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Frequently Asked Questions

General​

Is Springwolf free & What's the license​

Yes, you can use Springwolf for private and commercial purposes as long as you comply to the Apache License 2.0.

Use springwolf-ui only (without plugins)​

You can use springwolf-ui without any other Springwolf dependency. springwolf-ui will fetch any documentation available at the springwolf/docs path. It must be in json format (yaml isn't supported).

Either create a custom spring controller to serve the file or serve static resources with spring and place AsyncAPI document file called docs (without file extension) into the folder resources/springwolf.

Note: springwolf-ui doesn't support the full AsyncAPI spec.

Unit test verification​

With the AsyncAPI artifact checked into the repository at src/test/resources/asyncapi.json, a unit test can verify that the current code still matches the expected AsyncAPI specification. Additionally, a diff reveals (un)expected changes.

Example unit test:

@SpringBootTest(
     classes = {SpringwolfKafkaExampleApplication.class},
     webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
class ApiIntegrationTest {

    @Autowired
    private TestRestTemplate restTemplate;

    @Test
    void asyncApiResourceArtifactTest() throws IOException {
        String url = "/springwolf/docs";
        String actual = restTemplate.getForObject(url, String.class);
       
        // writing the actual file can be useful for debugging (remember: gitignore)
        Files.writeString(Path.of("src", "test", "resources", "asyncapi.actual.json"), actual);

        InputStream s = this.getClass().getResourceAsStream("/asyncapi.json");
        String expected = new String(s.readAllBytes(), StandardCharsets.UTF_8).trim();

        assertEquals(expected, actual);
    }
}

For a full example, check the springwolf-kafka-example ApiIntegrationTest

Troubleshooting​

Show debug output in the logs​

Springwolf uses the default logging setup of Spring Boot. To enable DEBUG output, add the following line to the application.properties:

logging.level.io.github.springwolf=DEBUG

The Springwolf UI isn't showing​

When the springwolf-ui dependency is added, the UI should be visible at http://localhost:8080/springwolf/asyncapi-ui.html.

If not, whether

  1. you customized the spring context-path setting

  2. static assets are being served at all. See the code below:

    @Configuration
    public class WebConfig implements WebMvcConfigurer {
       @Override
       public void addResourceHandlers(ResourceHandlerRegistry registry) {
         registry
             .addResourceHandler("/**")
             .addResourceLocations("classpath:/META-INF/resources/", "classpath:/resources/", "classpath:/static/", "classpath:/public/");
       }
    }

    Taken from Discord Chat

  3. spring-security (or similar) denies access the URLs (HTTP 403). Check CustomWebSecurityConfigurerAdapter in springwolf-kafka-example.

Unable to publish message from the UI​

Publishing messages from the UI is disabled by default due to security concerns. Springwolf doesn't offer authentication nor authorization, anyone can publish messages to (production) channels.

Check the configuration to enable this feature. Be sure to enable fully qualified names (use-fqn) as well.

Spring Security allows to limit access to authorized users.

Consumers are detected multiple times (with different payloads)​

When Springwolf finds multiple consumers/producers for the same channel/topic, these are merged together. This is expected, as there are use-cases where different payloads are sent via the same channel/topic.

Springwolf uses on scanners to find all consumer and producers in your application. Most likely two scanners found your consumer/producer each. See configuration to disable scanners.

Only one of multiple classes with the same name (different package) is detected​

Enable the fully qualified class name (FQN) option (springwolf.use-fqn=true) so that Springwolf uses the FQN internally.

Generic types (List) don't contain item properties​

Due to java type erasure some generic type information is lost during runtime.

Defining your own type can resolve this.

Change

public void sendMessage(List<String> msg) {}

to

class ListWrapper extends ArrayList<String> {}

public void sendMessage(ListWrapper<String> msg) {}

Release Notes / Migration Guide / Updating / Upgrading​

Releases are managed in GitHub Releases, which feature noteworthy changes, the full changelog and notes on how to migrate.

Since each release has a git tag, the Springwolf examples for each plugin showcase the use of Springwolf for any previous version.

How to migrate from Springwolf 0.18.0 to 1.0.0​

See Release 1.0.0.

How to migrate from the deprecated AsyncApiDocket bean to Spring properties​

See Issue #445.

Is Spring Boot 2.X supported​

You can use an older version of Springwolf, which is build to support Spring Boot 2.X. However, these versions don't get any updates.

Last versions to support Spring Boot 2.X:

  • springwolf-amqp:0.6.0
  • springwolf-cloud-stream:0.1.0
  • springwolf-core:0.6.0
  • springwolf-kafka:0.10.0
  • springwolf-ui:0.6.0

Usage Patterns​

How to access the generated documentation within java​

Use the AsyncApiService to access the generated documentation.

How to generate the documentation at build time​

With Gradle​

You can use the springdoc-openapi-gradle-plugin and configure the plugin for Springwolf by pointing it to the Springwolf docs endpoint:

openApi {
    apiDocsUrl = "http://localhost:8080/springwolf/docs"
    outputDir = file("$buildDir/docs")
    outputFileName = "async-api.json"
}

The springwolf-kafka-example contains a working example.

The plugin will startup the spring boot application by using the bootRun task and then try to download the documentation from the given apiDocsUrl and store it in the outputDir and with the given outputFileName.

If your application is unable to start up with the bootRun task, see if customBootRun properties can help you.