How to print Array size in thymeleaf?

Besides the util method vphilipnyc described, instead of list.size, use list.size().

When writing list.size, it's trying to call list.getSize() and an List (or a collection) doesn't have a getter named like this.

Try using the utility method for org.thymeleaf.expression.Lists:

<td th:text="${#lists.size(u.engines)}">[Engine Size]</td>