How do you implement form handling with Thymeleaf?

Table of Contents

• Introduction
  • Steps to Implement Form Handling in Thymeleaf
    • 1. Create a Model Class
    • 2. Create a Form in Thymeleaf
    • 3. Create a Controller to Handle the Form Submission
    • 4. Create a Result Template to Display Success Message
  • Handling Validation Errors in Thymeleaf
• Conclusion

Introduction

Form handling is an essential part of many web applications, allowing users to input and submit data. In a Spring Boot application, forms are typically processed using Thymeleaf as the template engine. Thymeleaf simplifies form processing by binding form fields to model objects, allowing seamless communication between the frontend (view) and the backend (controller).

In this guide, we’ll walk through the process of implementing form handling in Spring Boot with Thymeleaf. This includes form creation, data binding, form submission, and validation.

Steps to Implement Form Handling in Thymeleaf

1. Create a Model Class

In Spring Boot, form data is typically bound to a model object. This object contains fields that represent the form inputs. The model class can include annotations like @NotEmpty for validation, but we’ll focus on binding and handling the data.

Model Example:

In this example, the User model has two fields: name and email. It also includes validation annotations to ensure the fields are not empty and meet minimum length requirements.

2. Create a Form in Thymeleaf

The form is defined in a Thymeleaf template, where the form fields are bound to the properties of the model object. The th:field attribute is used to bind a form input to the corresponding field in the model.

Thymeleaf Template (form.html):

• The th:object="${user}" binds the form to the User object, meaning that any field in the form will be associated with the properties of the User model.
• The th:field="*{name}" and th:field="*{email}" bind the name and email fields to the corresponding input fields in the form.

3. Create a Controller to Handle the Form Submission

The controller is responsible for processing the form submission and binding the form data to the model object. It will also perform validation if necessary.

Controller Example:

• The @Valid annotation ensures that validation is performed on the User object before it is passed to the controller method.
• The BindingResult object holds the results of the validation. If there are any validation errors, they will be handled appropriately, and the form will be redisplayed.

4. Create a Result Template to Display Success Message

After successfully submitting the form, you can show a confirmation or result page.

Result Template (result.html):

In this template, the message "User registered successfully!" is displayed if the user data is valid and the form is successfully submitted.

Handling Validation Errors in Thymeleaf

If the form data is invalid, you can display validation error messages next to the form fields using th:errors to bind error messages to specific fields.

Updated Thymeleaf Template (form.html) with Error Handling:

• The th:if="${#fields.hasErrors('name')}" and th:errors="*{name}" expressions check for validation errors related to the name field and display the error message.
• Similarly, the email field has its own validation error display mechanism.

Conclusion

Implementing form handling with Thymeleaf in Spring Boot is a straightforward process that involves creating a form in the Thymeleaf template, binding it to a model object, and processing the form in the controller. By using the @Valid annotation, you can also handle validation and display error messages directly in the view. With these tools, you can easily create interactive, data-driven forms in your Spring Boot applications.