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关于Spring3.2.0中@Autowire默认配置的测试

news 2026/7/28 18:00:08

spring2.5.6版本中@Autowire默认的是ByType，如果在beans.xml中配置了多个相同类型的bean（class相同），在注入时如果不显示的指定哪个bean则会出现报错。

今天测试了一下Spring3.2.0中@Autowire，发现同spring2.5.6版本中略有不同，Spring3.2.0中@Autowire的默认注入方式也是ByTpye,只是在存在多个类型相同的bean的情况下没有显示的指定bean时，spring会去采用ByName的方式去尝试注入，如果此时容器中没有相应的bean才会抛出异常。

测试

测试@Autowire的默认方式

beans.xml <context:annotation-config /> //该bean的id没有和UserService 对应的属性名相同 <bean id="userDao2" class="dao.impl.UserDaoImpl"> <property name="id" value="2"></property> </bean> <bean id="userService" class="service.UserService"> </bean>

UserDaoImpl .java public class UserDaoImpl implements UserDao { private int id; public int getId() { return id; } public void setId(int id) { this.id = id; } public void save(User u) { System.out.println("user save, id : " + id); } public void other() { System.out.println("other"); } }

UserService .java public class UserService { private UserDao userDao; @Autowired public void setUserDao(UserDao userDao) { this.userDao = userDao; } public void add(User u) { userDao.save(u); } public UserDao getUserDao() { return userDao; } }

//测试代码 public class UserServiceTest { @Test public void test() { ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml"); UserService userService = (UserService) context.getBean("userService"); userService.add(new User()); } }

输出

user save, id : 2

证明@Autowire的默认注入方式是ByType

测试多个类型相同时@Autowire的默认注入方式

修改配置文件

beans.xml <context:annotation-config /> //该bean的id没有和UserService 对应的属性名相同 <bean id="userDao2" class="dao.impl.UserDaoImpl"> <property name="id" value="2"></property> </bean> //该bean的id没有和UserService 对应的属性名相同 <bean id="userDao1" class="dao.impl.UserDaoImpl"> <property name="id" value="1"></property> </bean> <bean id="userService" class="service.UserService"> </bean>

输出

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire method: public void service.UserService.setUserDao(dao.UserDao); nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [dao.UserDao] is defined: expected single matching bean but found 2: [userDao2, userDao1] at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:288) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1120) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:522) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:461) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:607) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139) at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83) at UserServiceTest.test(UserServiceTest.java:16) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) 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$2.evaluate(ParentRunner.java:268) at org.junit.runners.ParentRunner.run(ParentRunner.java:363) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:89) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:41) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:541) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:763) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:463) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:209) Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire method: public void service.UserService.setUserDao(dao.UserDao); nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [dao.UserDao] is defined: expected single matching bean but found 2: [userDao2, userDao1] at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:601) at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285) ... 36 more Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [dao.UserDao] is defined: expected single matching bean but found 2: [userDao2, userDao1] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:825) at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:730) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:558) ... 38 more

expected single matching bean but found 2: [userDao2, userDao1]可以发现出现的异常的原因是有多个相同类型的bean。

测试@Autowire默认下，容器存在多个相同类型的bean，且含有与属性name相同的bean

修改bean.xml配置

<context:annotation-config /> <bean id="userDao2" class="dao.impl.UserDaoImpl"> <property name="id" value="2"></property> </bean> //与属性name相同 <bean id="userDao" class="dao.impl.UserDaoImpl"> <property name="id" value="1"></property> </bean> <bean id="userService" class="service.UserService"> </bean>

输出

user save, id : 1

证明在@Autowire在默认下以ByType方式注入失败时会尝试使用，ByName方式去注入，如果还是失败则抛出异常。

总结

@Autowire在默认下以ByType方式注入失败时，会尝试使用ByName方式去注入，如果还是失败则抛出异常。
在存在多个相同bean时，可以使用@Qualifier注解去显示的指定使用哪个bean，是上面的配置不变，修改UserService，添加@Qualifier注解

public class UserService { private UserDao userDao; @Autowired public void setUserDao(@Qualifier("userDao2")UserDao userDao) { this.userDao = userDao; } public UserDao getUserDao() { return userDao; } public void add(User u) { userDao.save(u); } }

输出