<context:annotation-config> 用来注入已经在上下文注册的bean，无论bean是定义在XML中还是被 package scanning。
<context:component-scan>仅scans packages 去注册应用上线文中的Bean。
example：
Lets start with a basic setup of three beans of type A, B and C, with B and C being injected into A.
package com.xxx; public class B {public B() {System.out.println("creating bean B: " + this);} }package com.xxx; public class C {public C() {System.out.println("creating bean C: " + this);} }package com.yyy; import com.xxx.B; import com.xxx.C; public class A { private B bbb;private C ccc;public A() {System.out.println("creating bean A: " + this);}public void setBbb(B bbb) {System.out.println("setting A.bbb with " + bbb);this.bbb = bbb;}public void setCcc(C ccc) {System.out.println("setting A.ccc with " + ccc);this.ccc = ccc; } }
XML配置：
<bean id="bBean" class="com.xxx.B" /> <bean id="cBean" class="com.xxx.C" /> <bean id="aBean" class="com.yyy.A"><property name="bbb" ref="bBean" /><property name="ccc" ref="cBean" /> </bean>
加载环境产生输出：
creating bean B: com.xxx.B@c2ff5
creating bean C: com.xxx.C@1e8a1f6
creating bean A: com.yyy.A@1e152c5
setting A.bbb with com.xxx.B@c2ff5
setting A.ccc with com.xxx.C@1e8a1f6 这是正常的输出，但是这是老的spring 风格.，现在我们使用注解。
First, lets autowire the bbb and ccc properties on bean A like so:
package com.yyy; import org.springframework.beans.factory.annotation.Autowired; import com.xxx.B; import com.xxx.C; public class A { private B bbb;private C ccc;public A() {System.out.println("creating bean A: " + this);}@Autowiredpublic void setBbb(B bbb) {System.out.println("setting A.bbb with " + bbb);this.bbb = bbb;}@Autowiredpublic void setCcc(C ccc) {System.out.println("setting A.ccc with " + ccc);this.ccc = ccc;} }
XML配置：
<bean id="bBean" class="com.xxx.B" /> <bean id="cBean" class="com.xxx.C" /> <bean id="aBean" class="com.yyy.A" />加载结果：
creating bean B: com.xxx.B@5e5a50
creating bean C: com.xxx.C@54a328
creating bean A: com.yyy.A@a3d4cf 上面的结果并没有完成注入，这是因为@Autowired 只是一个注解，如果让它完成注入工作需要<context:annotation-config />
改变一下XML的配置：
<context:annotation-config /> <bean id="bBean" class="com.xxx.B" /> <bean id="cBean" class="com.xxx.C" /> <bean id="aBean" class="com.yyy.A" />
输出结果：
creating bean B: com.xxx.B@15663a2
creating bean C: com.xxx.C@cd5f8b
creating bean A: com.yyy.A@157aa53
setting A.bbb with com.xxx.B@15663a2
setting A.ccc with com.xxx.C@cd5f8b 现在，我们使用注解注释Bean 删除砸xml中的定义：
package com.xxx; import org.springframework.stereotype.Component; @Component public class B {public B() {System.out.println("creating bean B: " + this);} }package com.xxx; import org.springframework.stereotype.Component; @Component public class C {public C() {System.out.println("creating bean C: " + this);} }package com.yyy; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import com.xxx.B; import com.xxx.C; @Component public class A { private B bbb;private C ccc;public A() {System.out.println("creating bean A: " + this);}@Autowiredpublic void setBbb(B bbb) {System.out.println("setting A.bbb with " + bbb);this.bbb = bbb;}@Autowiredpublic void setCcc(C ccc) {System.out.println("setting A.ccc with " + ccc);this.ccc = ccc;} }
xml中的配置：
<context:annotation-config />
加载后什么都没有输出。
<context:component-scan base-package="com.xxx" /> <context:annotation-config /> <context:component-scan base-package="com.xxx" /> <bean id="aBean" class="com.yyy.A" />
OK，得到了我们想要的结果。
总结：
The difference between the two is really simple!.
<context:annotation-config />Enables you to use annotations that are restricted to wiring up properties and constructors only of beans!.
Where as
<context:component-scan base-package="org.package"/>Enables everything that <context:annotation-config /> can do, with addition of using stereotypes eg.. @Component, @Service , @Repository. So you can wire entire beans and not just restricted to constructors or properties!.
<context:annotation-config>: Scanning and activating annotations for already registered beans in spring config xml.
<context:component-scan>: Bean registration + <context:annotation-config>
@Autowired and @Required are targets property level so bean should register in spring IOC before use these annotations. To enable these annotations either have to register respective beans or include <context:annotation-config />. i.e. <context:annotation-config /> works with registered beans only.
@Required enables RequiredAnnotationBeanPostProcessor processing tool
@Autowired enables AutowiredAnnotationBeanPostProcessor processing tool
Note: Annotation itself nothing to do, we need a Processing Tool, which is a class underneath, responsible for the core process.
@Repository, @Service and @Controller are @Component, and they targets class level.
<context:component-scan> it scans the package and find and register the beans, and it includes the work done by <context:annotation-config />.
