使用Spring Aop如何配置xml

package com.tgb.aop; public interface UserManager {    public String findUserById(int userId); }   package com.tgb.aop;  public class UserManagerImpl implements UserManager {    public String findUserById(int userId) {     System.out.println("---------UserManagerImpl.findUserById()--------");     if (userId <= 0) {       throw new IllegalArgumentException("该用户不存在!");      }     return "张三";   } }