The annotation provides the ability to define one or many conditions on a bean.

Consider the following example:

Using @Requires

@Requires(beans = DataSource.class)
@Requires(property = "datasource.url")
class JdbcBookService implements BookService {

Using @Requires

The above bean defines two requirements. The first indicates that a DataSource bean must be present for the bean to load. The second requirement ensures that the datasource.url property is set before loading the bean.

If you have multiple requirements that you find you may need to repeat on multiple beans then you can define a meta-annotation with the requirements:

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PACKAGE, ElementType.TYPE})
@Requires(beans = DataSource.class)
@Requires(property = "datasource.url")
}

Using a @Requires meta-annotation

Using a @Requires meta-annotation

@Documented
@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.CLASS, AnnotationTarget.FILE)
@Requirements(Requires(beans = [DataSource::class]), Requires(property = "datasource.url"))

In the above example an annotation called RequiresJdbc is defined that can then be used on the instead:

If you have multiple beans that need to fulfill a given requirement before loading then you may want to consider a bean configuration group, as explained in the next section.