about annotations

来源 ：http://www.jroller.com/habuma/date/20070516
spring 2.0 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:aop="http://www.springframework.org/schema/aop"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
            http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
          http://www.springframework.org/schema/aop 
            http://www.springframework.org/schema/aop/spring-aop-2.0.xsd">
          
  <bean id="quest"
      class="com.springinaction.chapter01.knight.HolyGrailQuest"/>

  <bean id="knight"
      class="com.springinaction.chapter01.knight.KnightOfTheRoundTable">
    <constructor-arg value="Bedivere" />

    <property name="quest" ref="quest" />
  </bean>

  <bean id="minstrel"
      class="com.springinaction.chapter01.knight.Minstrel"/>

  <aop:config>
    <aop:aspect ref="minstrel">

      <aop:pointcut
          id="questPointcut"
          expression="execution(* *.embarkOnQuest(..)) and target(bean)" />

      <aop:before
          method="singBefore"
          pointcut-ref="questPointcut" 
          arg-names="bean" />

      <aop:after-returning
          method="singAfter"
          pointcut-ref="questPointcut" 
          arg-names="bean" />
    </aop:aspect>
  </aop:config>

</beans>

<?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:aop="http://www.springframework.org/schema/aop"
       xmlns:context="http://www.springframework.org/schema/context"

       xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
           http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-2.1.xsd">

  <context:component-scan
      base-package="com.springinaction.chapter01.knight" />

</beans>
<context:component-scan> is a new configuration element in the "context" namespace (which, BTW, is also new in Spring 2.1). This modest little element tells Spring to scan the "com.springinaction.chapter01.knight" package (as specified by the base-package attribute) and any subpackage looking for classes that might be annotated with @Component (new in Spring 2.1), @Repository (new in Spring 2.0), or @Aspect (provided by @AspectJ). If it finds any such class, it automatically will register the class as a bean in the Spring application context. So, although <context:component-scan> takes up so very little space in the XML configuration, it could be responsible for configuring dozens, hundreds, or even thousands of beans in Spring.
@Component tells Spring that this class should be automatically registered in the Spring context. By default, the class name is used as the bean's ID, but here I've explicitly specified that the bean should have an ID of "knight".

 @Autowired
  private Quest quest;

Next, notice that the setQuest() method is annotated with @Autowired. This tells Spring that this setter shold automatically be wired with a bean reference. The autowiring is "byType", so there will need to be a Quest bean in the Spring context. There's not one there now, but I'll add one soon.

package com.springinaction.chapter01.knight;

import org.springframework.stereotype.Component;

@Component
public class HolyGrailQuest implements Quest {
  public void embark() {
    System.out.println("Embarking on the quest for the Holy Grail!");
  }
}
 @Resource(name="grailQuest")
  public void setQuest(Quest quest) {
    this.quest = quest;
  }