Spring Bean工厂注解之@Autowired + @Qualifier指定接口实现类

在IntelliJ Idea中新建SpringBoot工程
在service层新建用于测试的接口及两个实现类：
QualifierService.java

package com.jake.singlecandy.service;

public interface QualifierService {

    int getIndexOfImpl();

}

QualifierServiceImpl1.java

package com.jake.singlecandy.service.impl;

import com.jake.singlecandy.service.QualifierService;
import org.springframework.stereotype.Service;

@Service
public class QualifierServiceImpl1 implements QualifierService {

    @Override
    public int getIndexOfImpl() {
        return 1;
    }
}

QualifierServiceImpl2.java

package com.jake.singlecandy.service.impl;

import com.jake.singlecandy.service.QualifierService;
import org.springframework.stereotype.Service;

@Service
public class QualifierServiceImpl2 implements QualifierService {

    @Override
    public int getIndexOfImpl() {
        return 1;
    }
}

首先仅仅使用@Autowired进行自动注入，单元测试代码如下：

    @Autowired
    private QualifierService qualifierService;

    @Test
    public void testAutowired() {
        int indexOfImpl = qualifierService.getIndexOfImpl();
        System.out.println("index of impl is " + indexOfImpl);
    }

此时没有使用@Qualifier指定实现类
执行单元测试方法，控制台报错：

Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.jake.singlecandy.service.QualifierService' available: expected single matching bean but found 2: qualifierServiceImpl1,qualifierServiceImpl2
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:215)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1113)
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1062)
	at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:583)
	... 28 more

由报错可知，没有指定实现类
所以单元测试中注入部分的代码添加@Qualifier注解指定实现类：

    @Autowired
    @Qualifier("qualifierServiceImpl2")
    private QualifierService qualifierService;

再次执行单元测试方法，得到输出结果：

index of impl is 2

对Bean工厂注解id的说明
以QualifierServiceImpl2为例，如果在@Service注解中没有填写bean id，那么默认为@Service("qualifierServiceImpl2")，即id默认为类名首字母小写。相当于XML中的配置：

<bean id="qualifierServiceImpl2" class="com.jake.singlecandy.service.impl.QualifierServiceImpl2"/>

指定实现类时应为：

@Qualifier("qualifierServiceImpl2")

如果填写了bean id：

@Service("QualifierService2 ")
public class QualifierServiceImpl2 implements QualifierService {

    @Override
    public int getIndexOfImpl() {
        return 1;
    }
}

那么相当于XML配置：

<bean id="qualifierService2" class="com.jake.singlecandy.service.impl.QualifierServiceImpl2"/>

指定实现类时应为：

@Qualifier("qualifierService2")