Скачать или смотреть Solving Freemarker Table Rendering Issues for Map of Lists in Spring Boot

Learn how to effectively render tables in Freemarker templates using lists in Spring Boot applications. Resolve common exceptions and improve your email formatting with our detailed guide.
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Solving Freemarker Table Rendering Issues for Map of Lists in Spring Boot

Are you encountering issues while trying to render a table using Freemarker templates in your Spring Boot application? If so, you are not alone. Many developers face similar challenges when it comes to formatting data, especially when dealing with collections like lists and maps. In this guide, we will explore a common exception you might encounter and provide a step-by-step solution to help you successfully render your desired tables in email templates.

Understanding the Issue

The problem arises when you attempt to list a value from a HashMap that contains lists. You may receive an error message similar to the following:

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

This error typically indicates that the data structure you're passing to the Freemarker template is not formatted correctly for iteration in the way it's expected.

Example Scenario

Let's consider a scenario where you're sending an email containing vaccine center information using a Freemarker template. The data you want to render includes a list of MessageRequest objects, which holds details such as center ID, name, pincode, available vaccines, and more.

Here’s a look at your initial code causing the issue:

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

Why This Causes Problems

In the line above, you are putting the map itself into the messages key rather than providing the messageRequests list. As a result, Freemarker cannot iterate over the data as expected, leading to errors.

Solution

Here’s how you can successfully resolve the issue in your Freemarker template rendering process:

Step 1: Update the Data Mapping

Instead of mapping the map to messages, you should map your list of MessageRequest objects (messageRequests) correctly:

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

Step 2: Modify Your Freemarker Template

Next, you need to adjust your Freemarker template to iterate over the messages list properly.

Original Template Snippet:

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

Updated Template Snippet:

Replace it with a simplified list iteration since messages will directly refer to the list of items:

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

Step 3: Test Your Changes

After making these changes, re-run your application to send the email and ensure that the table renders correctly without throwing any exceptions. You should now see the vaccine center information displayed in an organized table format.

Conclusion

Rendering tables in Freemarker templates while using collections in Spring Boot can be challenging, but understanding the way data is passed and correctly formatting your templates can help you overcome these obstacles. By following the steps outlined in this post, you'll now be able to implement dynamic table rendering in your email templates with confidence.

Feel free to reach out in the comments if you have any questions or additional tips on handling Freemarker templates!