CODEWITHSUNDEEP
javaspringannotations
membersound
membersound

Reputation: 86657

How to combine multiple annotations to single one?

I have two annotations from a framework. Often I use those two annotations both on the same field. Thus I'm trying to create a "combined" annotation that contains that both two.

But I don't know if it is possible at all:

The existing annotations (that I have no control of):

@Target({ElementType.PARAMETER, ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface ApiParam {
    String name() default "";
}

@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
public @interface ApiModelProperty {
    String name() default "";
}

My Custom annotation that I'm trying to create:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
@ApiParam
@ApiModelProperty
public @interface SwaggerParam {
     String name() default "";
}

Result: the annotations are not applicable to annotation type.

Question: Is there any chance?

Upvotes: 11

Views: 9559

Answers (2)

Stefan Feuerhahn
Stefan Feuerhahn

Reputation: 1794

Composing annotations like you did can only be done if your framework supports scanning for meta-annotations. Thus the framework not only has to scan for direct annotations but also for an annotation's meta-annotations recursively.

Multiple frameworks support this, some of which are:

Upvotes: 2

Plog
Plog

Reputation: 9622

Unfortunately you can't do this since it is not possible to extend annotations.

Is there something like Annotation Inheritance in java?

When I first answered this I was initially confused by the Spring framework approach to this shortcoming whereby they use meta level annotations (such as @Component as a meta annotation for @Controller/@Configuration etc.) as a sort of workaround.

See: https://docs.spring.io/spring/docs/3.2.x/spring-framework-reference/html/beans.html#beans-annotation-config

Upvotes: 5

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