here is a mistake

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'homeController': Unsatisfied dependency expressed through field 'catTestDao'; nested exception is org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'catTestDaoImpl' is expected to be of type [com.websimba.spring.beans.CatTestDaoImpl] but was actually of type [com.sun.proxy.$Proxy22] at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:569) at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:349) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1219) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:543) at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:482) at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306) at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230) at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302) at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197) at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:751) at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:861) at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:541) at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:444) at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:326) at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:107) at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4717) at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5179) at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:724) at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:700) at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734) at org.apache.catalina.startup.HostConfig.manageApp(HostConfig.java:1702) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:482) at org.apache.catalina.mbeans.MBeanFactory.createStandardContext(MBeanFactory.java:431) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.tomcat.util.modeler.BaseModelMBean.invoke(BaseModelMBean.java:300) at com.sun.jmx.interceptor.DefaultMBeanServerInterceptor.invoke(DefaultMBeanServerInterceptor.java:819) at com.sun.jmx.mbeanserver.JmxMBeanServer.invoke(JmxMBeanServer.java:801) at javax.management.remote.rmi.RMIConnectionImpl.doOperation(RMIConnectionImpl.java:1468) at javax.management.remote.rmi.RMIConnectionImpl.access$300(RMIConnectionImpl.java:76) at javax.management.remote.rmi.RMIConnectionImpl$PrivilegedOperation.run(RMIConnectionImpl.java:1309) at javax.management.remote.rmi.RMIConnectionImpl.doPrivilegedOperation(RMIConnectionImpl.java:1401) at javax.management.remote.rmi.RMIConnectionImpl.invoke(RMIConnectionImpl.java:829) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:323) at sun.rmi.transport.Transport$1.run(Transport.java:200) at sun.rmi.transport.Transport$1.run(Transport.java:197) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.Transport.serviceCall(Transport.java:196) at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:568) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:826) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(TCPTransport.java:683) at java.security.AccessController.doPrivileged(Native Method) at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:682) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'catTestDaoImpl' is expected to be of type [com.websimba.spring.beans.CatTestDaoImpl] but was actually of type [com.sun.proxy.$Proxy22] at org.springframework.beans.factory.support.DefaultListableBeanFactory.checkBeanNotOfRequiredType(DefaultListableBeanFactory.java:1480) at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1459) at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1094) at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1056) at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:566) ... 60 more 
 <bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer" p:location="/WEB-INF/jdbc.properties" /> <bean id="dataSource" class="org.apache.commons.dbcp2.BasicDataSource" destroy-method="close" p:driverClassName="com.mysql.jdbc.Driver" p:url="jdbc:mysql://localhost:3306/test" p:username="root" p:password="root" /> <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean"> <property name="dataSource" ref="dataSource"/> <!--<property name="configLocation" value="classpath:hibernate.cfg.xml" />--> <property name="packagesToScan" value="com.spring.model" /> <!--<property name="annotatedPackages" value="com.websimba.spring.model"/>--> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect" >org.hibernate.dialect.MySQL5Dialect</prop> <prop key="hibernate.show_sql" >true</prop> <prop key="current_session_context_class">thread</prop> <prop key="hbm2ddl.auto">update</prop> <prop key="hibernate.charSet">UTF-8</prop> </props> </property> </bean> <tx:annotation-driven transaction-manager="transactionManager" /> <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager"> <property name="sessionFactory" ref="sessionFactory" /> </bean>

in class

 @Component public class CatTestDaoImpl implements CatTestDao { @Autowired private SessionFactory sessionFactory; @Transactional @SuppressWarnings("unchecked") public List<Categories> listCat() { return sessionFactory.getCurrentSession().createQuery("from Categories").list(); } }

in the controller

 @Controller public class HomeController { @Autowired private CatTestDaoImpl catTestDao; @RequestMapping(value = "/", method = RequestMethod.GET) public String home(Map<String,Object> map){ map.put("Categories", new Categories()); map.put("CategoriesList",catTestDao.listCat()); return "home"; } }

What could be the problem or what am I doing wrong?

    1 answer 1

    It’s not true that you are trying to over-autowire a concrete implementation of the CatTestDao interface.

    From a technical point of view, the problem arises from the way Spring handles transactions. In order to be able to open and close a transaction transparently for the developer, Spring, when the component is initialized, creates a proxy object . This object implements the same interfaces as the source component. The proxy object allows Spring to execute some code before / after / instead of the code of the source class method. In the case of transaction management, open a transaction, execute the code of your method, then close the transaction if the method was successful, or roll it back otherwise.

    This situation CatTestDaoImpl : by initializing CatTestDaoImpl , Spring creates in its place a proxy class object that implements the CatTestDao interface. And HomeController requires an object of class CatTestDaoImpl . Since there is no such object in the Spring container, initialization fails. In order for everything to work, you need to autowie-it CatTestDao in HomeController , not CatTestDaoImpl , then the proxy created by Spring will be recognized as a candidate for autowire-ing.

    From an ideological point of view, the appeal to the interface, and not to its specific implementation, makes the program loosely coupled. This allows, if necessary, to replace implementations of interfaces without modifying the code that uses them. For example, you could slip your HomeController 's CatTestDao implementation, which does not receive data from the database, but, for example, through the REST API, and HomeController would not notice the difference. Read the answers to this question , the advantage is explained there in great detail.