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Learn how to effectively capture the selected item in Thymeleaf using forms and controller parameters to enhance your web application logic.
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How to Get the Selected Item on Click in Thymeleaf

When working with Thymeleaf, a common challenge developers face is capturing the selected item from a UI element, such as a button, without triggering actions on page reload or other undesired events. This article will help you understand how to correctly implement this functionality by passing parameters from your Thymeleaf form to your controller efficiently.

The Problem

You may want to call a method with a clicked object as a parameter, but the method is invoked for every element on every reload or button press, causing undesirable behavior.

Here's an illustrative example of a problematic Thymeleaf form:

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In this setup, the onclick method is called whenever you interact with the buttons, which is not what you want.

The Solution

To properly handle item selection and prevent unintended invocations, you can pass parameters to your controller using a simpler approach. Below are two effective methods you can utilize:

Method 1: Using @ RequestParam Annotation

Update Thymeleaf Template: Modify your form and button elements to pass the item's ID as a value to the controller.

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Handle Request in Controller: Use the @ RequestParam annotation in your controller to receive the selected item's ID.

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Method 2: Using @ ModelAttribute with a Model Class

Alternatively, if you prefer to work with a model object, you can use the @ ModelAttribute annotation:

Modify Thymeleaf Template: Set up the form by binding the button field to your model.

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Controller Implementation: In the controller, use the @ ModelAttribute to handle the model data.

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Conclusion

Effectively capturing the selected item in Thymeleaf can streamline interaction and improve your application’s usability. By using either the @ RequestParam approach or the @ ModelAttribute with a model object, you can enhance your controllers without running into the issues associated with default method calls on each interaction.

Integrating these solutions into your Thymeleaf application will result in a smoother user experience. Ensure you test your updates thoroughly to make sure everything functions as expected.