How to check null and empty condition using Thymeleaf in one single operation?

Question

Is there any way to check both null and empty condition in Thymeleaf?

Approach 1

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.

I am trying following sample

${#strings.concat(#strings.concat('class ',variable1?.variable2), ' ', variable1?.variable2?.variable3)}

I also used containsKey as well but it is behaving differently.

Answer 1

Try ${#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)}

Answer 2

In order to check null or empty string using thymeleaf expressions, Use this approach : ---

<div th:if= "${searchResults.results != null}">

OR, this :--

<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 :-

 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 :- - -

<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