[Java] Add proper support for allOf anyOf oneOf

Created by: MarvGilb

Description

In the openApiSpec it is possible to define a schema with properties, where one property can be defined directly or be using oneOf anyOf or allOf and passing the some provided Schemas.

Currently only allOf is considered and only the first of these schemas is taken (allOf requires all of them!). The other two delimiter are not even considered.

The following example makes it only possible to set the CustomProperties.

openapi-generator version

3.1.1

OpenAPI declaration file content or url

Sample Snippet.:

info:
  title: test
  version: 1.0.0
paths:
  /test:
    get:
      responses:
        '200':
          description: All good
          content:
            '*/*':
              schema:
                $ref: '#/components/schemas/ObjectWithProps'
      operationId: get
      summary: Get object with properties.
components:
  schemas:
    ObjectWithProps:
      properties:
        properties:
          allOf:
           - $ref: '#/components/schemas/CustomProperties'
           - $ref: '#/components/schemas/Properties'
      description: An object with difined and undifined keys.
    CustomProperties:
      description: The custom properties key.
      type: object
      properties:
        'someDefinedKey':
          type: object
          additionalProperties:
            type: object
    Properties:
      description: The wildcard properties key.
      type: object
      additionalProperties:
        type: object
openapi: 3.0.0

Steps to reproduce

java -jar ${PathToOpenApiGeneratorJAR3.1.1} generate \
 -i /path/swagger3.yaml \
 -o /path/swagger3-client \
 --api-package "com.123" \
 --model-package "com.123" \
 --group-id "com.123" \
 --artifact-id "123" \
 --artifact-version "SNAPSHOT" \
 -c ./java-options.json \
 -g java

JavaOptions:

{
  "java8": true,
  "dateLibrary": "java8"
}