<context:annotation-config>
和 <context:component-scan>
是Spring Core里面的两个基础概念,每个使用者都有必要理解怎么使用它们以及这两个概念之间的区别。
annotation-config : Annotation config 的主要任务是激活注解。关键点是仍然需要注册bean。
component-scan : Component scan 能做任何annotaton config 能做的事情, 额外的还能够通过@Component
, @Service
,@Repository
etc 这些注解注册java bean。
还是来看代码比较直观:
SuperUser.java:
package com.lotusmedia.typesuper;
import com.lotusmedia.typenormal.NormalUser;
import com.lotusmedia.typenormal.TempUser;
public class SuperUser {
private NormalUser normalUser;
private TempUser tempUser;
public SuperUser(){
System.out.println("Super User Created ->"+this);
}
public void setNormalUser(NormalUser normalUser) {
System.out.println("Setting Normal User ->"+normalUser);
this.normalUser = normalUser;
}
public void setTempUser(TempUser tempUser) {
System.out.println("Setting Temp User ->"+tempUser);
this.tempUser = tempUser;
}
}
NormalUser.java :
package com.lotusmedia.typenormal;
public class NormalUser {
public NormalUser(){
System.out.println("Normal User Created->"+this);
}
}
TempUser.java :
package com.lotusmedia.typenormal;
public class TempUser {
public TempUser(){
System.out.println("Temporary User Created->"+this);
}
}
applicationContext.xml
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
">
<bean id="normalUser" class="com.lotusmedia.typenormal.NormalUser"></bean>
<bean id="tempUser" class="com.lotusmedia.typenormal.TempUser"></bean>
<bean id="superUser" class="com.lotusmedia.typesuper.SuperUser">
<property name="normalUser" ref="normalUser"></property>
<property name="tempUser" ref="tempUser"></property>
</bean>
</beans>
Executor.java :
package com.lotusmedia.run;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Executor {
public static void main(String args[]){
ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
}
}
执行程序,我们可以看到我们期望的输出如下:
Normal User Created->com.lotusmedia.typenormal.NormalUser@75e845c2
Temporary User Created->com.lotusmedia.typenormal.TempUser@1cec6b00
Super User Created ->com.lotusmedia.typesuper.SuperUser@6564dbd5
Setting Normal User ->com.lotusmedia.typenormal.NormalUser@75e845c2
Setting Temp User ->com.lotusmedia.typenormal.TempUser@1cec6b00
接下去我们采用最小替换法来观察并理解这里的变化。
package com.lotusmedia.typesuper;
import org.springframework.beans.factory.annotation.Autowired;
import com.lotusmedia.typenormal.NormalUser;
import com.lotusmedia.typenormal.TempUser;
public class SuperUser {
private NormalUser normalUser;
private TempUser tempUser;
public SuperUser(){
System.out.println("Super User Created ->"+this);
}
@Autowired
public void setNormalUser(NormalUser normalUser) {
System.out.println("Setting Normal User ->"+normalUser);
this.normalUser = normalUser;
}
@Autowired
public void setTempUser(TempUser tempUser) {
System.out.println("Setting Temp User ->"+tempUser);
this.tempUser = tempUser;
}
}
在配置文件里,我们移除属性的注入:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
">
<bean id="normalUser" class="com.lotusmedia.typenormal.NormalUser"></bean>
<bean id="tempUser" class="com.lotusmedia.typenormal.TempUser"></bean>
<bean id="superUser" class="com.lotusmedia.typesuper.SuperUser"></bean>
</beans>
现在我们执行查看输出:
Normal User Created->com.lotusmedia.typenormal.NormalUser@4cc39a20
Temporary User Created->com.lotusmedia.typenormal.TempUser@485fcf29
Super User Created ->com.lotusmedia.typesuper.SuperUser@a19b1de
我们发现属性注入并没有被执行。这是因为虽然我们加了注解,但是注解的功能没有被开启,所以什么都不会发生。我们修改配置文件。
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
">
<context:annotation-config/>
<bean id="normalUser" class="com.lotusmedia.typenormal.NormalUser"></bean>
<bean id="tempUser" class="com.lotusmedia.typenormal.TempUser"></bean>
<bean id="superUser" class="com.lotusmedia.typesuper.SuperUser"></bean>
</beans>
这次执行我们得到了期望的结果:
Normal User Created->com.lotusmedia.typenormal.NormalUser@679bfb30
Temporary User Created->com.lotusmedia.typenormal.TempUser@7977b9b
Super User Created ->com.lotusmedia.typesuper.SuperUser@37fd6bea
Setting Normal User ->com.lotusmedia.typenormal.NormalUser@679bfb30
Setting Temp User ->com.lotusmedia.typenormal.TempUser@7977b9b
目前看上去不错,现在让我们开始使用@Compent
的注解。首先移除配置文件中bean的注册。
applicationContext.xml :
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
">
<context:annotation-config/>
</beans>
SuperUser.java :
package com.lotusmedia.typesuper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import com.lotusmedia.typenormal.NormalUser;
import com.lotusmedia.typenormal.TempUser;
@Component
public class SuperUser {
private NormalUser normalUser;
private TempUser tempUser;
public SuperUser(){
System.out.println("Super User Created ->"+this);
}
@Autowired
public void setNormalUser(NormalUser normalUser) {
System.out.println("Setting Normal User ->"+normalUser);
this.normalUser = normalUser;
}
@Autowired
public void setTempUser(TempUser tempUser) {
System.out.println("Setting Temp User ->"+tempUser);
this.tempUser = tempUser;
}
}
NormalUser.java :
package com.lotusmedia.typenormal;
import org.springframework.stereotype.Component;
@Component
public class NormalUser {
public NormalUser(){
System.out.println("Normal User Created->"+this);
}
}
TempUser.java :
package com.lotusmedia.typenormal;
import org.springframework.stereotype.Component;
@Component
public class TempUser {
public TempUser(){
System.out.println("Temporary User Created->"+this);
}
}
再次执行程序,我们发现bean都没有,更别说里面的属性了,也就是什么注入都没有执行。这个时候我们就知道annotation-config对@Compent
是不起作用的。该是compents scan出场的时刻了。
修改配置文件,打开compents-scan
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
">
<context:component-scan base-package="com.lotusmedia.typenormal,com.lotusmedia.typesuper"/>
</beans>
再执行就ok了。
Super User Created ->com.lotusmedia.typesuper.SuperUser@426295eb
Normal User Created->com.lotusmedia.typenormal.NormalUser@207f5580
Setting Normal User ->com.lotusmedia.typenormal.NormalUser@207f5580
Temporary User Created->com.lotusmedia.typenormal.TempUser@4f4db0e3
Setting Temp User ->com.lotusmedia.typenormal.TempUser@4f4db0e3
再一次印证了上面的小结,conpents scan能做所有annotaion config 能够做的事情。