在一个Spring MVC + JPA/Hibernate的训练项目中，我在更改配置后得到了这个错误。
最初的DAO类是这样的：

public Course getById(Integer id) throws DAOException {
        Course result = null;
        try {
            EntityManager em = emf.getFactory().createEntityManager();
            result = em.find(Course.class, id);
        } catch (Exception e) {
            logger.error(e.getMessage(), e);
            throw new DAOException("Could not get Course By Id", e);
        }
        return result;
    }

我被告知要用@PersistenceContext生成 * BattyManager *，并避免不时地创建新的BattyManager。因此，我将上面的EntityManager em = ...行替换为@Autowired EntityManager em;字段，并更改了JpaConfig类，因此它看起来像：

@Configuration
@ComponentScan(basePackages = "com.example.school")
@PropertySource("classpath:database.properties")
@EnableTransactionManagement
public class JpaConfig {
    private final Environment environment;

    @Autowired
    public JpaConfig(Environment environment) {
        this.environment = environment;
    }

    @Autowired
    DataSource dataSource;
    
    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory() throws NamingException {
        LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
        em.setDataSource(dataSource);
        em.setPackagesToScan("com.example.school");
        JpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        em.setJpaVendorAdapter(vendorAdapter);
        return em;
    }

    @Bean
    public PlatformTransactionManager transactionManager(EntityManagerFactory emf) {
        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setEntityManagerFactory(emf);
        return transactionManager;
    }

    @Bean
    public PersistenceExceptionTranslationPostProcessor exceptionTranslation() {
        return new PersistenceExceptionTranslationPostProcessor();
    }
}

以前的配置文件就是这么简单：

@Configuration
public class EntityManagerConfig {
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("PU");

    @Bean
    EntityManager em() {
        return emf.createEntityManager();
    }
}

现在我得到了一个堆栈跟踪，其中有以下最重要的问题：
org.springframework.beans.factory.UnsatisfiedDependencyException.
...
原因：org.springframework.beans.factory.BeanNotOfRequiredTypeException：名为'courseDAO'的Bean应该是'com.example.school.dao.CourseDAO'类型，但实际上是org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency（DefaultListableBeanFactory.java：1317）中的'com.sun.proxy.$Proxy49'类型
这种配置可能有什么问题？