Скачать или смотреть Resolving Thymeleaf's NumberFormatException Issue: Display Your Custom Error Message

Learn how to customize error messages in Thymeleaf, particularly when dealing with BigInteger validations, to enhance user experience and avoid Java exceptions.
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This video is based on the question https://stackoverflow.com/q/64405838/ asked by the user 'ltome' ( https://stackoverflow.com/u/14289211/ ) and on the answer https://stackoverflow.com/a/64407754/ provided by the user 'Seldo97' ( https://stackoverflow.com/u/13039704/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

When working with web applications in Java using Spring and Thymeleaf, handling user input validation gracefully is crucial. However, developers often encounter issues that can hinder user experience, particularly when default error messages appear instead of custom ones. A common challenge arises during form validation, especially when working with BigInteger, as shown in the scenario where a NumberFormatException is thrown instead of displaying a user-friendly message like "Must be a positive integer." In this post, we will explore how to resolve this problem effectively.

Understanding the Problem

In the provided scenario, you have a form that validates an integer input. You want to display a custom error message when the input doesn't pass validation. However, for BigInteger inputs, Thymeleaf defaults to showing a NumberFormatException. Let’s break down the details:

Current Setup:

Data Model:
Your entity contains a field with a validation annotation:

[[See Video to Reveal this Text or Code Snippet]]

Controller Behavior:
The controller processes the form submission and checks for validation errors:

[[See Video to Reveal this Text or Code Snippet]]

Thymeleaf HTML Template:
Your HTML code tries to render any validation messages:

[[See Video to Reveal this Text or Code Snippet]]

The Challenge:

Despite having a custom error message in the @ Digits annotation, Thymeleaf defaults to a Java exception message instead. This is likely due to Thymeleaf prioritizing bean validation errors over your custom message.

Solution: Customize Error Messages in Thymeleaf

To resolve this issue and display your intended message instead of a Java exception, you can create a messages.properties file in your project's resources folder. Here's how to implement it:

Step-by-Step Solution:

Create the messages.properties file:

Location: src/main/resources/messages.properties

This file will store your custom error messages.

Add the Custom Error Message:
In messages.properties, you need to specify the appropriate key-value pair to map your validation error:

[[See Video to Reveal this Text or Code Snippet]]

Replace entity with the lowercase name of your entity class, ensuring it matches what Thymeleaf expects.

Thymeleaf Configuration:
Thymeleaf automatically reads the messages.properties file, so no additional configuration is typically needed. However, ensure that your Spring configuration is set up to support message source resolution.

Final Validation Check:
After making the above additions, run your application again. When the form validation fails for the myInteger field, Thymeleaf should now retrieve the custom error message from messages.properties rather than displaying a stack trace.

Conclusion

Customizing error messages in Thymeleaf can significantly enhance user experience, allowing for clearer communication of validation issues. By isolating the problem related to BigInteger validations and leveraging a messages.properties file, you can replace default Java exception messages with messages that are meaningful to the users. Implementing these changes ensures that users receive friendly messages like "Must be a positive integer," making form interactions more intuitive and helpful.

In summary, always remember:

Create a messages.properties file.

Include proper keys for type mismatches to reflect your custom messages.

Test thoroughly to ensure the correct messages are displayed.

By following these steps, you can effectively handle validation feedback in any Spring Boot application utilizing Thymeleaf.