UserService service;

@Autowired
public void setService(UserService service) {
      this.service = service;
}

@Override
public void add(User user) {
       System.out.println(mapper);
       Thread thread = new Thread(new MyRunnable(mapper, user));
       thread.start();
   }


class MyRunnable implements Runnable {

   UserMapper mapper;
   User user;

   public MyRunnable(UserMapper mapper, User user) {
       this.mapper = mapper;
       this.user = user;
       System.out.println(mapper);
       System.out.println(user);
   }

   @Override
   public void run() {
       mapper.insert(user);
   }
}
@Test
public void test1() {
       User u1 = new User(1L,"A");
       service.add(u1);
}

控制台输出

数据库确没数据，又不报错。