Annotation

Design pattern

Annotations are an implementation of the decorator design pattern.

The decorator pattern is a design pattern that allows behavior to be added to an individual object, dynamically, without affecting the behavior of other objects from the same class.

Annotations in Java

Annotations, a form of metadata, provide data about a program that is not part of the program itself. Annotations have no direct effect on the operation of the code they annotate.

Annotations have a number of uses:

• Information for the compiler: Annotations can be used by the compiler to detect errors or suppress warnings
• Compile-time and deployment-time processing: Software tools can process annotation information to generate code, XML files, and so forth.
• Runtime processing:  Some annotations are available to be examined at runtime.

Annotations in Spring

Spring uses annotations extensively as a core feature, especially Spring AOP, and almost all the functions we use in Spring rely on Spring annotations.

Essentially, it is a way for adding behavior to existing code without modifying that code.

reference:

https://en.wikipedia.org/wiki/Decorator_pattern

https://docs.oracle.com/javase/tutorial/java/annotations/

https://www.baeldung.com/spring-aop-annotation

https://github.com/hollischuang/toBeTopJavaer