When learning the AOP configuration of spring, I encountered an error as follows:

Warning: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService' defined in class path resource [applicationContext.xml]: Initialization of bean failed; nested exception is java.lang.NoClassDefFoundError: com/jeremy/service/userServiceImpl (wrong name: com/jeremy/service/UserServiceImpl)

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userService' defined in class path resource [applicationContext.xml]: Initialization of bean failed; nested exception is java.lang.NoClassDefFoundError: com/jeremy/service/userServiceImpl (wrong name: com/jeremy/service/UserServiceImpl)

An error occurred when creating the bean because the class NoClassDefFoundError could not be found

Cause of the problem: the class name of pointcut configured in execution is filled in lowercase by mistake, so an error is reported
solution: change the class name to the correct uppercase

    <aop:config>
        <aop:pointcut id="pointcut" expression="execution(* com.jeremy.service.userServiceImpl.*(..))"/>

        <aop:advisor advice-ref="afterLog" pointcut-ref="pointcut"/>
        <aop:advisor advice-ref="beforeLog" pointcut-ref="pointcut"/>
    </aop:config>

Change to

 <aop:config>
     <aop:pointcut id="pointcut" expression="execution(* com.jeremy.service.UserServiceImpl.*(..))"/>

     <aop:advisor advice-ref="afterLog" pointcut-ref="pointcut"/>
     <aop:advisor advice-ref="beforeLog" pointcut-ref="pointcut"/>
 </aop:config>