Caused by: org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'dao' is exp

异常信息:

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'service': Unsatisfied dependency expressed through field 'dao'; nested exception is org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'dao' is expected to be of type 'ifox.DAOImpl' but was actually of type 'com.sun.proxy.$Proxy14'at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:588)at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:88)at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:366)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1264)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:553)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)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:761)at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867)at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543)at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)at ifox.TestDb.<init>(TestDb.java:20)at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)at java.lang.reflect.Constructor.newInstance(Constructor.java:423)at org.junit.runners.BlockJUnit4ClassRunner.createTest(BlockJUnit4ClassRunner.java:217)at org.junit.runners.BlockJUnit4ClassRunner$1.runReflectiveCall(BlockJUnit4ClassRunner.java:266)at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)at org.junit.runners.BlockJUnit4ClassRunner.methodBlock(BlockJUnit4ClassRunner.java:263)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$2.evaluate(ParentRunner.java:268)at org.junit.runners.ParentRunner.run(ParentRunner.java:363)at org.junit.runner.JUnitCore.run(JUnitCore.java:137)at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:117)at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:42)at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:262)at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:84)at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.lang.reflect.Method.invoke(Method.java:498)at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)Caused by: org.springframework.beans.factory.BeanNotOfRequiredTypeException: Bean named 'dao' is expected to be of type 'ifox.DAOImpl' but was actually of type 'com.sun.proxy.$Proxy14'at org.springframework.beans.factory.support.DefaultListableBeanFactory.checkBeanNotOfRequiredType(DefaultListableBeanFactory.java:1510)at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoMatchingBeanFound(DefaultListableBeanFactory.java:1489)at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1104)at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1066)at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:585)... 41 more

今天在看spring注解的时候遇到这个问题可以说弄的自己很难受，我先贴上我的部分错误源码

DAO接口

package ifox;/** * Created by exphuhong on 17-8-14. */public interface DAO{    public Db findDbById(int id);    public void saveBook(Db db);}

DAO实现类

import org.hibernate.Session;import org.hibernate.SessionFactory;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.stereotype.Repository;import javax.annotation.Resource;/** * Created by exphuhong on 17-8-14. */@Repository("dao")public class DAOImpl implements DAO{    @Autowired    private SessionFactory sessionFactory;    //获取和当前线程绑定的Seesion    private Session getSession()    {        return sessionFactory.getCurrentSession();    }    public Db findDbById(int id)    {        String hql = "from Db  WHERE id = ?";        return (Db) getSession().createQuery(hql).setInteger(0, id).uniqueResult();    }    public void saveBook(Db db)    {        getSession().save(db);    }}

Service接口

package ifox;/** * Created by exphuhong on 17-8-14. */public interface Service {        public Db findDbById(int id);        public void saveBook(Db db);}

Service实现类

package ifox;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.beans.factory.annotation.Qualifier;/** * Created by exphuhong on 17-8-14. */@org.springframework.stereotype.Service("service")public class ServiceImpl implements Service {    @Autowired    @Qualifier("dao")    private DAO dao;   //错误用法  private DAOImpl dao;  原理在最下面    public Db findDbById(int id)    {        return dao.findDbById(id);    }    public void saveBook(Db db)    {        dao.saveBook(db);    }}

测试类

package ifox;import org.junit.Test;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.context.ApplicationContext;import org.springframework.context.support.ClassPathXmlApplicationContext;import org.springframework.stereotype.Component;import javax.annotation.Resource;/** * Created by exphuhong on 17-8-14. */public class TestDb {    private ApplicationContext context=null;    private Service service=null;    {        context= new ClassPathXmlApplicationContext("applicationContext.xml");        service = (Service) context.getBean("service");    }    @Test    public void test1() {        System.out.println(context.getBean("dao"));    }    @Test    public void test2()    {        Db db= (Db) service.findDbById(5);        System.out.println(db);    }    @Test    public void test3()    {        service.saveBook(new Db("张飞",21,"1"));    }}

解释：

读者首先需要去了解java的反射机制以及java动态代理。spring注解是实现java注解接口的。注解的实现和java的一样，都是通过反射。通过反射实现动态代理机制，动态代理需要java.lang.reflect.InvocationHandler接口和java.lang.reflect.Prox类的支持。Prox类是专门完成代理的操作类，可以通过此类为一个或多个接口动态生成实现类。

所以这里在获取通过注解的注入的bean时（通过反射将该类（接口的实现类）对应的bean注入到IOC容器中）需要定义成接口类型了只有这样才叫动态代理。