<context:annotation-config> 用來注入已經在上下文注冊的bean，無論bean是定義在XML中還是被?package scanning。

<context:component-scan>僅scans packages 去注冊應用上線文中的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>

加載環(huán)境產生輸出：

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

這是正常的輸出，但是這是老的spring 風格.，現(xiàn)在我們使用注解。

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" />

加載結果：

creating bean B: com.xxx.B@5e5a50 creating bean C: com.xxx.C@54a328 creating bean A: com.yyy.A@a3d4cf

上面的結果并沒有完成注入，這是因為@Autowired 只是一個注解，如果讓它完成注入工作需要<context:annotation-config />

改變一下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" />

輸出結果：

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

現(xiàn)在，我們使用注解注釋Bean 刪除砸xml中的定義：

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 />

加載后什么都沒有輸出。

<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，得到了我們想要的結果。

?

總結：

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 />.

?

?

轉載于:https://www.cnblogs.com/codeingthink/p/9257604.html

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