Java注解（annotation）概述

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。

一般来说Annotation有如下三种使用情形：

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.

为编译器提供辅助信息 — Annotations可以为编译器提供而外信息，以便于检测错误，抑制警告等.

编译源代码时进行而外操作 — 软件工具可以通过处理Annotation信息来生成原代码，xml文件等等.

运行时处理 — 有一些annotation甚至可以在程序运行时被检测，使用.

参考资料：

https://www.race604.com/annotation-processing/

http://hannesdorfmann.com/annotation-processing/annotationprocessing101

http://blog.csdn.net/xfxyy_sxfancy/article/details/44275549#t3