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Behind the scenes

The following paragraphs describe how springwolf works internally.

Big Picture​

When the Spring Boot application is started, springwolf uses its scanners to find defined consumers and producers within the application. Based on the results, the channels/topics are extracted including payload type and merged together into an AsyncApi conform document.

The AsyncApi document is accessible an endpoint. When the springwolf ui is opened, the browser fetches the document and renders it (see demo).

When publishing is enabled, the user can publish a message through the ui to another endpoint. From there, springwolf forwards the message to the protocol specific producer.

Plugins​

springwolf-core provides the base functionality to orchestrate the scanning and building of the AsyncApi document. The different protocol (AMQP, Kafka) are supported through plugins. These plugins are found through the Spring dependency injection functionality. When building own scanner plugins, your plugin will need to implement the ChannelsScanner interface.

Scanners​

springwolf-core runs all scanners and merges the found results together into one AsyncApi document. When the same channel/topic is found multiple times, it is merged as well.

The result is a ChannelItem. The ChannelItem contains the Message for the subscribe and/or publish operation.

Building an example payload​

When the scanners scan and build the result, they also extract the payload type. The payload is registered in the SchemasService, which allows to split the Message from the schema definition - within the AsyncApi doc a $ref references is used.

Using swagger-inflector any class can be converted into a OpenApi schema. This is used to instantiate an Example object with default values and serialized into an example json for the AsyncApi document.

By using swagger-inflector, all the @Schema and other swagger annotations are supported as well as @JsonProperty through the use of the objectmapper.

ModelConverters​

ModelConverters provide a way to improve documentation for classes, which cannot be modified, for example because they are part of an external library. They follow the same plugin model.

Putting it all together​

The AsyncApiService collects all the channels, schemas and general info and builds the AsyncApi document. The controller access this services to serve the document to the ui.