Generate JSON schema from Java class
One such tool is Jackson JSON Schema module:
https://github.com/FasterXML/jackson-module-jsonSchema
which uses Jackson databind's POJO introspection to traverse POJO properties, taking into account Jackson annotations, and produces a JSON Schema object, which may then be serialized as JSON or used for other purposes.
Java JSON Schema Generator: https://github.com/victools/jsonschema-generator
Creates JSON Schema (Draft 6, Draft 7 or Draft 2019-09) from Java classes using Jackson.