log为啥没有打印

log不会打印？为啥？显示啥的都正常，用syso可以看到调用页面时候的输出。

@RequestMapping(value = "/view", method = RequestMethod.GET)

public String viewCourse(@RequestParam("courseId") Integer courseId,Model model){

System.out.println("this is course controller");

System.out.println("In viewCourse,courseID = {}" + courseId);

log.debug("In viewCourse,courseID = {}" + courseId);

Course course = courseService.getCoursebyId(courseId);

model.addAttribute(course);

return "course_overview";

}