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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
user save, id : 2