The @Target annotation in Spring Boot

The @Target annotation in Java is a meta-annotation that is used to specify the types of elements to which an annotation can be applied. It is part of the Java Annotation API and allows you to restrict the usage of your custom annotations to specific program elements like classes, methods, fields, etc. In this tutorial, we’ll explore the @Target annotation with simple examples.

Basic Syntax of @Target

The @Target annotation takes an array of ElementType constants as its value. Each constant represents a type of program element to which the annotation can be applied. The possible ElementType constants include:

• ElementType.ANNOTATION_TYPE: Annotation type declaration.
• ElementType.CONSTRUCTOR: Constructor declaration.
• ElementType.FIELD: Field declaration.
• ElementType.LOCAL_VARIABLE: Local variable declaration.
• ElementType.METHOD: Method declaration.
• ElementType.PACKAGE: Package declaration.
• ElementType.PARAMETER: Parameter declaration.
• ElementType.TYPE: Class, interface (including annotation type), or enum declaration.

Here’s an example of how to use @Target:

In this example, the @MyAnnotation annotation can only be applied to class/interface declarations (ElementType.TYPE) and method declarations (ElementType.METHOD).

Example: Creating a Custom Annotation with @Target

Let’s create a simple custom annotation called @MethodInfo and use @Target to specify where it can be applied.

In this example:

• The @MethodInfo annotation can only be applied to methods (ElementType.METHOD).
• The @Retention(RetentionPolicy.RUNTIME) annotation is included to indicate that the annotation information should be retained at runtime.

Now, let’s use the @MethodInfo annotation in a class:

Here, we’ve applied the @MethodInfo annotation to the myMethod method. The annotation specifies details such as the author, date, revision, and comments related to the method.

Conclusion

The @Target annotation is a powerful tool for custom annotation developers to specify where their annotations can be used within Java code. By using @Target, you can enforce constraints on the types of program elements to which your annotations can be applied, providing a more controlled and meaningful usage of your annotations. Understanding and utilizing @Target is essential for creating effective and well-designed custom annotations in Java.