---
title: "The quick guide to API First development with JHipster"
date: 2020-06-15T00:00:00+00:00
author: "poornerd"
tags: ["jhipster", "api", "swagger", "openapi"]
canonical: https://www.poornerd.com/2020/06/15/guide-to-api-first-development-with-jhipster.html
source: Raw Markdown twin of the HTML article; content is the original source.
---
Many have written API's and then genereated [Swagger](https://swagger.io) documentation based on the annotated code.  

This is not what I am talking about.  The idea is that you design the API you (your customer) will need, and describe it using [Open API 3.0 Specification](https://swagger.io/specification/).  Once your API is specified, you generate the interfaces and stubs to mock the endpoints and then implement them.

[JHipster](https://www.jhipster.tech) has provided a [method for API-First development](https://www.jhipster.tech/doing-api-first-development/) by integrating [swagger-codegen](https://github.com/swagger-api/swagger-codegen) into the project.

The quick version of the steps to API-First development with JHipster are:
1. Put your api.xml (Open API 3.0 spec) in ```src/main/resources/swagger/api.yml```
1. Generate the sources with ```./gradlew openApiGenerate```(or just start the project)
1. Look at the code generated in ```${buildDirectory}/generated-sources/openapi/src/main/java/${package}/web/api/```
1. Implement ```@Service``` classes which implement the generate interfaces looking something like:

```
package com.my.api

...

@Service

public class MappingsApiImpl implements MappingsApiDelegate {

    public ResponseEntity<APIMappedEntity> getMappings(String mappingType) {
            ...
        return ResponseEntity.ok(apiMappedEntity);
    }
}
```

The ```apiMappedEntity``` Objects were also generated out of the OpenAPI specification of the response objects.

Once you generate the code, the APIs also show up in the JHipster generated Swagger Documentation.