We usually in development, you can customize annotations, but also have the relevant code annotation processor implementation, in order to make notes complete the corresponding function after you have defined annotations. Because annotation functions just described function, annotation processor is executing code implementing logic functions to achieve the described annotations.
Like for example, xml configuration file description of the resource, is a static description, there is no ability to execute logic, there must be logic-related code to handle it describes.
The spring used annotations, annotation have their corresponding processor. Related reference as follows:
https://blog.csdn.net/m0_37664906/article/details/78873606