Generate Java Spring API from OpenAPI 3

Question

I tried to generate Spring REST interfaces from OpenAPI v3 YAML file. Build says:

Successfully generated code to property(class java.lang.String, property(class java.lang.String, fixed(class java.lang.String, /home/zolv/workspaces/main/generation-test/src/main/java)))

Deprecated Gradle features were used in this build, making it 
incompatible with Gradle 6.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/5.5/userguide/command_line_interface.html#sec:command_line_warnings

But there is no code generated in output directory.

I followed OpenAPI generator gradle plugin doc doc.

My build.gradle:

plugins {
  id 'java-library'
  id "org.openapi.generator" version "4.1.1"
}

repositories {
  jcenter()
}

dependencies {
    implementation "org.openapitools:openapi-generator-gradle-plugin:3.3.4"
}

openApiGenerate {
  generatorName = "spring"
  inputSpec = "$rootDir/docs/openapi/api.yml".toString()
  outputDir = "$rootDir/src/main/java".toString()
  apiPackage = "org.openapi.example.api"
  invokerPackage = "org.openapi.example.invoker"
  modelPackage = "org.openapi.example.model"
  modelFilesConstrainedTo = [
          "Error"
  ]
  configOptions = [
      dateLibrary: "java8"
  ]
}

My api.yml:

openapi: 3.0.2
info:
  title: API Documentation
  version: 1.0.0
servers:
  - url: http://localhost:8080/
tags:
  - name: Users
paths:
  /users:
    post:
      tags:
        - Users
      summary: Create user
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/CreateUserRequest'
      responses:
        201:
          description: New user created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/UserResponse'
components:
  schemas:
    CreateUserRequest:
      title: CreateUserResponse
      required:
        - username
        - password
      type: object
      properties:
        username:
          type: string
          description: Users's username
          example: [email protected]
        password:
          type: string
          description: User's password
          example: $tR0nG_pA55vv0Rd
    UserResponse:
      title: UserResponse
      required:
        - id
        - username
      type: object
      properties:
        id:
          type: string
          description: Users's identifier
          example: "1"
        username:
          type: string
          description: Users's username
          example: [email protected]

api.yml is properly gathered by generator (Build fails if there are any syntax errors in the file).

It looks suspicious that build logs say: Successfully generated code to property(.... Doesn't mean the property contains the result of generation ?

Gradle version:

------------------------------------------------------------
Gradle 5.5
------------------------------------------------------------

Build time:   2019-06-28 17:36:05 UTC
Revision:     83820928f3ada1a3a1dbd9a6c0d47eb3f199378f

Kotlin:       1.3.31
Groovy:       2.5.4
Ant:          Apache Ant(TM) version 1.9.14 compiled on March 12 2019
JVM:          11.0.4 (Ubuntu 11.0.4+11-post-Ubuntu-1ubuntu218.04.3)
OS:           Linux 4.15.0-1050-oem amd64

Edit:

I've checked example from gradle plugin, and code above works with Gradle v4, but not with 5. I'm still investigating.

Solution

The problem seems to be in modelFilesConstrainedTo — it limits the classes to Error. Comment it out and it will work (classes will be generated).

However, there is another problem: outputDir. With your setting it will generate something like:

That's wrong. Also, as it is a generated source, it should not go to src/main. A better alternative is to generate it in build directory and then add it to the compilation classpath. Take a look at the demo project I've create for you, and here is the build.gradle.kts (it's almost like Groovy):

plugins {
    id("java-library")
    id("org.openapi.generator").version("4.0.1")
    id("org.springframework.boot").version("2.1.8.RELEASE")
}

repositories {
    jcenter()
}

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-web:2.1.8.RELEASE")
    api("io.springfox:springfox-swagger2:2.8.0")
    api("io.springfox:springfox-swagger-ui:2.8.0")
    api("org.openapitools:jackson-databind-nullable:0.1.0")
}

val spec = "$rootDir/docs/openapi/api.yml"
val generatedSourcesDir = "$buildDir/generated/openapi"

openApiGenerate {
    generatorName.set("spring")

    inputSpec.set(spec)
    outputDir.set(generatedSourcesDir)

    apiPackage.set("org.openapi.example.api")
    invokerPackage.set("org.openapi.example.invoker")
    modelPackage.set("org.openapi.example.model")

    configOptions.set(mapOf(
            "dateLibrary" to "java8"
    ))
}

sourceSets {
    getByName("main") {
        java {
            srcDir("$generatedSourcesDir/src/main/java")
        }
    }
}

tasks {
    val openApiGenerate by getting

    val compileJava by getting {
        dependsOn(openApiGenerate)
    }
}

Note that you'll also need a bunch of dependencies that are used in generated sources (annotations and Spring classes).

Comments

[zolv]

Thank You for Your very verbose answer! Generation output set as java/main was just for a test to be sure that I don't have a problem with missing directory. As it finaly started working, I noticed that it generates the whole project instead of just a Spring code (as I was expecting). I need to dig through documentation now, I hope there is some kind of switch to disable this. Thank You!

[Shmarkus]

For me, the modelFilesConstrainedTo removal did the trick, thanks