@RequestMapping("/checkData") public void checkData() { List<User> list = new ArrayList<>(); if(CollectionUtils.isEmpty(list)){ System.out.println(list.size()); list=null; } if(CollectionUtils.isEmpty(list)){ System.out.println("list:"+list); } // StringUtils.hasText(字符串) 字符串存在就是true bu存在就是false //若是字符串裏面的值爲null, "", " ",那麼返回值爲false;不然爲true String temp=""; String temp2=" "; String temp3=null; boolean b = StringUtils.hasText(temp); boolean b2 = StringUtils.hasText(temp2); boolean b3 = StringUtils.hasText(temp3); System.out.println(b); System.out.println(b2); System.out.println(b3); }