How to Properly Receive a DTO with a Map Attribute in a Spring Boot Controller

Learn how to address the "Bad Request" error in your Spring Boot application by using the correct data type for quotes in your DTO.
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Handling DTOs in Spring Boot: Fixing the Bad Request Error

When building REST APIs in Spring Boot, you may encounter issues when receiving data in a Data Transfer Object (DTO). One common problem is getting a Bad Request error when your DTO doesn't match the structure of the incoming JSON. This guide will guide you through how to properly set up your DTO to avoid these errors, specifically when dealing with maps and lists.

The Problem

The error occurs when the controller receives a JSON containing a structure that the corresponding DTO cannot correctly parse. For instance, you might have the following JSON payload sent via Postman:

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And your controller looks like this:

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However, your StockDTO was originally defined as follows:

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Attempting to send this JSON results in a Bad Request error, stating there was a failure deserializing the Map key from the given string "quoteDate".

The Solution

Understanding the Data Structure

To remedy this, you need to understand that the structure of the provided JSON indicates that quotes should be a list rather than a map. In your JSON, quotes is an array of objects, which needs to be reflected in your DTO.

Refactoring the DTO

To fix the issue, we will modify the StockDTO class to properly represent the incoming data structure:

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Defining the Quote Class

Alongside the StockDTO, create a Quote class to encapsulate each individual quote's information:

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JSON Parsing

In practice, if you're using Spring Boot, JSON parsing is typically handled with Jackson, which will take care of converting the JSON payload into your DTO automatically when it's annotated correctly.

Conclusion

By changing the quotes attribute from a Map to a List in your StockDTO, you resolve the issue of deserializing your incoming JSON payload. This will enable your Spring Boot application to properly accept and handle requests without throwing a Bad Request error.

Now you can send the correct JSON to your API effortlessly:

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With this adjustment, the server will process the request without any issues, allowing you to store or manipulate stock quotes as intended. Implement these changes, and enjoy success in your Spring Boot development journey!