@Qualifier 注解不起作用

 

 Animal  动物类接口

package cn.blogspring.chapter2.pojo.definition;

/**
 * @Author: qiuj
 * @Description:动物接口
 * @Date: 2018-12-29 19:41
 */
public interface Animal {
    void use();
}

 实现类　　：dog

package cn.blogspring.chapter2.pojo;

import cn.blogspring.chapter2.pojo.definition.Animal;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;

/**
 * @Author: qiuj
 * @Description:
 * @Date: 2018-12-29 19:45
 */
@Component()
public class Dog implements Animal {

    @Override
    public void use() {
        System.out.println("狗【"+ Dog.class.getSimpleName()+"】是看门用的。");
    }


}

实现类　　：cat 

package cn.blogspring.chapter2.pojo;

import cn.blogspring.chapter2.pojo.definition.Animal;
import org.springframework.context.annotation.Primary;
import org.springframework.stereotype.Component;

/**
 * @Author: qiuj
 * @Description:
 * @Date: 2018-12-29 20:10
 */
@Component
public class Cat implements Animal {
    @Override
    public void use() {
        System.out.println("猫【"+ Cat.class.getSimpleName() +"】是抓老鼠。");
    }
}

 BussinessPerson 人类实现类

package cn.blogspring.chapter2.pojo;


import cn.blogspring.chapter2.pojo.definition.Animal;
import cn.blogspring.chapter2.pojo.definition.Person;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Component;

/**
 * @Author: qiuj
 * @Description:    人类实现类
 * @Date: 2018-12-29 19:42
 */
@Component
public class BussinessPerson implements Person {
    
    @Autowired
    @Qualifier("cat")
    private Animal animal = null;

    @Override
    public void service() {
        this.animal.use();
    }

    @Autowired
    @Override
    public void setAnimal(Animal animal) {
        this.animal = animal;
    }
}

当人类类   设置   animal  动物类的时候，由于有两个实现类  ， 产生了歧义性 ，Ioc  容器不知道注入哪个，

使用 @Qualifier("cat") 设置为注入  cat的Bean

却发现始终注入不进去  ， 异常信息：发现了两个 实现类  不知道如何区分

20:59:24.179 [main] WARN org.springframework.context.annotation.AnnotationConfigApplicationContext - Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'bussinessPerson': Unsatisfied dependency expressed through method 'setAnimal' parameter 0; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'cn.blogspring.chapter2.pojo.definition.Animal' available: expected single matching bean but found 2: cat,dog
Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'bussinessPerson': Unsatisfied dependency expressed through method 'setAnimal' parameter 0; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'cn.blogspring.chapter2.pojo.definition.Animal' available: expected single matching bean but found 2: cat,dog
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:676)
	at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:374)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1378)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:575)
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:498)
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:846)
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:863)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:546)
	at org.springframework.context.annotation.AnnotationConfigApplicationContext.<init>(AnnotationConfigApplicationContext.java:88)
	at cn.blogspring.chapter2.config.IocTest.main(IocTest.java:36)
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'cn.blogspring.chapter2.pojo.definition.Animal' available: expected single matching bean but found 2: cat,dog
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:217)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1215)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1164)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:668)
	... 14 more

 结果导致原因在于  虚拟机在初始化类的时候，先执行的流程是所有的 @Autowired  

所以当走到set 方法上的 Autowired ,Ioc 容器在这时候就要做决定了，   就不知道选择那个实现类了

    @Override
    @Autowired
    public void setAnimal(Animal animal) {
        this.animal = animal;
    }

所以 去掉 set方法上的 @Autowired  ,不要让他在set方法就进行注入，就可以了