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spring @Order标记
@Order标记定义了组件的加载顺序。
@Order标记从spring 2.0出现,但是在spring 4.0之前,@Order标记只支持AspectJ的切面排序。spring 4.0对@Order做了增强,它开始支持对装载在诸如Lists和Arrays容器中的自动包装(auto-wired)组件的排序。
在spring内部,对基于spring xml的应用,spring使用OrderComparator类来实现排序。对基于注解的应用,spring采用AnnotationAwareOrderComparator来实现排序。
@Order 标记定义如下:
@Retention(value=RUNTIME)
@Target(value={TYPE,METHOD,FIELD})
@Documented
public @interface Order
这个标记包含一个value属性。属性接受整形值。如:1,2 等等。值越小拥有越高的优先级。
下面让我们来看一个使用spring 3.x 和spring 4.x 的例子:
Ranks.java
package com.javapapers.spring3.autowire.collection;
public interface Ranks {
}
RankOne.java
package com.javapapers.spring3.autowire.collection;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
@Component
public class RankOne implements Ranks{
private String rank = "RankOne";
public String toString(){
return this.rank;
}
}
RankTwo.java
package com.javapapers.spring3.autowire.collection;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
@Component
public class RankTwo implements Ranks{
private String rank = "RankTwo";
public String toString(){
return this.rank;
}
}
RankThree.java
package com.javapapers.spring3.autowire.collection;
import org.springframework.core.annotation.Order;
import org.springframework.stereotype.Component;
@Component
public class RankThree implements Ranks{
private String rank = "RankThree";
public String toString(){
return this.rank;
}
}
Results.java
Component to hold student ranks in a collection as shown below.
package com.javapapers.spring3.autowire.collection;
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class Results {
@Autowired
private List ranks ;
@Override
public String toString(){
return ranks.toString();
}
}
beans.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.springframework.org/schema/beans"
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/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:annotation-config />
<context:component-scan base-package="com.javapapers.spring3"/>
</beans>
RanksClient.java
package com.javapapers.spring3.autowire.collection; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class RanksClient { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); Results results = (Results)context.getBean("results"); System.out.println(results); } }
输出结果:
[RankOne, RankThree, RankTwo]
从结果可以看出,结果是没有顺序的。因为spring 3.x不支持对自动包装组件的排序。
接下来,我升级spring的版本至4.x, 并对RanOne,RankTwo和RankThree加上order标记,值做相应的调整。
@Component
@Order(1)
public class RankOne implements Ranks{
private String rank = "RankOne";
public String toString(){
return this.rank;
}
}
输出结果如下:
[RankOne, RankTwo, RankThree]
参考文章: http://javapapers.com/spring/spring-order-annotation/
spring @Order标记
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