Hi,
I am summarizing here your requirements to make sure I got them right:
1. to generate open api specification programmatically / manipulate/write Open API Specification
2. manipulating and generating an Open API Spec yaml
3. java code generated SDK from the Open API specification schema / SDK of java POJOs that supports the full extent the Open API Spec schema
This functionality is provided by one or more of swagger-api OSS tools, specifically:
Swagger Core (see also wiki ) provides OAS Java Representation, APIs, (de)serialization, resolution from POJOs / JAX-RS and annotations.
Swagger Parser provides parsing/validation and dereferencing/bundling
Swagger Codegen provides generation from a OAS spec of client SDKs and Server stubs in various languages including JAVA, and of documentation.
Also check Web/JS tools Swagger UI (here a demo) for rendering/visualization/testing and web editors Swagger Editor (here a demo, supports OAS 2.x and 3.0) and Swagger Editor@Next (here a demo, supports OAS 3.0-3.1 and AsyncAPI 2.x)
