@Autowired与@Resource的区别（一）-优快云博客

本文链接：https://blog.youkuaiyun.com/fenfei_zqh/article/details/79585103

本文探讨了在Spring框架中，@Autowired和@Resource注解在依赖注入时的不同用法。通过一个简单的Human接口及其两个实现类ManImpl和WomanImpl的例子，展示了当存在多个候选bean时，@Resource按名称注入，需指定name属性，而@Autowired按类型注入，遇到冲突时需配合@Qualifier注解明确指定bean名称。

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在spring的使用中，控制反转（IOC），依赖注入(DI)被频繁的使用着。实现自动注入最常用的两个注解@Autowired、 @Resource它们的不同点又在哪里呢？我们通过不同的场景对于它们使用过程中的不同意义了解后再进行原理上的理解。

首先看一个网上简单的例子：
1. 一个简单的Human接口

public interface Human {
    public void speak();
    public void walk();
}

2.两个Human的实现类 ManImpl， WomanImpl

public class ManImpl implements Human {

    @Override
    public void speak() {
        System.out.println(" man speaking ");
    }

    @Override
    public void walk() {
        System.out.println(" man walking ");
    }
}

public class WomanImpl implements Human {
    @Override
    public void speak() {
        System.out.println("woman speaking");
    }

    @Override
    public void walk() {
        System.out.println("woman walking");
    }
}

一个主调方法

@Service
public class SequenceServiceImpl{

    @Resource
    private Human human;
}

启动项目后产生报错信息：

org.springframework.beans.factory.NoUniqueBeanDefinitionException: No qualifying bean of type [com.dotwin.client.api.Human] is defined: expected single matching bean but found 2: manImpl,womanImpl
    org.springframework.beans.factory.config.DependencyDescriptor.resolveNotUnique(DependencyDescriptor.java:172)
    org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1106)
    org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1056)
    org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.autowireResource(CommonAnnotationBeanPostProcessor.java:518)
    org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.getResource(CommonAnnotationBeanPostProcessor.java:496)
    org.springframework.context.annotation.CommonAnnotationBeanPostProcessor$ResourceElement.getResourceToInject(CommonAnnotationBeanPostProcessor.java:627)
    org.springframework.beans.factory.annotation.InjectionMetadata$InjectedElement.inject(InjectionMetadata.java:169)
    org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)
    org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessPropertyValues(CommonAnnotationBeanPostProcessor.java:318)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1219)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543)
    org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482)
    org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
    org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
    org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
    org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
    org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:751)
    org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:861)
    org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541)
    org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:668)
    org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:634)
    org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:682)
    org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:553)
    org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:494)
    org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
    javax.servlet.GenericServlet.init(GenericServlet.java:158)
    org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
    org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
    org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:650)
    org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
    org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
    org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
    org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
    org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    java.lang.Thread.run(Thread.java:748)

我们关注核心的一句报错：No qualifying bean of type [com.dotwin.client.api.Human] is defined: expected single matching bean but found 2: manImpl,womanImpl。意思就是我们有两个实现类，而在注入式并未指定注入哪一个。

@Resouce是按名称进行注入的，如果使用@Resouce解决的办法就是添加name属性指定

@Resource(name = "manImpl")
    private Human human;

@Autowired是按类型进行注入的，如果使用@Autowired注入，解决办法就是添加@Qualifier注解

    @Autowired
    @Qualifier("manImpl")
    private Human human;

@qualifier主要为解决这种问题而产生的一个注解的意思是合格者，通过这个标示，表明了哪个实现类才是我们所需要的，我们修改调用代码，添加@Qualifier注解，需要注意的是@Qualifier的参数名称必须为我们之前定义@Service注解的名称之一，需要注意的是我们这里使用@Service注解，则类生成的bean为默认的类首字母小写命名方式。