A qualifier is an annotation that has @Qualifier declared on it, which signifies to the container that this qualifier annotation can be utilized on injection points and beans to distinguish different implementations of the same bean type.
A qualifier annotation, without any members, is just:
@Qualifier
@Retention(RUNTIME)
@Target( { TYPE, METHOD, FIELD, PARAMETER } )
public @interface MyQualifier {}We can use field injection with @MyQualifier by:
@Inject @MyQualifier private Locale myLocale;
Or constructor injection:
@Inject
public Notifications(@MyQualifier Locale myLocale) {
this.myLocale = myLocale;
}Or an initializer method:
@Inject
public void setLocale(@MyQualifier Locale myLocale {
this.myLocale = myLocale;
}Lastly, producing a Locale with the @MyQualifier annotation to match the injection points:
@Produces
@MyQualifier
public Locale getMyLocale() {
return Locale.US;
}