How to do if-else in Thymeleaf?

Question

What's the best way to do a simple if - else in Thymeleaf?

I want to achieve in Thymeleaf the same effect as

<c:choose>
  <c:when test="${potentially_complex_expression}">
     <h2>Hello!</h2>
  </c:when>
  <c:otherwise>
     <span class="xxx">Something else</span>
  </c:otherwise>
</c:choose>

in JSTL.

What I've figured so far:

<div th:with="condition=${potentially_complex_expression}" th:remove="tag">
    <h2 th:if="${condition}">Hello!</h2>
    <span th:unless="${condition}" class="xxx">Something else</span>
</div>

I don't want to evaluate potentially_complex_expression twice. That's why I introduced local variable condition . Still I don't like using both th:if="${condition} and th:unless="${condition}" .

An important thing is that I use two different HTML tags: let's say h2 and span .

Can you suggest a better way to achieve it?

Answer 1

Thymeleaf has an equivalent to <c:choose> and <c:when> : the th:switch and th:case attributes introduced in Thymeleaf 2.0.

They work as you'd expect, using * for the default case:

<div th:switch="${user.role}"> 
  <p th:case="'admin'">User is an administrator</p>
  <p th:case="#{roles.manager}">User is a manager</p>
  <p th:case="*">User is some other thing</p> 
</div>

See this for a quick explanation of syntax (or the Thymeleaf tutorials).

Disclaimer : As required by StackOverflow rules, I'm the author of Thymeleaf.

Answer 2

I tried this code to find out if a customer is logged in or anonymous. I did using the th:if and th:unless conditional expressions. Pretty simple way to do it.

<!-- IF CUSTOMER IS ANONYMOUS -->
<div th:if="${customer.anonymous}">
   <div>Welcome, Guest</div>
</div>
<!-- ELSE -->
<div th:unless="${customer.anonymous}">
   <div th:text=" 'Hi,' + ${customer.name}">Hi, User</div>
</div>

Answer 3

I'd like to share my example related to security in addition to Daniel Fernández.

<div th:switch="${#authentication}? ${#authorization.expression('isAuthenticated()')} : ${false}">
    <span th:case="${false}">User is not logged in</span>
    <span th:case="${true}">Logged in user</span>
    <span th:case="*">Should never happen, but who knows...</span>
</div>

Here is complex expression with mixed 'authentication' and 'authorization' utility objects which produces 'true/false' result for thymeleaf template code.

The 'authentication' and 'authorization' utility objects came from thymeleaf extras springsecurity3 library . When 'authentication' object is not available OR authorization.expression('isAuthenticated()') evaluates to 'false', expression returns ${false}, otherwise ${true}.

Answer 4

You can use

If-then-else:  (if) ? (then) : (else)

Example:

'User is of type ' + (${user.isAdmin()} ? 'Administrator' : (${user.type} ?: 'Unknown'))

It could be useful for the new people asking the same question.

Answer 5

Another solution - you can use local variable:

<div th:with="expr_result = ${potentially_complex_expression}">
    <div th:if="${expr_result}">
        <h2>Hello!</h2>
    </div>
    <div th:unless="${expr_result}">
        <span class="xxx">Something else</span>
    </div>
</div>

More about local variables:
http://www.thymeleaf.org/doc/tutorials/2.1/usingthymeleaf.html#local-variables

Answer 6

在更简单的情况下（当 html 标签相同时）：

<h2 th:text="${potentially_complex_expression} ? 'Hello' : 'Something else'">/h2>

Answer 7

Another solution is just using not to get the opposite negation:

<h2 th:if="${potentially_complex_expression}">Hello!</h2>
<span class="xxx" th:if="${not potentially_complex_expression}">Something else</span>

As explained in the documentation , it's the same thing as using th:unless . As other answers have explained:

Also, th:if has an inverse attribute, th:unless , which we could have used in the previous example instead of using a not inside the OGNL expression

Using not also works, but IMHO it is more readable to use th:unless instead of negating the condition with not .

Answer 8

Use th:switch as an if-else

<span th:switch="${isThisTrue}">
  <i th:case="true" class="fas fa-check green-text"></i>
  <i th:case="false" class="fas fa-times red-text"></i>
</span>

Use th:switch as a switch

<span th:switch="${fruit}">
  <i th:case="Apple" class="fas fa-check red-text"></i>
  <i th:case="Orange" class="fas fa-times orange-text"></i>
  <i th:case="*" class="fas fa-times yellow-text"></i>
</span>

Answer 9

<div th:switch="${user.role}"> 
<p th:case="'admin'">User is an administrator</p>
<p th:case="#{roles.manager}">User is a manager</p>
<p th:case="*">User is some other thing</p> 
</div>


<div th:with="condition=${potentially_complex_expression}" th:remove="tag">
<h2 th:if="${condition}">Hello!</h2>
<span th:unless="${condition}" class="xxx">Something else</span>
</div>

Answer 10

<div style="width:100%">
<span th:each="i : ${#numbers.sequence(1, 3)}">
<span th:if="${i == curpage}">
<a href="/listEmployee/${i}" class="btn btn-success custom-width" th:text="${i}"></a
</span>
<span th:unless="${i == curpage}">
<a href="/listEmployee/${i}" class="btn btn-danger custom-width" th:text="${i}"></a> 
</span>
</span>
</div>

enter image description here

Answer 11

<div th:switch="true"> 
    <div th:case="${condition}=='1'">answer1...</div>
    <div th:case="${condition}=='2'">answer2...</div>
    <div th:case="*">answer3...</div> 
</div>

Answer 12

当我想根据用户的性别显示照片时，这对我有用：

<img th:src="${generou}=='Femenino' ? @{/images/user_mujer.jpg}: @{/images/user.jpg}" alt="AdminLTE Logo" class="brand-image img-circle elevation-3">

Answer 13

If-then-else have 2 variant.

First:
<form method="get" th:action="@{/{id}(id=${user.isAdmin()}?'admin':'user')}"> <input type="submit" value="to Main"/></form>

Second: <th:block th:if!="${branchMessages.isEmpty()}"> ... </th:block> <th:block th:unless="${branchMessages.isEmpty()}"> ... </th:block>

Answer 14

If and unless sometimes fail to provide the expected result when using 2 separated blocks. If and else can also be achieved by using if statement in the first block for condition 1 (TRUE) and the second if statement is the second block for alternative choice when the first condition fails (FALSE).

Hoping that this will help.

<div th:with="condition=${potentially_complex_expression}" th:remove="tag">
   //True
   <h2 th:if="${if_condition}">Hello!</h2>

   //False
   <h2 th:if="${alternative_for_false}">Something else</h2>
</div>