Скачать или смотреть Troubleshooting the 400 Bad Request Error in OpenFeign Clients

Discover how to solve the frustrating `400 Bad Request` error when using OpenFeign Clients in a Spring Boot application with this detailed guide.
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This video is based on the question https://stackoverflow.com/q/78124316/ asked by the user 'MarcelTon' ( https://stackoverflow.com/u/7251522/ ) and on the answer https://stackoverflow.com/a/78139231/ provided by the user 'MarcelTon' ( https://stackoverflow.com/u/7251522/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Introduction

If you've been developing with Spring Boot and OpenFeign, you may have encountered a perplexing 400 Bad Request error when trying to execute a valid GET request. This error can drain your time and patience, especially when the same request works flawlessly in Postman. In this guide, we'll dive into a specific case of this error, exploring both the problem and the solution in depth.

The Problem: Understanding the 400 Bad Request

The issue arises when a Spring Boot application, configured with OpenFeign, elicits a 400 Bad Request error during execution of a GET request that should be valid. In our scenario, a request is sent to a defined URL with specific parameters, but the server responds with an error.

To illustrate, here’s a breakdown of the setup:

The application is using Spring (3.1.5) with spring-cloud-starter-openfeign.

A GET request is defined in a Feign client to fetch data based on a filter condition.

Upon calling this GET request through a gateway, a FeignException indicating a 400 Bad Request is thrown even though the URL works perfectly in Postman.

Initial Setup

Dependencies:
The project relies on specific dependencies in its pom.xml, including spring-cloud-starter-openfeign and support for HTTP connections via feign-hc5.

Feign Configuration:
A custom configuration for the Feign client is created that includes a request interceptor.

Client Interface:
The SoClient interface specifies the GET request mapping using the @FeignClient annotation.

Executing Calls:
A gateway component makes calls to SoClient, which throws exceptions when issues arise.

The Key Details from the Error

The error message included:

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

This indicates that the format or headers of the request being sent could be problematic, even though testing the same URL in tools like Postman yields correct results.

The Solution: Narrowing Down the Root Cause

After extensive troubleshooting, the root cause of the 400 Bad Request error was traced to an incorrect handling of HTTP headers due to component scanning. Here's how we resolved it:

Analyze Your Configuration

Check Annotations:
The @EnableFeignClients annotation was placed on the main application class. This was meant to facilitate the processing of configurations, but inadvertently triggered a component scan. As a result, this led to the autowiring of certain request interceptors.

Multiple Headers Issue:
The component scan caused multiple Authorization headers to be added to the RestTemplate request. This is significant because exceeding request header limits or sending duplicate headers can confuse the server.

What We Learned

Clearer Error Messages: While resolving the issue, it became apparent that clearer logging of the error would have sped up the debugging process. Ensure that trace and full logging are enabled when troubleshooting to gather as much context as possible.

Interceptors Handling: Carefully manage how interceptors are wired in your configuration. Isolate them so that they do not override or duplicate headers unexpectedly.

Conclusion

The 400 Bad Request error, while often frustrating, can usually be traced back to configuration issues. In this case, it was the combination of automatic component scanning and interceptor mismanagement that led to the problem. By understanding these nuances, developers can better diagnose and resolve similar issues in their Spring Boot applications using OpenFeign.

Final Thoughts

Next time you encounter a 400 Bad Request, remember to analyze your configuration and how HTTP headers are being managed to save yourself from hours of headbanging!