Resolving Thymeleaf Select Dropdown Not Populating Issue in Spring Boot

Описание: Discover how to tackle the `Thymeleaf select dropdown not populating` issue in your Spring Boot app with step-by-step guidance and best practices.
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This video is based on the question https://stackoverflow.com/q/63660967/ asked by the user 'Tokyo' ( https://stackoverflow.com/u/12408652/ ) and on the answer https://stackoverflow.com/a/63677005/ provided by the user 'Wim Deblauwe' ( https://stackoverflow.com/u/40064/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you're developing a Spring Boot application using Thymeleaf for rendering your views, you may have encountered an issue where a select dropdown is not being populated as expected. This problem can be frustrating, especially when you've implemented the dropdown in your HTML code correctly, but the data still fails to display.

In this guide, we will explore the common causes of this issue and provide clear steps to troubleshoot and resolve it effectively.

The Problem: Select Dropdown Not Populating

Scenario Description

You have a Thymeleaf template that includes a form with a select dropdown, which is supposed to populate with values from a list. Here’s a brief overview of the HTML code snippet responsible for the dropdown:

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

Form Bean Structure

Your HomeFormBean class includes the following properties:

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

Initial Data Setup

In your controller, you set up the model attribute as follows:

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

Despite this setup, the select dropdown remains empty. What could be going wrong?

Solution: Steps to Fix the Issue

Understanding the Thymeleaf Expression

The first step is to clarify how Thymeleaf processes the model attributes in your template. In your original dropdown, you used the expression ${paymentServiceTypeList}. This means that paymentServiceTypeList should be available directly in the model, rather than nested within the HomeFormBean object.

Two Possible Solutions

You have two main options to resolve this issue effectively:

Option 1: Update the Controller

Modify the controller to add paymentServiceTypeList directly to the model:

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

This way, the dropdown will successfully reference the list directly, and Thymeleaf will populate it.

Option 2: Update the Thymeleaf Template

Alternatively, you can modify the Thymeleaf template to access the list from the homeFormBean:

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

This adjustment allows Thymeleaf to reference the property correctly, assuming that your HomeFormBean contains the desired list.

Personal Recommendation

While both options are valid, I personally recommend the first one. By updating the controller to directly place paymentServiceTypeList into the model, you simplify the data handling and remove redundancy. Thus, if possible, consider removing the private List<Lookup> paymentServiceTypeList field from the HomeFormBean altogether.

Conclusion

By following the steps outlined above, you should be able to address the issue of the Thymeleaf select dropdown not populating in your Spring Boot application effectively. Ensure that your model attributes are set correctly, and adjust your Thymeleaf expressions accordingly. With these fixes in place, you can enhance the functionality of your form and provide a better user experience.

If you have further questions or encounter specific issues, don’t hesitate to leave a comment or reach out for assistance. Happy coding!