Annotation 和Spring Annotation 知识整理

话题很大，感觉能力有限，很难把这些东西一次说透，只能稍作一个整理，供参考了。Annotation , 注解。可以粗浅理解是一种方法，这种方法能够帮助我们简化代码或者资源配置文件，提高工作效率。越来越多的框架提供Annotation拓展，帮助我们更好完成任务。

学习中的日用而不知现象：哪怕是一个java 的出学者，都回接触java annotation的，@Override 估计不陌生，@Override 告诉编辑器覆写父类方法，如果不小心hashCode写成hoshcode这个时候IDE会提示错误的；读代码的人也很清楚这个方法覆盖父类的方法。

package org.origin100.example.annotation;public class OverrideExample {private String field;private String attribute;@Overridepublic int hashCode() {return field.hashCode() + attribute.hashCode();}@Overridepublic String toString() {return field + " " + attribute;}
}

Spring中注解一览：

org.springframework.web.bind.annotation

Interface Hierarchyorg.springframework.web.bind.annotation.ValueConstants
Annotation Type Hierarchyorg.springframework.web.bind.annotation.RequestMapping (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.ResponseBody (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.PathVariable (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.SessionAttributes (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.RequestParam (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.RequestBody (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.ResponseStatus (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.ModelAttribute (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.InitBinder (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.ExceptionHandler (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.CookieValue (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.Mapping (implements java.lang.annotation.Annotation)
org.springframework.web.bind.annotation.RequestHeader (implements java.lang.annotation.Annotation)
Enum Hierarchyjava.lang.Object
java.lang.Enum<E> (implements java.lang.Comparable<T>, java.io.Serializable)
org.springframework.web.bind.annotation.RequestMethod

Hierarchy For Package org.springframework.stereotype

Annotation Type Hierarchyorg.springframework.stereotype.Component (implements java.lang.annotation.Annotation)
org.springframework.stereotype.Service (implements java.lang.annotation.Annotation)
org.springframework.stereotype.Repository (implements java.lang.annotation.Annotation)
org.springframework.stereotype.Controller (implements java.lang.annotation.Annotation)

可以看出都实现了java.lang中的Annotation。它们的用法可以参见《详解Spring 3.0基于Annotation的依赖注入实现》。看看官方文档的代码片

org.springframework.samples.petclinic.web

@Controller
public class HelloWorldController {@RequestMapping("/helloWorld")public ModelAndView helloWorld() {ModelAndView mav = new ModelAndView();mav.setViewName("helloWorld");mav.addObject("message", "Hello World!");return mav;}
}

配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsdhttp://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd"><context:component-scan base-package="org.springframework.samples.petclinic.web"/>// ...</beans>

编译的时候自动会根据componet-scan 配置扫描相应的package根据@xxx类型生产相应的bean 或者注入方法。建议大家多看官方文档，文档之外任何解释都有点多余。

参考文章列表：

http://www.ibm.com/developerworks/cn/opensource/os-cn-spring-iocannt/index.html

http://static.springsource.org/spring/docs/3.0.x/reference/mvc.html#mvc-annotation-driven