Overview The OpenAPI specification allows you to describe your API in a language-agnostic way. Using the OpenAPI Generator tool, you can generate server stubs in numerous programming languages. This guide shows you how to generate a server from an OpenAPI specification and run it locally, providing a quick starting point for developing your API backend.

Prerequisites Before you begin, ensure you have:

An OpenAPI Specification (YAML or JSON): You need a valid OpenAPI document. For example, openapi.yaml. OpenAPI Generator: Install the OpenAPI Generator CLI. For example, using Homebrew run brew install openapi-generator. Using npm run npm install @openapitools/openapi-generator-cli -g. A Chosen Programming Language and Framework: Decide which language and framework you want to generate the server in (Java Spring, Node.js Express, Python Flask, Go Gin, etc.). Step 1: Verify Your OpenAPI Specification Validate your OpenAPI spec: openapi-generator validate -i openapi.yaml

git clone git@github.com:thomasscothamilton/openapi-python-flask.git

If there are errors, correct them before proceeding.

Step 2: Generate the Server Code Use the CLI to generate server stubs. For a Node.js Express server: openapi-generator generate -i openapi.yaml -g nodejs-express-server -o ./generated-server

Parameters: -i openapi.yaml: Input OpenAPI specification file. -g nodejs-express-server: Generator type (change as needed). -o ./generated-server: Output directory.

Refer to the OpenAPI Generator documentation for available generators.

Step 3: Review the Generated Code Navigate to the generated directory: cd generated-server

You’ll find server boilerplate code, a README, and package/build files.

Step 4: Install Dependencies If required, install dependencies. For Node.js: npm install

For other languages, follow the instructions in the generated README (e.g., mvn install for Java, pip install -r requirements.txt for Python).

Step 5: Run the Server Start the server using the instructions provided. For Node.js Express: npm start

For Java Spring: mvn spring-boot:run

For Python Flask: python -m flask run

The server should listen on a default port (e.g., http://localhost:8080 or http://localhost:3000).

Step 6: Test Your Endpoints Use a tool like curl: curl http://localhost:8080/api/v1/example

If the endpoint matches your OpenAPI paths, you’ll see the expected responses.

Step 7: Customize and Implement Business Logic Add business logic to the controller methods, integrate with databases, or adjust routing, security, and middleware as needed. Update and regenerate code if you change the API surface in the OpenAPI spec.