Defining Multiple Messages for the Same HTTP Status Code in Spring Boot with Swagger

Discover how to effectively define and manage multiple error messages for the same HTTP status code in your Spring Boot application using Swagger.
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Understanding HTTP Status Codes and Swagger Annotations

In software development, particularly in web applications, HTTP status codes serve as essential indicators of the success or failure of HTTP requests. These codes help clients understand how to proceed based on the server's response. In Spring Boot development, the use of Swagger annotations like @ ApiResponse enables developers to document their APIs effectively, making it clear what each status code represents.

One common question developers encounter is whether it's possible to define multiple messages for the same HTTP status code in Swagger. Let's explore this issue in detail.

The Problem

When defining multiple @ ApiResponse annotations for the same HTTP status code, you might notice that only the first message gets displayed in Swagger UI. For instance, consider the following Swagger annotations in your Spring Boot code:

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In this example, multiple messages for the 400 status code are defined, but only the first message ("message1") will be shown in Swagger documentation. This limitation can be problematic, especially when you want to provide clear descriptions for different error scenarios based on various inputs.

The Solution

Why Only One Message is Displayed

The behavior of displaying only the first message for a duplicated HTTP status code is by design in Swagger. The intention is to keep the API documentation concise and avoid overwhelming users with redundant information. However, this design can be a limitation if you want to convey multiple possible error messages for a single status code.

Alternative Approaches

1. Single Error Message with Context

To represent multiple error scenarios effectively, consider returning a unified error response that includes a list of error messages or a structured error object. For instance:

Define a single error response model that can hold multiple messages.

When an error occurs, populate this model with all relevant messages and return it to the client.

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Using this approach, you can populate the ErrorResponse object with all potential error messages that may arise from the validation process.

2. Custom Response Handling in the API

Another way to manage this issue is to create custom handling in your API method that captures validation errors and formats them into a single response. This method allows you to specify which messages to include based on the context of the request and the validation logic.

Example of Unified Response

Here’s a simple example of how you might implement this in your code:

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In this example, the add method collects potential error messages based on validation and returns a well-structured ErrorResponse.

Conclusion

While Swagger’s design limits the display of multiple error messages for the same HTTP status code, there are effective workarounds. By structuring your error responses wisely and providing context through a unified error response model, you provide clients with valuable information that ensures a better understanding of possible issues.

In summary, embracing a structured approach to error handling not only improves your API's documentation but also enhances the developer experience for those consuming your services.