How to Use Local Variables as Global in Thymeleaf

Описание: Learn how to properly handle local variables in Thymeleaf forms and utilize their values in your Spring controller seamlessly.
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This video is based on the question https://stackoverflow.com/q/66547733/ asked by the user 'Gabriel Rogath' ( https://stackoverflow.com/u/10412027/ ) and on the answer https://stackoverflow.com/a/66548697/ provided by the user 'shawnz' ( https://stackoverflow.com/u/1631830/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Use Local Variables as Global in Thymeleaf: A Comprehensive Guide

When working with Thymeleaf in a Spring application, you may encounter a scenario where you need to access a local variable across a broader scope, such as in a form submission. This challenge often arises when your variables are defined within a block, making them local and inaccessible outside of that context. If you've found yourself in this situation, you're not alone. In this post, we'll address how to effectively handle local variables in Thymeleaf and make them usable at a global level, ensuring data is correctly submitted in your forms.

Understanding the Problem

In a typical Thymeleaf form, you may have multiple variables, like dateMpya, defined inside a conditional block or iteration. For instance, you might have a dropdown list generated from a collection, and each item in that collection can yield a different local variable:

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However, when the form is submitted, the value of dateMpya does not automatically link to the form submission, leading to confusion and potential errors.

Solution Overview

The goal is to ensure that you can retrieve the value of the selected dateMpya when the user submits the form. Here’s how you can do this effectively by following these steps:

1. Allow form submission to handle selected values

When the user selects a date from the dropdown and submits the form, the selected date is automatically sent to the server as part of the POST request using the name defined for the <select> element. In our example, this is name="date".

2. Update the form action

Remove any unnecessary parts from the th:action attribute and the submit button. By simply relying on the name attribute of the <select>, Spring will automatically include this in the form submission without the need for an extra parameter in the URL.

Before:

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After:

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3. Accessing the selected value in the controller

When the form is submitted, the selected date can be accessed in your Spring controller method through the @ RequestParam annotation:

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Conclusion

By leveraging the built-in features of Thymeleaf and Spring MVC, you can effectively handle local variables and ensure they are properly submitted through forms. Remember, the key takeaway is to utilize the name attribute of the select input without adding unnecessary parameters to the form action or submit button.

If you follow these guidelines, you can simplify your code and enhance its maintainability, while also making it more user-friendly. Enjoy coding with Thymeleaf and Spring!