一、寫本博文的原因
有些童鞋搞不為什么要用@Resource或者@Autowired，咱們一起研究下
@Resource默認按照名稱方式進行bean匹配，@Autowired默認按照類型方式進行bean匹配
@Resource(import javax.annotation.Resource;)是J2EE的注解，@Autowired( import org.springframework.beans.factory.annotation.Autowired;)是Spring的注解
Spring屬於第三方的，J2EE是Java自己的東西。使用@Resource可以減少代碼和Spring之間的耦合。
二、@Resource注入
現在有一個接口Human和兩個實現類ManImpl、WomanImpl，在service層的一個bean中要引用了接口Human，這種情況處理如下：
接口Human
-
public interface Human {public void speak();public void walk();}
實現類ManImpl
@Service
public class ManImpl implements Human {
public void speak() {
System.out.println(" man speaking!");
}
public void walk() {
System.out.println(" man walking!");
}
}
實現類WomanImp
@Service
public class WomanImpl implements Human {
public void speak() {
System.out.println(" woman speaking!");
}
public void walk() {
System.out.println(" woman walking!");
}
}
主調類SequenceServiceImpl
@Service
public class SequenceServiceImpl implements SequenceService {
@Resource
private SequenceMapper sequenceMapper;
public void generateId(Map<String, String> map) {
sequenceMapper.generateId(map);
}
//起服務此處會報錯
@Resource
private Human human;
}
這時候啟動tomcat會包如下錯誤：
嚴重: Exception sendingcontext initialized event to listener instance of classorg.springframework.web.context.ContextLoaderListenerorg.springframework.beans.factory.BeanCreationException: Error creating beanwith name 'sequenceServiceImpl': Injection of resource dependencies failed;nested exception isorg.springframework.beans.factory.NoUniqueBeanDefinitionException: Noqualifying bean of type [testwebapp.com.wangzuojia.service.Human] is defined:expected single matching beanbut found 2: manImpl,womanImpl atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:311) atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1214) atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543) atorg.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) atorg.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) atorg.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) atorg.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) atorg.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) atorg.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:772) atorg.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:838) atorg.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:537) atorg.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:446) atorg.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:328) atorg.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:107) atorg.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4717) atorg.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5179)atorg.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183) atorg.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1404) atorg.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1394) atjava.util.concurrent.FutureTask.run(FutureTask.java:266) atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)atjava.lang.Thread.run(Thread.java:745) Caused by:org.springframework.beans.factory.NoUniqueBeanDefinitionException: Noqualifying bean of type [testwebapp.com.wangzuojia.service.Human] is defined: expectedsingle matching bean but found 2: manImpl,womanImpl atorg.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1126) atorg.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1014) atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:508) atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:486) atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:615) atorg.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:169) atorg.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88) atorg.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:308) ...22 more
報錯的地方給我們提示了:but found 2: manImpl,womanImpl 意思是Human有兩個實現類。解決方案如下：
@Service
public class SequenceServiceImpl implements SequenceService {
@Resource
private SequenceMapper sequenceMapper;
public void generateId(Map<String, String> map) {
sequenceMapper.generateId(map);
}
@Resource(name = "manImpl")//注意是manImpl不是ManImpl，因為使用@Service，容器為我們創建bean時默認類名首字母小寫
private Human human;
}
這樣啟動服務就不會報錯了。如果是使用的@Autowired注解，要配上@Qualifier("manImpl")，代碼如下：
@Service
public class SequenceServiceImpl implements SequenceService {
@Resource
private SequenceMapper sequenceMapper;
public void generateId(Map<String, String> map) {
sequenceMapper.generateId(map);
}
@Autowired
@Qualifier("manImpl")
private Human human;
}
希望對你有幫助，歡迎交流+QQ3245792286