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: