尝试使用@Autowired注释时出现org.springframework.beans.factory.BeanCreationException

Question

我正在创建一个使用Controller，Service和Dao类的应用程序.Service和Dao被创建为使用其实现类实现的接口。我有一个名为UserGroupController的控制器类，其服务为UserGroupService。 。代码片段为：

@Controller
@RequestMapping("module/usergroup")
public class UserGroupController 
{
    @Autowired
    UserGroupService userGroupService;

这个@AutoWired注释导致了这个问题，当我删除那个注释时，一切都正常工作。但是如果我不使用那个注释，每当我尝试访问任何方法我的服务类时，我得到一个空指针例外。

我的服务类如下所示：

@Repository("userGroupService")
public interface UserGroupService

及其实施是：

public class UserGroupServiceImpl implements UserGroupService
{
    @Autowired
    @Qualifier(value = "userGroupDao")
    UserGroupDao userGroupDao;

例外是：

SEVERE: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userGroupController': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.smartwcm.core.user.service.UserGroupService com.smartwcm.admin.user.controller.UserGroupController.userGroupService; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.smartwcm.core.user.service.UserGroupService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    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.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:383)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:283)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:112)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4206)
    at org.apache.catalina.core.StandardContext.start(StandardContext.java:4705)
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057)
    at org.apache.catalina.core.StandardHost.start(StandardHost.java:840)
    at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1057)
    at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:463)
    at org.apache.catalina.core.StandardService.start(StandardService.java:525)
    at org.apache.catalina.core.StandardServer.start(StandardServer.java:754)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:595)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:289)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:414)
Caused by: org.springframework.beans.factory.BeanCreationException: Could not autowire field: com.smartwcm.core.user.service.UserGroupService com.smartwcm.admin.user.controller.UserGroupController.userGroupService; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.smartwcm.core.user.service.UserGroupService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:514)
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:87)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:285)
    ... 28 more
Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [com.smartwcm.core.user.service.UserGroupService] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:949)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:818)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:730)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:486)
    ... 30 more

Answer 1

您应该遵循标准的存储库，服务，控制器模式。

@Controller ：控制器注释用于表示该类是控制器。它包含为http请求提供服务的方法，请求映射在方法级别或类级别完成。
@Service ：使用@Service注释所有服务类。您的所有业务逻辑都将位于服务类中。 Controller和DAO层在那里没有任何业务逻辑。
@Repository ：使用@Repository注释所有DAO类。您的所有数据库访问逻辑都应该在DAO类中。

所以在你的情况下，注释应该是：

@Repository("userGroupDao")
public class UserGroupDaoImpl implements UserGroupDao

@Service("userGroupService")
public class UserGroupServiceImpl implements UserGroupService

@Controller
public class UserGroupController

Answer 2

为何使用@Repository对其进行注释？您可以将它用于DAO课程。

（1）使用 @Service 进行注释

@Service
public interface UserGroupService

（2）或者您可以在Spring配置中将UserGroupService定义为bean：

<bean id="userGroupService" class="com.your.package.UsergroupService" />

Answer 3

如果将@Repository注释移动到实现类，它将起作用。请在下面找到示例代码：

接口类：

public interface Test {
    public void printMessage(String msg);
}

实施班级：

@Repository("testService")
public class TestImpl implements Test {

    @Override
    public void printMessage(String msg) {
    System.out.println(msg);
    }

}

配置类：

@Configuration
@ComponentScan("com.praxissummit.eperf.api.domain.test")
public class TestConfig {

}

主要课程：

public class Main {

    public static void main(String[] args) {
        ApplicationContext ctx = 
           new AnnotationConfigApplicationContext(TestConfig.class);
        ctx.getBean("testService", Test.class).printMessage("Hello world!!");
    }
}

如果我将@Repository注释移动到界面，则弹出No bean named 'testService' is defined

注意：您实际上应该使用@Service注释您的服务类，而不是@Repository

Answer 4

@Autowired有时令人困惑。您可以使用更通用的java @Resource (jsr250)注释。 @Resource表示按名称为我提供已知资源。该名称是从带注释的setter或字段的名称中提取的，或者是从name-Parameter中获取的。 @Resource有一个内置的回退功能，当解析按名称失败时，它会启动。在这种情况下，它会按类型回退到@Autowired - 类型的解决方案。

@Controller
@RequestMapping("module/usergroup")
public class UserGroupController 
{
    @Resource(name="UserGroupService")
    UserGroupService userGroupService;

对于您的服务，您可以选择@Component或@Service

@Service
public interface UserGroupService { }

希望它能解决你的问题。查看@Autowired和@Resource之间的区别，以便更清晰。 @Resource vs @Autowired

@Service或@Component注释用于spring容器，它将动态创建对象。如果您使用@Resource，则甚至可以选择退出上述注释（假设您在服务类的每个位置使用@Resource）

Answer 5

您需要将@Service注释添加到服务类实现中，以便可以通过类路径扫描获取它，添加到Spring上下文中，然后才有资格成为自动装配。

package com.foo.bar.service;

@Service
public class UserGroupServiceImpl implements UserGroupService
{
    @Autowired
    @Qualifier(value = "userGroupDao")
    UserGroupDao userGroupDao;

还要确保如果您的服务类位于包com.foo.bar.service中，那么您的XML包含在组件扫描包标记中。例如：

<context:component-scan base-package="com.foo.bar" />