How do you handle form submissions with Thymeleaf in Spring?

Table of Contents

Introduction

Handling form submissions in Spring Boot with Thymeleaf is an essential part of creating dynamic web applications. Thymeleaf is tightly integrated with Spring MVC, making it easy to bind form data to Java objects, validate inputs, and process the data submitted by users. By leveraging Thymeleaf’s syntax and Spring Boot’s controller model, you can efficiently manage user input and perform necessary actions on the server-side.

This guide will walk you through the process of handling form submissions using Thymeleaf in Spring Boot, including creating the form, binding form fields to model attributes, and processing the submitted data in a Spring controller.

Step 1: Set Up Your Spring Boot Project

If you haven’t already, create a Spring Boot project and include the necessary dependencies.

Maven Configuration (pom.xml):

Thymeleaf is automatically included with the spring-boot-starter-thymeleaf dependency, and the spring-boot-starter-web will enable your Spring MVC functionality.

Step 2: Create a Form Object (DTO)

In Spring Boot, it's common to use a DTO (Data Transfer Object) or POJO (Plain Old Java Object) to bind form data. This class will represent the data coming from the form submission.

Example: UserForm.java

Step 3: Create the Thymeleaf Form Template

In this step, you’ll create the HTML form that users will interact with. This form will be powered by Thymeleaf’s form binding features, allowing Spring to bind the submitted data to a model object.

Example: userForm.html

Explanation:

  • th:action="@{/submitForm}" sets the form action URL to /submitForm, which is the URL where the form data will be sent when submitted.
  • th:object="${userForm}" binds the form to the userForm model attribute, which is populated by the controller.
  • th:field="*{name}" binds the form field to the name property of the userForm object. This works similarly for the email and age fields.

Step 4: Create the Controller to Handle Form Submission

The controller will handle the GET request to display the form and the POST request to process the form data once it is submitted.

Example: UserController.java

Explanation:

  • The showForm method adds an empty UserForm object to the model and returns the userForm view, which corresponds to the userForm.html Thymeleaf template.
  • The submitForm method processes the form data. The @ModelAttribute("userForm") annotation automatically binds the form fields to the UserForm object. After processing the form, the method adds a success message to the model and returns the formSuccess view, which can display a confirmation message.

Step 5: Create a Success Template

Once the form is submitted successfully, you may want to show a confirmation or success page. This can be achieved by creating another Thymeleaf template, like formSuccess.html.

Example: formSuccess.html

Explanation:

  • This template displays the success message (message), as well as the submitted userForm data.
  • Thymeleaf will populate the placeholders with the data from the userForm object.

Step 6: Run the Application

To run the application, use the following Maven or Gradle command:

Maven:

Gradle:

Visit http://localhost:8080/userForm in your browser to see the form. Upon filling out the form and submitting it, you will be redirected to the success page displaying the submitted data.

Step 7: Optional - Form Validation

If you want to validate the form inputs before processing the data, you can use Spring’s validation annotations (such as @NotNull, @Size, etc.) along with JSR-303 validation and the @Valid annotation in the controller.

Example: Adding Validation to UserForm.java

Updated Controller to Handle Validation

Explanation:

  • The @Valid annotation triggers validation of the UserForm object.
  • The BindingResult is used to capture any validation errors. If there are errors, the form is redisplayed; otherwise, the form data is processed.

Conclusion

Handling form submissions with Thymeleaf in Spring Boot is simple and powerful. By leveraging Thymeleaf's form binding features and Spring MVC's model-binding mechanism, you can easily collect and process user input in a web application. From creating the form to handling submissions and adding validation, Spring Boot and Thymeleaf provide a flexible, robust solution for building dynamic, data-driven web applications.

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