Java 如何在一次操作中使用 Thymeleaf 检查空和空条件？
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How to check null and empty condition using Thymeleaf in one single operation?
提问by Pradeep
Is there any way to check both null and empty condition in Thymeleaf?
有没有办法检查 Thymeleaf 中的空和空条件？
Approach 1
方法一
1) .variable1?.variable2?.variable3
2) variable!=null
3) variable!=''
If we combine two conditions like (variable!='' And variable!=null) I am having issue when rendering.
如果我们结合两个条件，如 (variable!='' And variable!=null) 我在渲染时遇到问题。
I am trying following sample
我正在尝试以下示例
${#strings.concat(#strings.concat('class ',variable1?.variable2), ' ', variable1?.variable2?.variable3)}
I also used containsKeyas well but it is behaving differently.
我也使用了containsKey但它的行为有所不同。
采纳答案by Sumit
In order to check null or empty string using thymeleaf expressions, Use this approach : ---
为了使用 thymeleaf 表达式检查空字符串或空字符串，请使用以下方法：---
<div th:if= "${searchResults.results != null}">
OR, this :--
或这个 ： -
<div th:if= "${searchResults.results != ''}">
Furthermore, you can check the empty or null object on your controller itself and then send the response on your thymeleaf-html page accordingly, like this :--
1.) Your Controller :-
此外，您可以检查控制器本身上的空或空对象，然后相应地在 thymeleaf-html 页面上发送响应，如下所示：--
1.) 您的控制器 :-
List ls = //some data from you DAO
if(ls.isEmpty()){
model.addAttribute("response","NoData");
}else{
model.addAttribute("response",ls);
}
2.) Then on your Thymleaf page :- - -
2.) 然后在您的 Thymleaf 页面上：- - -
<th:block th:if="${response=='NoData'}"> No Data Found </th:block>
PS -I've answered the same question here which helps the questioner hope it helps you as well :-- ThymeLeaf: Not Equal expression in th:if
PS -我在这里回答了同样的问题，这有助于提问者，希望它也能帮助你 :-- ThymeLeaf: Not Equal expression in th:if
回答by naXa
Try ${#strings.isEmpty(variable)}.
试试${#strings.isEmpty(variable)}。
From Tutorial | Using Thymeleaf | Strings:
/*
* Check whether a String is empty (or null). Performs a trim() operation before check
*/
${#strings.isEmpty(name)}
