Fixing the 400 Bad Request Error in Spring Boot REST API

Learn how to resolve the `400 Bad Request` error when sending JSON data to a Spring Boot REST API, by correctly using the `@ RequestBody` annotation.
---
This video is based on the question https://stackoverflow.com/q/67869992/ asked by the user 'Steve450' ( https://stackoverflow.com/u/14855442/ ) and on the answer https://stackoverflow.com/a/67870130/ provided by the user 'pcsutar' ( https://stackoverflow.com/u/7024049/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: 400 Bad Request when using Spring Boot

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Fixing the 400 Bad Request Error in Spring Boot REST API

Have you ever encountered a frustrating 400 Bad Request error while working with your Spring Boot REST API? If you're finding that your POST requests aren't being handled as expected, you're not alone! Many developers face this challenge, particularly when it involves sending JSON data.

In this guide, we'll dissect a typical scenario that leads to this error and provide you with a clear solution. We’ll explore the necessary steps to fix the issue and ensure your API can correctly process the information being sent.

Understanding the Problem

You might be sending a POST request to your API like this:

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

And the body of your request looks like this:

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

However, your Spring Boot application responds with a 400 Bad Request error, indicating that something is amiss in how the API is processing your request.

What’s Causing the 400 Bad Request Error?

In your Spring Boot controller, the method is defined as follows:

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

Here lies the crux of the problem: you are trying to retrieve the filename variable using @ RequestParam, which is typically used for query parameters in the URL, rather than for data included in the request body.

The Solution

Step 1: Use @ RequestBody

To process JSON data sent in the body of a POST request, you need to use the @ RequestBody annotation. This tells Spring to bind the incoming request body to a method parameter.

Here’s how you can modify your controller to use @ RequestBody:

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

Step 2: Update Request Mapping

Consuming JSON: Make sure you specify that your method consumes application/json to handle JSON request bodies properly.

Produce JSON: Confirm that your method produces application/json responses to maintain the expected format in responses.

Step 3: Test Your Changes

Once you’ve made the necessary adjustments, send your POST request again, ensuring that the body still includes:

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

With the new implementation, your request should be correctly processed without returning a 400 Bad Request error.

Conclusion

Encountering a 400 Bad Request error in Spring Boot can be discouraging, but the solution is fairly straightforward. By properly utilizing the @ RequestBody annotation, you can ensure that your REST API correctly captures and processes the JSON data it receives.

Now, you can go ahead and modify your Spring Boot application confidently! If you have any further questions or need clarification on specific aspects, feel free to reach out!