Spring學習(10)--- @Qualifier注解


  • 按類型自動裝配可能多個bean實例的情況,可以使用Spring的@Qualifier注解縮小范圍(或指定唯一),也可以指定單獨的構造器參數或方法參數
  • 可用於注解集合類型變量

例子:

package com.mypackage;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;

public class MovieRecommender {

	@Autowired
	@Qualifier("main")
	private MovieCatalog movieCatalog;
	
}
package com.mypackage;

import org.springframework.beans.factory.annotation.Qualifier;

public class MovieRecommender {

	private MovieCatalog movieCatalog;

	public void prepare(@Qualifier("main")MovieCatalog movieCatalog){
		this.movieCatalog=movieCatalog;
	}
	
}

PS:應用於構造器的方法比較常用

 

  • XML文件中使用qualifier:
<?xml version="1.0" encoding="UTF-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:context="http://www.springframework.org/schema/context"
        xsi:schemaLocation="http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans-4.1.xsd
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context-4.1.xsd">
         
        <context:component-scan base-package="com.multibean">
        </context:component-scan>   
        
        <bean class="com.mypackage.MovieCatalog">
        	<qualifier value="main"></qualifier>
        </bean>
        
        <bean class="com.mypackage.MovieCatalog">
        	<qualifier value="action"></qualifier>
        </bean>
</beans>
  • 如果通過名字進行注解注入,主要使用的不是@Autowired(即使在技術上能夠通過@Qualifier指定bean的名稱),替代方式是使用JSR-250@Resource注解,它通過其獨特的名稱來定義來識別特定的目標(這是一個與所聲明的類型是無關的匹配過程)
  • 因語義差異,集合或Map類型的bean無法通過@Autowired來注入,因為沒有類型匹配到這樣的bean,為這些bean使用@Resource注解,通過唯一名稱引用集合或Map的bean
  • @Autowired適用於fields,constructors,multi-argument method這些允許在參數級別使用@Qualifier注解縮小范圍的情況
  • @Resource適用於成員變量,只有一個參數的setter方法,所以在目標是構造器或者一個多參數方法時,最好的方式是使用@Qualifier

例子:

先定義一個BeanInterface接口

package com.multibean;

public interface BeanInterface {

}

在定義兩個實現類

package com.multibean;

import org.springframework.stereotype.Component;

@Component
public class BeanInterfaceImpl implements BeanInterface {

}

  

package com.multibean;

import org.springframework.stereotype.Component;

@Component
public class BeanInterface2Impl implements BeanInterface {

}

定義BeanInvoker實現@Qualifier指定bean

package com.multibean;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
public class BeanInvoker {

	@Autowired
	@Qualifier("beanInterfaceImpl")
	private BeanInterface beanInterface;
	
	public void say(){
		
		if(null != beanInterface){
			System.out.println(beanInterface.getClass().getName());
		}else{
			System.out.println("BeanInterface is null.");
		}
		
	}
	
}

單元測試:

package com.multibean;

import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class UnitTest {

	@Test
	public void test(){
		ApplicationContext context = new ClassPathXmlApplicationContext("classpath:spring-beansnnotation.xml");
		BeanInvoker beanInvoker = (BeanInvoker)context.getBean("beanInvoker");
		beanInvoker.say();
	}
}

結果:

七月 06, 2015 11:41:38 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1e397bcb: startup date [Mon Jul 06 23:41:38 CST 2015]; root of context hierarchy
七月 06, 2015 11:41:38 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring-beansnnotation.xml]
com.multibean.BeanInterfaceImpl

 

 

修改BeanInvoker

package com.multibean;


import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

@Component
public class BeanInvoker {

	@Autowired
	@Qualifier("beanInterface2Impl")
	private BeanInterface beanInterface;
	
	public void say(){
		
		if(null != beanInterface){
			System.out.println(beanInterface.getClass().getName());
		}else{
			System.out.println("BeanInterface is null.");
		}
		
	}
	
}

結果:

七月 06, 2015 11:43:38 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1e397bcb: startup date [Mon Jul 06 23:43:38 CST 2015]; root of context hierarchy
七月 06, 2015 11:43:38 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [spring-beansnnotation.xml]
com.multibean.BeanInterface2Impl

 


免責聲明!

本站轉載的文章為個人學習借鑒使用,本站對版權不負任何法律責任。如果侵犯了您的隱私權益,請聯系本站郵箱yoyou2525@163.com刪除。



 
粵ICP備18138465號   © 2018-2025 CODEPRJ.COM