springdoc-openapi-scala

An enhancement to springdoc-openapi that adds better support for Scala.

Motivation

Scala isn't well-supported in springdoc-openapi by default, for example:

case class parameters are not recognized by default, one has to add something like @BeanProperty to each
even with @BeanProperty, most parameters with generic type (like Option) don't work correctly
even with @BeanProperty, all parameters are marked as not required in generated OpenAPI docs
Spring endpoints returning Unit are not "No Content" but instead show that the endpoint returns BoxedUnit

One option to overcome these limitations is to annotate the model with annotations provided by springdoc-openapi. But even with them, @BeanPropery or equivalent must be added to each case class parameter.

This library aims to avoid pollution of the model by custom annotations and dependency on Spring related libraries.

Features

all parameters of a case class are automatically recognized without any custom annotations
all parameters of a case class that have a type different from Option are marked as required
Spring endpoints returning Unit are "No Content"
support for basic Scala collections (Map, Seq, Set, Array) as types of case class parameters
only top-level case classes need to be registered, child case classes are then recursively registered
support for Scala Enumeration where simple Value constructor is used (without name)
support for sum ADTs (sealed trait and sealed abstract class) with optional discriminator

Usage

springdoc-openapi-scala supports two major versions of springdoc-openapi: 1.x and 2.x.

Provided dependencies

The library has springdoc-openapi as a provided dependency, thus users of the library have to include that dependency in their projects:

for springdoc-openapi 1.x versions 1.6.7 up to 1.7.0 (including) of "org.springdoc" % "springdoc-openapi-webmvc-core" are supported
for springdoc-openapi 2.x versions 2.0.0 onwards of "org.springdoc" % "springdoc-openapi-starter-webmvc-api" are supported

Add library dependency to SBT/Maven

SBT

If you want to use the library with springdoc-openapi 1.x, add:

libraryDependencies ++= Seq("za.co.absa" %% "springdoc-openapi-scala-1" % VERSION)

if with springdoc-openapi 2.x, add:

libraryDependencies ++= Seq("za.co.absa" %% "springdoc-openapi-scala-2" % VERSION)

Maven

If you want to use the library with springdoc-openapi 1.x, add:

<dependency>
   <groupId>za.co.absa</groupId>
   <artifactId>springdoc-openapi-scala-1_${scala_binary_version}</artifactId>
   <version>${version}</version>
</dependency>

if with springdoc-openapi 2.x, add:

<dependency>
   <groupId>za.co.absa</groupId>
   <artifactId>springdoc-openapi-scala-2_${scala_binary_version}</artifactId>
   <version>${version}</version>
</dependency>

where scala_binary_version is either 2.12 or 2.13.

Create custom OpenAPI Spring Configuration

For springdoc-openapi 1.x

import io.swagger.v3.oas.models.OpenAPI
import io.swagger.v3.oas.models.info.Info
import org.springdoc.core.customizers.OpenApiCustomiser
import org.springframework.context.annotation.{Bean, Configuration}

import za.co.absa.springdocopenapiscala.{Bundle, OpenAPIModelRegistration}

@Configuration
class OpenAPIConfiguration {

  private val springDocOpenAPIScalaBundle = new Bundle(
    Seq((openAPI: OpenAPI) =>
      openAPI.setInfo(
        new Info()
          .title("Example API with springdoc-openapi v1.x")
          .version("1.0.0")
      )
    )
  )

  @Bean
  def openAPICustomizer: OpenApiCustomiser = springDocOpenAPIScalaBundle.customizer

  @Bean
  def openAPIModelRegistration: OpenAPIModelRegistration = springDocOpenAPIScalaBundle.modelRegistration

}

For springdoc-openapi 2.x

import io.swagger.v3.oas.models.OpenAPI
import io.swagger.v3.oas.models.info.Info
import org.springdoc.core.customizers.OpenApiCustomizer
import org.springframework.context.annotation.{Bean, Configuration}

import za.co.absa.springdocopenapiscala.{Bundle, OpenAPIModelRegistration}

@Configuration
class OpenAPIConfiguration {

  private val springDocOpenAPIScalaBundle = new Bundle(
    Seq((openAPI: OpenAPI) =>
      openAPI.setInfo(
        new Info()
          .title("Example API with springdoc-openapi v2.x")
          .version("1.0.0")
      )
    )
  )

  @Bean
  def openAPICustomizer: OpenApiCustomizer = springDocOpenAPIScalaBundle.customizer

  @Bean
  def openAPIModelRegistration: OpenAPIModelRegistration = springDocOpenAPIScalaBundle.modelRegistration

}

Register top-level model case classes (for example in Controller)

Example model:

case class ExampleModelRequest(a: Int, b: String, c: Option[Int])

case class ExampleModelResponse(d: Seq[Int], e: Boolean)

can be registered for example in Controller:

@RestController
@RequestMapping(
  value = Array("/api/v1/example")
)
class ExampleController @Autowired()(openAPIModelRegistration: OpenAPIModelRegistration) {

  openAPIModelRegistration.register[ExampleModelRequest]()
  openAPIModelRegistration.register[ExampleModelResponse]()

  @PostMapping(
    value = Array("/some-endpoint"),
    produces = Array(MediaType.APPLICATION_JSON_VALUE)
  )
  def someEndpoint(@RequestBody body: ExampleModelRequest): CompletableFuture[ExampleModelResponse] = {
    ...
  }
  
}

Adding support for custom types

To add support for custom types (or overwrite handling of any type supported by the library) one can create a custom ExtraTypesHandler and provide it when creating a Bundle.

There are multiple ways to do so, the simplest is to use ExtraTypesHandling.simpleMapping, for example:

OpenAPIModelRegistration.ExtraTypesHandling.simpleMapping {
  case t if t =:= typeOf[JsValue] =>
    val schema = new Schema
    schema.setType("string")
    schema.setFormat("json")
    schema
}

This ExtraTypesHandler handles JsValue by mapping it to simple OpenAPI string type with json format.

But ExtraTypesHandler can also be much more powerful, for example:

case class CustomClassComplexChild(a: Option[Int])

class CustomClass(val complexChild: CustomClassComplexChild) {
  // these won't be included
  val meaningOfLife: Int = 42
  val alphabetHead: String = "abc"
}

...

val extraTypesHandler: ExtraTypesHandler = (tpe: Type) =>
  tpe match {
    case t if t =:= typeOf[CustomClass] =>
      val childTypesToBeResolvedByTheLibrary = Set(typeOf[CustomClassComplexChild])
      
      val handleFn: HandleFn = (resolvedChildTypes, context) => {
        val name = "CustomClass"
        val customClassComplexChildResolvedSchema = resolvedChildTypes(typeOf[CustomClassComplexChild])
        val schema = new Schema
        schema.addProperty("complexChild", customClassComplexChildResolvedSchema)
        context.components.addSchemas(name, schema)
        val schemaReference = new Schema
        schemaReference.set$ref(s"#/components/schemas/$name")
        schemaReference
      }
      
      (childTypesToBeResolvedByTheLibrary, handleFn)
  }

This ExtraTypesHandler handles CustomClass. CustomClass uses CustomClassComplexChild, so the handler requests the library to resolve its type (childTypesToBeResolvedByTheLibrary). This resolved type is available as input to HandleFn. Then, in handleFn, the handler creates a Schema object for CustomClass, adds it to Components so that it can be referenced by name CustomClass, and returns reference to that object.

Registration configuration

It is possible to further customize registration by providing custom RegistrationConfig to OpenAPIModelRegistration.

Example

val components = ...
val registration = OpenAPIModelRegistration(
  components,
  config = RegistrationConfig(
    OpenAPIModelRegistration.RegistrationConfig(
      sumADTsShape =
         // default values apply for discriminatorPropertyNameFn, addDiscriminatorPropertyOnlyToDirectChildren
         OpenAPIModelRegistration.RegistrationConfig.SumADTsShape.WithDiscriminator()
    )
  )
)

sumADTsShape

This config property sets how sum ADTs are registered. It has two possible values:

RegistrationConfig.SumADTsShape.WithoutDiscriminator - default option, doesn't add discriminators
RegistrationConfig.SumADTsShape.WithDiscriminator(discriminatorPropertyNameFn, addDiscriminatorPropertyOnlyToDirectChildren) - adds discriminator to sealed types schema, and also adds discriminator to sum ADTs elements properties; discriminator property name is customizable by discriminatorPropertyNameFn, by default it takes sealed type name, converts its first letter to lower case, and adds "Type" suffix, for example if sealed type name is Expression, the property name is expressionType; if addDiscriminatorPropertyOnlyToDirectChildren is false, discriminator property is added to all children, so for example in ADT = A | B | C; B = D | E discriminator of ADT would be added to A, C, D, E (D and E would have discriminator of B in addition to that) while with addDiscriminatorPropertyOnlyToDirectChildren set to true (default) it would be added only to A and C

Examples

Simple example for springdoc-openapi-scala-1

Can be found in this repo: link. It generates the following OpenAPI JSON doc:

{
  "openapi": "3.0.1",
  "info": {
    "title": "Example API with springdoc-openapi v1.x",
    "version": "1.0.0"
  },
  "servers": [
    {
      "url": "http://localhost:8080",
      "description": "Generated server url"
    }
  ],
  "paths": {
    "/api/v1/example/some-endpoint": {
      "post": {
        "tags": [
          "example-controller"
        ],
        "operationId": "someEndpoint",
        "requestBody": {
          "content": {
            "application/json": {
              "schema": {
                "$ref": "#/components/schemas/ExampleModelRequest"
              }
            }
          },
          "required": true
        },
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/ExampleModelResponse"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "IntLiteral": {
        "required": [
          "value"
        ],
        "properties": {
          "value": {
            "type": "string"
          }
        }
      },
      "StringLiteral": {
        "required": [
          "value"
        ],
        "properties": {
          "value": {
            "type": "string"
          }
        }
      },
      "Literal": {
        "oneOf": [
          {
            "$ref": "#/components/schemas/IntLiteral"
          },
          {
            "$ref": "#/components/schemas/StringLiteral"
          }
        ]
      },
      "Something": {},
      "Expression": {
        "oneOf": [
          {
            "$ref": "#/components/schemas/Literal"
          },
          {
            "$ref": "#/components/schemas/Something"
          }
        ]
      },
      "ExampleModelRequest": {
        "required": [
          "a",
          "b",
          "d",
          "e"
        ],
        "properties": {
          "a": {
            "type": "integer",
            "format": "int32"
          },
          "b": {
            "type": "string"
          },
          "c": {
            "type": "integer",
            "format": "int32"
          },
          "d": {
            "type": "string",
            "format": "json"
          },
          "e": {
            "$ref": "#/components/schemas/Expression"
          },
          "f": {
            "$ref": "#/components/schemas/Expression"
          }
        }
      },
      "ExampleModelResponse": {
        "required": [
          "d",
          "e"
        ],
        "properties": {
          "d": {
            "type": "array",
            "items": {
              "type": "integer",
              "format": "int32"
            }
          },
          "e": {
            "type": "boolean"
          }
        }
      }
    }
  }
}

Simple example for springdoc-openapi-scala-2