NoUniqueBeanDefinitionException expected single matching bean but found 2异常的解决办法

NoUniqueBeanDefinitionException: No qualifying bean of type 'xxx' available: expected single matching bean but found 2: x,y的解决办法

一. 异常现象

在利用Spring的@Autowired注入值的时候，出现了如下异常信息:

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'person': Unsatisfied dependency expressed through field 'computer'; nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.yyg.spring.domain.Computer' available: expected single matching bean but found 2: laptop,pc

  at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:587)
  at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:91)
  at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:373)
  at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1350)
  at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580)
  at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503)
  at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
  at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
  at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
  at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
  at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:760)
  at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:869)
  at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)
  at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:144)
  at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:85)
  at com.yyg.spring.SpringTest1.test1(SpringTest1.java:16)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at java.lang.reflect.Method.invoke(Method.java:498)
  at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
  at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
  at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
  at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
  at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
  at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
  at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
  at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
  at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
  at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
  at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
  at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
  at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
  at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
  at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:68)
  at com.intellij.rt.execution.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:47)
  at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:242)
  at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:70)
Caused by: org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type 'com.yyg.spring.domain.Computer' available: expected single matching bean but found 2: laptop,pc
  at org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:215)
  at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1116)
  at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1065)
  at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:584)
  ... 37 more


Process finished with exit code -1

其中异常的核心信息为：

NoUniqueBeanDefinitionException: No qualifying bean of type 'com.yyg.spring.domain.Computer' available: expected single matching bean but found 2:

二. 异常原因

根据异常信息进行分析，很容易发现问题所在：

就是说我们在给'com.yyg.spring.domain.Computer'这个类型的对象赋值的时候，本来是只需要把一个对象赋值给它，结果现在却发现了2个对象，于是Spring容器就不知道到底把哪一个具体的子类赋值给Computer类型了。

三. 解决办法

既然发现了问题的原因，那么解决起来就很容易了。

可以使用@Resource注解或者@Qualifier注解来替代@Autowired注解。

具体用法如下：

方式1：

@Autowired
@Qualifier("laptop")//指明待注入的对象id
private Computer computer;

方式2：

@Resource(name="pc")//指明待注入的对象id
private Computer computer;

四. 知识拓展

• @Autowired：根据类型实现自动装配，从而实现依赖注入；
• @Qualifier("xxx")：根据对象的名称实现依赖注入；
• @Resource(name="xxx")：既根据类型，又根据名称实现依赖注入，是Java自身的注解。