Careeroza

Custom Annotations

Declaring an Annotation

Use @interface. Two meta-annotations decide how it behaves:

Meta-annotation	Values
`@Retention`	`SOURCE` (dropped by compiler, e.g. Lombok), `CLASS` (in .class, not at runtime — default), `RUNTIME` (readable with reflection)
`@Target`	`TYPE`, `METHOD`, `FIELD`, `PARAMETER`, `CONSTRUCTOR`, `RECORD_COMPONENT`...
`@Inherited`	subclasses inherit the class annotation
`@Repeatable`	allow the same annotation more than once
`@Documented`	include in Javadoc

Elements and Defaults

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface RateLimit {
    int requestsPerMinute() default 60;   // element with a default
    String key() default "ip";
}

// usage
@RateLimit(requestsPerMinute = 5, key = "userId")
public OtpResponse sendOtp(String phone) { ... }

// an annotation with a single element named value() can be written without the name
public @interface Role { String value(); }
@Role("ADMIN") void deleteUser(long id) { ... }

Note: Element types are limited to primitives, String, Class, enums, other annotations and arrays of these.