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Iteration and Evalution in Thymeleaf

Introduction​

In this guide, we'll explore Thymeleaf's iteration and conditional evaluation capabilities, focusing on the practical implementation within a web application. We'll cover iteration basics, keeping iteration status, lazy retrieval of data, and conditional evaluation.

Iteration Basics​

The product list page is essential for displaying a collection of products. We utilize Thymeleaf's th:each attribute to iterate over the products and generate HTML dynamically.

<tr th:each="prod : ${prods}">
    <td th:text="${prod.name}">Onions</td>
    <td th:text="${prod.price}">2.41</td>
    <td th:text="${prod.inStock}? #{true} : #{false}">yes</td>
</tr>

Keeping Iteration Status​

Thymeleaf provides a mechanism for keeping track of iteration status using the iterStat variable. This allows us to apply styling or logic based on the current iteration's properties.

<tr th:each="prod, iterStat : ${prods}" th:class="${iterStat.odd}? 'odd'">

Lazy Retrieval of Data​

To optimize data retrieval, Thymeleaf supports lazy loading of context variables. This ensures that data is retrieved only when needed, improving performance.

context.setVariable(
    "users",
    new LazyContextVariable<List<User>>() {
        @Override
        protected List<User> loadValue() {
            return databaseRepository.findAllUsers();
        }
    });

Conditional Evaluation​

Thymeleaf offers simple conditionals (th:if and th:unless) and switch statements (th:switch / th:case) for conditional rendering of HTML elements.

<a href="comments.html" th:href="@{/product/comments(prodId=${prod.id})}" th:if="${not #lists.isEmpty(prod.comments)}">view</a>

Conclusion​

By leveraging Thymeleaf's iteration and conditional evaluation features, we can create dynamic and responsive web pages that adapt to different data scenarios. This enhances user experience and improves the efficiency of our web application.