创建自定义的限定符

​ 我们可以为bean设置自己的限定符,而不是依赖于将bean ID作为限定符.在这里所需要做的就是在bean声明上添加@Qualifier注解来进行更加明确的区分.例如:

Animal接口:

package com.home.quar;

public interface Animal {
    public void eat();

}

Cat:

package com.home.quar;

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

@Component
@Qualifier("cat")
public class Cat implements Animal {
    @Override
    public void eat() {
        System.out.println("猫吃鱼");
    }
}

Panda:

package com.home.quar;

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

@Component
@Qualifier("panda")
public class Panda implements  Animal {
    @Override
    public void eat() {
        System.out.println("熊猫吃竹子");
    }
}

TestDemo:

package com.home.quar;

import org.junit.Test;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TeatDemo {

    @Autowired
    @Qualifier(value = "cat")
    private Animal animal;
    public void setAnimal(Animal animal) {
        this.animal = animal;
    }

    public Animal getAnimal() {
        return animal;
    }

    @Test
    public void demo() {
        ApplicationContext app = new ClassPathXmlApplicationContext("classpath:application.xml");
        TeatDemo bean = (TeatDemo) app.getBean("teatDemo");
        System.out.println(bean.getAnimal());
        Animal al = bean.getAnimal();
        if (al instanceof Cat) {
            System.out.println("Cat");
        } else if (al instanceof Panda) {
            System.out.println("Panda");
        }
        al.eat();

        try {
            app.getBean("panda");
        } catch (Exception e) {
            if (e instanceof NoSuchBeanDefinitionException) {
                System.out.println("@Qualifier不能作为Bean的标识符");
            }
            e.printStackTrace();
        }
    }

}

最终结果是被@Qualifier注解的类被注入了进来,当然我们也可以用 XML配置的方法来限定@Qualifier的注入:

<?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-4.3.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd" >
      <context:annotation-config/>
      <bean id="teatDemo" class="com.home.quar.TeatDemo"/>
      <bean id="cat" class="com.home.quar.Cat">
            <qualifier type="org.springframework.beans.factory.annotation.Qualifier"   value="cat"/>
      </bean>
      <bean id="panda" class="com.home.quar.Panda">
            <qualifier type="org.springframework.beans.factory.annotation.Qualifier"  value="panda"/>
      </bean>
</beans>

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