issues.jboss.org/browse/CDI-535
>             Project: CDI Specification Issues
>          Issue Type: Feature Request
>          Components: Beans
>    Affects Versions: 2.0 (discussion)
>            Reporter: Ochieng Marembo
>            Priority: Optional
> We should allow ordering of bean instance injection using the ```Instance<MyBeanInterface>``` when an instance injection is used.
> h3. Use case:
> Developer always define a kind of chain of processor beans, which may need to run in specific order.
> h3. Current scenario:
> Using the Instance injection mechanism, a developer can inject multiple beans implementing the same interface and iterate of them. In order to ensure ordering, the developer could do one of the following:
> #1
> {code}
> private Iterable<MyBeanInterface> myBeans;
> @Inject
> void injectBeans(@Any Instance<MyBeanInterface> myBeans) {
>   //the create order does some kind of ordering on the beans.
>    this.myBeans = createOrder(myBeans);
> }
> {code}
> #2
> This second option may be expensive if we have to order the beans everytime we execute the logic, and if this bean is applicationscoped, it wont make sense to do the ordering in the method call.
> {code}
> @Any
> @Inject
> private Instance<MyBeanInterface> myBeans;
> public void doSomething() {
>   Iterable<MyBeanInterface> orderedbeans = createOrder(myBeans.select(someQualifier));
> }
> {code}
> h3. Our Proposal
> We already have {code}javax.annotation.Priority{code} or any cdi specific annotation which we can add to {code}MyBeanInterfaceImpl{code} so that on injection of an {code}Instance<MyBeanInterface>{code}, all possible injection values are sorted based on the {code}Priority.value(){code} and if no annotation is defined, defaults to {code}Priority.value = Integer.MAX_VALUE{code}
> {code}
> public interface MyBeanInterface {}
> @MyQualifier
> @Priority(0)
> public class MyFirstBean implements MyBeanInterface{
> }
> @MyQualifier
> @Priority(2)
> public class MySecondBean implements MyBeanInterface{
> }
> @ApplicationScoped
> public class MyBeanProcessor {
>   //We expect that this injected instances shall be in order based on the @Priority annotation
>   @Any
>   @Inject
>   private Instance<MyBeanInterface> myBeans;
> }
> {code}

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