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wanghu198343:
楼主,我的jqgrid有一列设置是可以排序的,点击该列的时候, ...
jqGrid 各种参数 详解(转帖)
GOOD spring <context:annotation-config> 跟 <context:component-scan>诠释及区别 (ZT)
- 博客分类:
- 三大框架之Spring
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<context:annotation-config> 跟 <context:component-scan>诠释及区别
转帖地址:http://blog.csdn.net/baple/article/details/16864835
<context:annotation-config> 和 <context:component-scan>的区别
Difference between <context:annotation-config> vs <context:component-scan>
<context:annotation-config> 是用于激活那些已经在spring容器里注册过的bean(无论是通过xml的方式还是通过package sanning的方式)上面的注解。
<context:component-scan>除了具有<context:annotation-config>的功能之外,<context:component-scan>还可以在指定的package下扫描以及注册javabean 。
下面我们通过例子来详细查看他们的区别,
有三个class A,B,C,并且B,C的对象被注入到A中.
[java] view plaincopyprint?在CODE上查看代码片派生到我的代码片
1.package com.xxx;
2.public class B {
3. public B() {
4. System.out.println("creating bean B: " + this);
5. }
6.}
7.
8.package com.xxx;
9.public class C {
10. public C() {
11. System.out.println("creating bean C: " + this);
12. }
13.}
14.
15.package com.yyy;
16.import com.xxx.B;
17.import com.xxx.C;
18.public class A {
19. private B bbb;
20. private C ccc;
21. public A() {
22. System.out.println("creating bean A: " + this);
23. }
24. public void setBbb(B bbb) {
25. System.out.println("setting A.bbb with " + bbb);
26. this.bbb = bbb;
27. }
28. public void setCcc(C ccc) {
29. System.out.println("setting A.ccc with " + ccc);
30. this.ccc = ccc;
31. }
32.}
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;
}
}
在applicationContext.xml中加入下面的配置 :
<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applicationContext.xml配置文件,将得到下面的结果:
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
OK, 这个结果没什么好说的,就是完全通过xml的方式,不过太过时了,下面通过注解的方式来简化我们的xml配置文件
首先,我们使用autowire的方式将对象bbb和ccc注入到A中:
[java] view plaincopyprint?在CODE上查看代码片派生到我的代码片
1.package com.yyy;
2.import org.springframework.beans.factory.annotation.Autowired;
3.import com.xxx.B;
4.import com.xxx.C;
5.public class A {
6. private B bbb;
7. private C ccc;
8. public A() {
9. System.out.println("creating bean A: " + this);
10. }
11. @Autowired
12. public void setBbb(B bbb) {
13. System.out.println("setting A.bbb with " + bbb);
14. this.bbb = bbb;
15. }
16. @Autowired
17. public void setCcc(C ccc) {
18. System.out.println("setting A.ccc with " + ccc);
19. this.ccc = ccc;
20. }
21.}
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);
}
@Autowired
public void setBbb(B bbb) {
System.out.println("setting A.bbb with " + bbb);
this.bbb = bbb;
}
@Autowired
public void setCcc(C ccc) {
System.out.println("setting A.ccc with " + ccc);
this.ccc = ccc;
}
}
然后,我们就可以从applicationContext.xml中移除下面的配置
<property name="bbb" ref="bBean"/>
<property name="ccc" ref="cBean"/>
移除之后,我们的applicationContext.xml配置文件就简化为下面的样子了
<bean id="bBean"class="com.xxx.B"/>
<bean id="cBean"class="com.xxx.C"/>
<bean id="aBean"class="com.yyy.A"/>
当我们加载applicationContext.xml配置文件之后,将得到下面的结果:
creating bean B: com.xxx.B@5e5a50
creating bean C: com.xxx.C@54a328
creating bean A: com.yyy.A@a3d4cf
OK, 结果是错误的的,究竟是因为什么呢?为什么我们的属性没有被注入进去呢?
是因为注解本身并不能够做任何事情,它们只是最基本的组成部分,我们需要能够处理这些注解的处理工具来处理这些注解
这就是<context:annotation-config> 所做的事情
我们将applicationContext.xml配置文件作如下修改:
<context:annotation-config />
<bean id="bBean"class="com.xxx.B"/>
<bean id="cBean"class="com.xxx.C"/>
<bean id="aBean"class="com.yyy.A"/>
当我们加载applicationContext.xml配置文件之后,将得到下面的结果:
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
OK, 结果正确了
但是如果我们将代码作如下修改:
[java] view plaincopyprint?在CODE上查看代码片派生到我的代码片
1.package com.xxx;
2.import org.springframework.stereotype.Component;
3.@Component
4.public class B {
5. public B() {
6. System.out.println("creating bean B: " + this);
7. }
8.}
9.
10.package com.xxx;
11.import org.springframework.stereotype.Component;
12.@Component
13.public class C {
14. public C() {
15. System.out.println("creating bean C: " + this);
16. }
17.}
18.
19.package com.yyy;
20.import org.springframework.beans.factory.annotation.Autowired;
21.import org.springframework.stereotype.Component;
22.import com.xxx.B;
23.import com.xxx.C;
24.@Component
25.public class A {
26. private B bbb;
27. private C ccc;
28. public A() {
29. System.out.println("creating bean A: " + this);
30. }
31. @Autowired
32. public void setBbb(B bbb) {
33. System.out.println("setting A.bbb with " + bbb);
34. this.bbb = bbb;
35. }
36. @Autowired
37. public void setCcc(C ccc) {
38. System.out.println("setting A.ccc with " + ccc);
39. this.ccc = ccc;
40. }
41.}
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);
}
@Autowired
public void setBbb(B bbb) {
System.out.println("setting A.bbb with " + bbb);
this.bbb = bbb;
}
@Autowired
public void setCcc(C ccc) {
System.out.println("setting A.ccc with " + ccc);
this.ccc = ccc;
}
}
applicationContext.xml配置文件修改为:
<context:annotation-config />
当我们加载applicationContext.xml配置文件之后,却没有任何输出,这是为什么呢?
那是因为<context:annotation-config />仅能够在已经在已经注册过的bean上面起作用。
对于没有在spring容器中注册的bean,它并不能执行任何操作。
但是不用担心,<context:component-scan>除了具有<context:annotation-config />的功能之外,还具有自动将带有@component,@service,@Repository等注解的对象注册到spring容器中的功能。
我们将applicationContext.xml配置文件作如下修改:
<context:component-scan base-package="com.xxx"/>
当我们加载applicationContext.xml的时候,会得到下面的结果:
creating bean B: com.xxx.B@1be0f0a
creating bean C: com.xxx.C@80d1ff
这是什么原因呢?
是因为我们仅仅扫描了com.xxx包及其子包的类,而class A是在com.yyy包下,所以就扫描不到了
下面我们在applicationContext.xml中把com.yyy也加入进来:
<context:component-scan base-package="com.xxx"/>
<context:component-scan base-package="com.xxx,com.yyy"/>
然后加载applicationContext.xml就会得到下面的结果:
creating bean B: com.xxx.B@cd5f8b
creating bean C: com.xxx.C@15ac3c9
creating bean A: com.yyy.A@ec4a87
setting A.bbb with com.xxx.B@cd5f8b
setting A.ccc with com.xxx.C@15ac3c9
哇,结果正确啦 !
回头看下我们的applicationContext.xml文件,已经简化为:
<context:component-scan base-package="com.xxx"/>
<context:component-scan base-package="com.xxx,com.yyy"/>
了。
那如果我们在applicationContext.xml手动加上下面的配置,也就是说既在applicationContext.xml中手动的注册了A的实例对象,同时,通过component-scan去扫描并注册B,C的对象
<context:component-scan base-package="com.xxx"/>
<bean id="aBean"class="com.yyy.A"/>
结果仍是正确的:
creating bean B: com.xxx.B@157aa53
creating bean C: com.xxx.C@ec4a87
creating bean A: com.yyy.A@1d64c37
setting A.bbb with com.xxx.B@157aa53
setting A.ccc with com.xxx.C@ec4a87
虽然class A并不是通过扫描的方式注册到容器中的 ,但是<context:component-scan> 所产生的的处理那些注解的处理器工具,会处理所有绑定到容器上面的bean,不管是通过xml手动注册的还是通过scanning扫描注册的。
那么,如果我们通过下面的方式呢?我们既配置了<context:annotation-config />,又配置了<context:component-scan base-package="com.xxx" />,它们都具有处理在容器中注册的bean里面的注解的功能。会不会出现重复注入的情况呢?
<context:annotation-config /><context:component-scan base-package="com.xxx"/><bean id="aBean"class="com.yyy.A"/>
不用担心,不会出现的:
creating bean B: com.xxx.B@157aa53
creating bean C: com.xxx.C@ec4a87
creating bean A: com.yyy.A@1d64c37
setting A.bbb with com.xxx.B@157aa53
setting A.ccc with com.xxx.C@ec4a87
因为<context:annotation-config />和 <context:component-scan>同时存在的时候,前者会被忽略。也就是那些@autowire,@resource等注入注解只会被注入一次
哪怕是你手动的注册了多个处理器,spring仍然只会处理一次:
[xml] view plaincopyprint?在CODE上查看代码片派生到我的代码片
1.<context:annotation-config />
2.<context:component-scan base-package="com.xxx" />
3.<bean id="aBean" class="com.yyy.A" />
4.<bean id="bla" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
5.<bean id="bla1" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
6.<bean id="bla2" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
7.<bean id="bla3" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
<context:annotation-config />
<context:component-scan base-package="com.xxx" />
<bean id="aBean" class="com.yyy.A" />
<bean id="bla" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
<bean id="bla1" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
<bean id="bla2" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
<bean id="bla3" class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor" />
结果仍是正确的:
creating bean B: com.xxx.B@157aa53
creating bean C: com.xxx.C@ec4a87
creating bean A: com.yyy.A@25d2b2
setting A.bbb with com.xxx.B@157aa53
setting A.ccc with com.xxx.C@ec4a87
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