System.out.println(PreferenceUtil.class.getClassLoader().getResource("")); 
                     System.out.println(ClassLoader.getSystemResource("")); 
                     System.out.println(PreferenceUtil.class.getResource("")); 
                     System.out.println(PreferenceUtil.class.getResource("/"));
                     //Class文件所在路径
                     System.out.println(new File("/").getAbsolutePath()); 
                    System.out.println(System.getProperty("user.dir"));