In microservices architectures, where multiple services expose their own APIs, having centralized documentation is crucial for developers and consumers. Spring Gateway, acting as the API gateway, can be leveraged to aggregate and present documentation from various services in a unified manner using Springdoc. Let’s explore how to achieve this.

Prerequisites

  • A working Spring Cloud Gateway project.
  • Springdoc enabled in your microservices.

Steps

  1. Configure Springdoc in Microservices

    Ensure each microservice has Springdoc integrated to generate OpenAPI specifications. Include the necessary dependencies and configure basic properties if needed.

  2. Enable Springdoc Gateway Support

    In your Spring Gateway project, add the springdoc-openapi-webflux-ui dependency.

    <dependency>
        <groupId>org.springdoc</groupId>
        <artifactId>springdoc-openapi-webflux-ui</artifactId>
        <version>1.6.15</version> 
    </dependency>
    
  3. Configure Gateway Routes

    Define routes in your gateway to forward requests to the appropriate microservices and their associated documentation endpoints.

    spring:
      cloud:
        gateway:
          routes:
            - id: service-a
              uri: lb://service-a # Replace with your service's URI
              predicates:
                - Path=/service-a/**
              filters:
                - RewritePath=/service-a/(?<path>.*), /$\{path}
            # Add routes for other services similarly
    
  4. Access the Centralized Documentation

    Start your Spring Gateway and microservices. Navigate to http://localhost:8080/swagger-ui.html (adjust the port if necessary) in your browser. You should see a combined documentation page listing APIs from all registered microservices.

Documenting APIs in Code

Springdoc leverages annotations to enrich your API documentation directly within your code. Here’s how to use some common annotations:

  • @Operation: Describes an API operation, providing a summary, description, and tags for categorization.
  • @Parameter: Documents parameters of an operation, specifying their name, description, required status, and data type.
  • @ApiResponse: Describes possible responses of an operation, including status codes, descriptions, and associated data models.
  • @Tag: Groups related operations together under a specific tag.

Example:

@RestController
@RequestMapping("/products")
@Tag(name = "Product Management", description = "Operations related to product management")
public class ProductController {

    @GetMapping("/{id}")
    @Operation(summary = "Get product by ID", description = "Retrieves product details based on ID")
    @ApiResponse(responseCode = "200", description = "Product found")
    @ApiResponse(responseCode = "404", description = "Product not found")
    public Product getProductById(@PathVariable @Parameter(description = "Product ID") Long id) {
        // ... implementation
    }

    // Other endpoints with similar annotations
}

Leveraging @Schema for Model Documentation

The @Schema annotation provides detailed information about data models used in your APIs, making your documentation even more comprehensive. Apply it to classes and fields to describe their properties:

public class Product {

    @Schema(description = "Unique identifier of the product")
    private Long id;

    @Schema(description = "Name of the product")
    private String name;

    @Schema(description = "Price of the product")
    private BigDecimal price;

    // ... other fields and methods
}

Key Points and Considerations

  • Springdoc’s auto-configuration makes setup fairly simple.
  • Gateway routes are critical for directing requests to the correct services and their documentation.
  • For more complex setups, consider using GroupedOpenApi to organize APIs within the combined documentation.
  • Ensure version compatibility between Springdoc and Spring Cloud Gateway.
  • Use annotations judiciously to provide clear and informative documentation.
  • @Schema enhances your documentation by providing details about data models.

Conclusion

Centralized documentation using Spring Gateway and Springdoc provides a streamlined way to understand and interact with your microservices’ APIs. By combining documentation from various services into a single view, you enhance developer experience and simplify API consumption. Documenting APIs within your code using annotations further improves clarity and maintainability. The @Schema annotation adds an extra layer of detail by describing data models.


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By Jeffery Miller

I am known for being able to quickly decipher difficult problems to assist development teams in producing a solution. I have been called upon to be the Team Lead for multiple large-scale projects. I have a keen interest in learning new technologies, always ready for a new challenge.