spring-openapi (OpenAPI 3 generator)

Java CI

Spring Boot OpenAPI 3 generator. It scans provided packages (model and controller) and generates based on reflection, javax validation and spring annotations the OpenAPI 3 json. It is able to handle also inheritance using OpenAPI 3 discriminator possibilities. The inheritance generation is achieved using jackson annotations.

Generator allows you to also intercept schema, schema field, operation and operation parameter process, so you can include your own behavior to enrich already mapped sections (e.g. include own annotation behavior to descriptions etc.).

So far there is core generator functionality spring-openapi-schema-generator and maven plugin spring-openapi-schema-generator-plugin available.Soon there will be also java client generator finalized, because current tooling is still not able to generate client with full OpenAPI 3 discriminator features (jackson annotations).

There is also short article describing usage of spring-openapi generator here: https://medium.com/@remenec.jakub/openapi-3-spec-and-client-generation-on-java-spring-application-38a9ba5a2932.

Current version


Now generator supports also OpenAPI version 2 generation.

Release notes: https://github.com/jrcodeza/spring-openapi/blob/master/CHANGELOG.md

1.2.1 - to ensure compatiblity with swagger ui for bigger inheritance structures. This version models inheritance using allOf only if discriminator (JsonSubTypes) is found in inheritance hierarchy. If not, it takes all attributes from parent classes and adds them to the current one. See tests for more info.

Example project

You can check this repository https://github.com/jrcodeza/spring-openapi-example for an example usage. It shows spec to code and also code to spec generation using maven plugins. It contains simple REST resources, model (including inheritance), interceptors and examples resolver.

OpenAPI UI interpreter

If you need to display OpenAPI v3 spec in browser you can have a look also on oas-ui plugin https://github.com/vahanito/oas-ui (which was developed together with spring-openapi) . It supports searching of components and resources. Correctly displays inheritance also with discriminator info. You can use it in react as plugin or also as standalone bundle js.



You can define it on class, method, parameter or field. There are 2 main use cases:


The **exampleKey** parameter is a key for which example value should be provided by resolver. It can be 
for example a file name with example request - then goal of the resolver is to read file content and provide

It's possible to define more examples for one element by wrapping @OpenApiExample annotation to **@OpenApiExamples**
one. Name of the example becomes important in this case, because it will be stored to spec as example name.

### @OpenApiIgnore
Element annotated with this annotation will not be generated to spec.

### @Response
Sometimes you need to specify method (operation) response in your own way. It can 
be necessary when you have several return statuses or response types. Also when 
you want to specify response headers. For this purpose you can use this annotation.

It's also possible to wrap multiple @Response annotations to **@Responses** annotations. E.g.:
    @Response(responseCode = 201, description = "Created", responseBody = ValidationDummy.class,
            headers = @Header(name = "SomeHeader", description = "TestHeader")),
    @Response(responseCode = 200, description = "Replaced", responseBody = ValidationDummy.class)

@Header annotation is also custom spring-openapi annotation.

Generate spec from code

Runtime usage

Include dependency


Instantiate OpenAPIGenerator

OpenAPIGenerator openAPIGenerator = new OpenAPIGenerator(

The first parameter is model package and the second is controller package. It is possible to define multiple packages for each. The third parameter is OpenAPI basic info like project title, description, version etc. It is required in order to create valid OpenAPI 3 output. Additionally you can define interceptors

You can add these interceptors either to constructor after info parameter or by calling add + interceptorName method on OpenAPIGenerator class. E.g.:


You can define your own interceptor as follows:

package com.github.jrcodeza.schema.generator.plugin.interceptors;

import java.lang.reflect.Method;

import com.github.jrcodeza.schema.generator.interceptors.OperationInterceptor;

import io.swagger.v3.oas.models.Operation;

public class TestOperationInterceptor implements OperationInterceptor {

    public void intercept(Method method, Operation transformedOperation) {
        transformedOperation.setSummary("Interceptor summary");


It's possible to define also global headers which are applicable for all resources.

openAPIGenerator.addGlobalHeader("Test-Global-Header", "Some desc", false);

OpenAPIGenerator method generate can also take OpenApiGeneratorConfig as parameter. In this config you can define if generation of examples is enabled. You can also define example resolver, which can be useful if for example you have bigger examples of POST body requests stored in files. You can define it as follows:


Finally when you want to generate OpenAPI 3 spec you have to execute generate method on OpenAPIGenerator instance.

OpenAPI openAPI = openAPIGenerator.generate();

and you will receive OpenAPI object (from swagger API) which can be serialized to string like this

ObjectMapper objectMapper = new ObjectMapper();
try {
    String generated = objectMapper.writeValueAsString(openAPI);
    JSONAssert.assertEquals(getResourceFileAsString(), generated, false);
} catch (JsonProcessingException | JSONException e) {

Maven plugin usage

Maven plugin wraps before mentioned functionality into maven plugin.

                <title>Test title</title>
                <description>Test description</description>

You can see that title, description and version are the OpenAPI info parameters. Then you have to define also modelPackages and controllerPackages. Additionally you should define also outputDirectory, in our case target/openapi will be the target folder where the swagger.json will be saved.

From 1.2.0 version it is also possible to define all interceptors also in plugin. Additionally there is also option to turn on/off generateExamples and of course specify openApiExamplesResolver.

Generate client from spec

Runtime usage

Include dependency


Use generator in code

new OpenApiClientGenerator().generateClient(
                "targetFolder", // e.g. /target/generatedSources/oas
                true); // should generate interface

Maven plugin usage

  1. Include dependency

  2. Add plugin to maven plugins section


    generateResourceInterface option allows you to turn on/off generation of interface with methods that represent operations of the API.

generateDiscriminatorProperty allows you to turn on/off functionality where plugin generates the discriminator property explicitly to class (setting it visible=true in jackson). This is handy when you need to see the discriminator property inside the class and being able to access it using setter or getter.


Pull requests are welcome. If you would like to collaborate more feel free to contact me on [email protected] .


License for this tool is GNU GPL V3.