Thymeleaf: check if a variable is defined

Question

How can I check if a variable is defined in Thymeleaf?

Something like this in Javascript:

if (typeof variable !== 'undefined') { }

or this in PHP:

if (isset($var)) { }

Is there an equivalent in Thymeleaf?

Answer 1

Yes, you can easily check if given property exists for your document using following code. Note, that you're creating div tag if condition is met:

<div th:if="${variable != null}" th:text="Yes, variable exists!">
   I wonder, if variable exists...
</div>

If you want using variable's field it's worth checking if this field exists as well

<div th:if="${variable != null && variable.name != null}" th:text="${variable.name}">
   I wonder, if variable.name exists...
</div>

Or even shorter, without using if statement

<div th:text="${variable?.name}">
   I wonder, if variable.name exists...
</div>`

But using this statement you will end creating div tag whether variable or variable.name exist

You can learn more about conditionals in thymeleaf here

Answer 2

Short form:

<div th:if="${currentUser}">
    <h3>Name:</h3><h3 th:text="${currentUser.id}"></h3>
    <h3>Name:</h3><h3 th:text="${currentUser.username}"></h3>
</div>