Generate Spring Boot Server Code with OpenAPI Generator | Exciting Demo

Generate Spring Boot Server Code with OpenAPI Generator | Exciting Demo

Table of Contents:

1. Introduction
2. Understanding the Open API Specification
3. API First Approach
4. Designing the API using Open API Specification 4.1 Open API Definition Version 4.2 API Info 4.2.1 API Title 4.2.2 API Version 4.2.3 API Description 4.3 Server Details 4.4 API Paths 4.4.1 "Save User" API (POST) 4.4.1.1 API Summary 4.4.1.2 API Description 4.4.1.3 API Request Body 4.4.1.4 API Response 4.4.2 "Get User by ID" API (GET) 4.4.2.1 API Summary 4.4.2.2 API Description 4.4.2.3 API Parameters 4.4.2.4 API Response
5. Generating the Server Code using Open API Generator
6. Implementing the Business Logic
7. Starting the Application
8. Testing the APIs in Swagger UI
9. Reactive Code Generation
10. Conclusion

Introduction

In this article, we will explore how to use the Open API Generator to generate server boilerplate code in a Spring Boot application. We will cover both reactive and non-reactive code generation, and demonstrate how to design and implement APIs using the Open API Specification. We will also discuss the API first approach and the benefits of designing APIs before implementing them. By the end of this article, You will have a clear understanding of how to use the Open API Generator, design and implement APIs, and test them using Swagger UI.

Understanding the Open API Specification

The Open API Specification is a language-agnostic standard for describing, consuming, and producing RESTful APIs. It provides a machine-readable description of the API, including details about endpoints, request/response formats, authentication mechanisms, and more. By following the Open API Specification, developers can easily understand and integrate with APIs, saving time and effort in the development process.

API First Approach

The API first approach emphasizes designing and documenting APIs before writing the implementation code. This helps in better planning, collaboration, and decoupling of the API from the underlying implementation. By designing the API first, developers can clearly define the required endpoints, request/response formats, and business logic. This approach also enables easier testing and documentation generation using tools like Swagger UI.

Designing the API using Open API Specification

To design the API, we need to use the Open API Specification and write the API definitions in YAML or JSON format. Let's start by specifying the basic details of our API.

Open API Definition Version

We will be using the Open API version 3.0.1 for our API.

API Info

The API info includes the title, version, and description of the API. Let's define our API info.

API Title

The title of our API will be "User API".

API Version

The version of our API is 1.0.

API Description

The API description will be "User resources API".

Server Details

We need to specify the server details where our API will be hosted. For this example, we will use the local server at "localhost:8080".

API Paths

Now, let's define the paths for our API. We will start by creating two API paths: "Save User" (POST) and "Get User by ID" (GET).

"Save User" API (POST)

API Summary

The summary of this API is "Save user".

API Description

In the description, we will provide more details about the API, including the request body format and the response format.

API Request Body

The request body of this API should be sent in JSON format and should follow the structure defined in the component section. We will Create a model called "UserDTO" and define its properties.

API Response

The response of this API will be the same as the request, which is the "UserDTO" model.

"Get User by ID" API (GET)

API Summary

The summary of this API is "Get user by ID".

API Description

In the description, we will provide more details about the API and mention that the ID parameter is required.

API Parameters

The API parameter will be the ID of the user, which should be sent as a path parameter. It should be of Type STRING and follow the UUID format.

API Response

The response of this API will be the "UserDTO" model.

Generating the Server Code using Open API Generator

Before we can generate the server code, we need to add the required dependencies to our project. We will need the Spring Web dependency for non-reactive code, and the Spring Webflux dependency for reactive code. Once we have added the dependencies, we can start generating the code using the Open API Maven plugin. We need to specify the input file as the API definitions file (api.yaml) and set the generator name as "spring". We also need to specify the Package name pattern where the generated code will be placed.

Implementing the Business Logic

Once we have generated the server code, we can start implementing the business logic of our APIs. For example, in the "Save User" API, we can create a service that saves the user details to a database. We can also add validations to the request body, such as minimum/maximum lengths for certain fields. Similarly, for the "Get User by ID" API, we can create a service that retrieves the user details from the database Based on the ID provided.

Starting the Application

To start the application, we can run it from our Integrated Development Environment (IDE) or by using the Spring Boot command. Once the application is running, we can test our APIs using the Swagger UI.

Testing the APIs in Swagger UI

Swagger UI provides a user-friendly interface to test and document APIs. We can access the Swagger UI by visiting the "localhost:8080/swagger-ui.html" URL in a web browser. In the Swagger UI, we will see the API endpoints, request/response formats, and the ability to execute API calls. We can test our APIs by providing the required parameters and inspecting the response.

Reactive Code Generation

In addition to generating non-reactive code, the Open API Generator also allows us to generate reactive code using the Webflux framework. By specifying the reactive flag as true and adding the required dependencies, we can generate server code that leverages the power of reactive programming. This enables better scalability and performance in our applications.

Conclusion

In this article, we explored how to use the Open API Generator to generate server boilerplate code in a Spring Boot application. We learned about the Open API Specification and the benefits of the API first approach. We designed the API using the Open API Specification, generated the server code, implemented the business logic, and tested the APIs using Swagger UI. Additionally, we also covered reactive code generation using the Webflux framework. By following the steps outlined in this article, you can effectively design, implement, and test APIs in your Spring Boot applications.

Pros:

• The Open API Specification allows for easy integration with other systems.
• Designing APIs using the API first approach improves collaboration and decoupling.

Cons:

• Generating code using the Open API Generator may require some configuration and setup.
• The use of reactive code may introduce complexity, especially for developers unfamiliar with reactive programming.

Highlights:

• Learn how to use the Open API Generator to generate server code in Spring Boot.
• Understand the importance of API first approach in designing and implementing APIs.
• Design and implement APIs using the Open API Specification.
• Test APIs using the Swagger UI.
• Generate reactive code using the Webflux framework.

FAQ:

Q: What is the Open API Specification? A: The Open API Specification is a language-agnostic standard for describing, consuming, and producing RESTful APIs.

Q: Why is the API first approach important? A: The API first approach emphasizes designing and documenting APIs before writing the implementation code, enabling better planning, collaboration, and decoupling of the API from the underlying implementation.

Q: How can I test my APIs using Swagger UI? A: Swagger UI provides a user-friendly interface to test and document APIs. By visiting the "localhost:8080/swagger-ui.html" URL in a web browser, you can access the Swagger UI and test your APIs by providing the required parameters.

Q: What is the AdVantage of generating reactive code? A: Generating reactive code allows for better scalability and performance in applications, leveraging the power of reactive programming and the Webflux framework.