Enterprise Java

Swagger Codegen Tutorial

In this article, we will explain the Swagger Codegen.

1. Introduction

The OpenAPI specification defines the standard of describing HTTP API for any project. This is programming-language agnostic. This helps humans and computers to know about the System/API without the need to look into the code. If the specification is properly implemented it helps a consumer to understand the interaction with the remote system effectively without much hassle.

OpenAPI specification can be compared to an Interface in Java. Interfaces in Java define the contract between the client and the server. It tells the caller what it needs to send and the expected value which will be returned. This helps the caller to reduce the guesswork. Similarly, OpenAPI is a specification that defines how to document your HTTP API so that the consumer of your API has to do minimal guesswork.

One of the big use cases for a machine-readable API definition is to automatically generate the Client code. The OpenAPI documents are generally described in YAML or JSON. The best part is that these documents can be created statically or generated at runtime. One this to note is that OpenAPI can not be integrated with all the available HTPP API implementations – but they are available for RESTful HTTP Apis. The current version of OpenAPI specification is 3.1.0.

2. Swagger Codegen

Swagger codegen allows generation of API client libraries. It also allows you to create the stubs for the server and also helps in generation of documentation for the API. If you have an existing swagger specification you can generate the code using the below command:

swagger-codegen generate -i  -l 

Please note that you can only use the above statement if you have Homebrew installed. If you don’t then you can use the below command:

java -jar swagger-codegen-cli-2.2.1.jar generate -i  -l 

The -i parameter is used to specify the path to your API’s specification. The -l parameter is used to specify the language you want to generate the code for your specified API’s spec. It also creates a README file with all the information you need to know how to run the application.

One can also generate an API client or server using the online generators. For more information about how to generate the server, stubs refer to the Swagger documentation here.

3. Summary

In this article, we looked at the OpenAPI specification. We discussed the use case for it and also looked at the Swagger Codegen tool which is used to generate the API client libraries and Server stubs. If you want to read more, you can refer here.

Mohammad Meraj Zia

Senior Java Developer
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