[JAVA] etc.: generated code is incorrect for untyped schemas

[gibson042]

Description

Generated code for schemas with no defined type is incorrect, because parsing seems to require a type property despite it being optional in the specification (where it defines values that can be of any type).

Swagger-codegen version

2.2.3, 2.3.0-SNAPSHOT

Swagger declaration file content or url

swagger: '2.0'
info:
  title: 'map of arbitrary values'
  version: '1'
produces: ["application/json"]
paths:
  /mapOfAnything:
    get:
      operationId: mapOfAnything
      responses:
        default:
          schema:
            description: 'map of arbitrary values'
            type: object
            additionalProperties:
              description: Any JSON type

Command line used for generation

./run-in-docker.sh generate -i swagger.yaml -l java

Steps to reproduce

Generate code from the above YAML. Observe that the response is treated as Object instead of Map<String, Object>, despite describing a map.

Related issues/PRs

None found.

Suggest a fix/enhancement

Treat untyped schemas as generically as possible.

[n0v1]

We have the same problem with Java CodeGen and additionalProperties without a specific type. We have a meta field in our response structure that may contain arbitrary properties. So, ideally we'd like to use something like that

swagger: "2.0"

info:
  version: "1.0.0"
  title: "Test"

paths:
  /test:
    get:
      description: "Test request"
      responses:
        200:
          description: "Successful operation"
          schema:
            $ref: "#/definitions/Meta"

definitions:
  Meta:
    description: Key value map for meta data.
    type: object
    additionalProperties: {}

to make it explicit that there are no restrictions on the type of additional properties. With that the Meta class is of type Object (public class Meta), but should be HashMap<String, Object> (public class Meta extends HashMap<String, Object>)

As a hack to work around this issue, we use

additionalProperties:
  type: object

This fixes the problem with Java CodeGen but leads to validation errors when validating our response data since most meta properties are simple types like strings and integers instead ob objects.

I would be great if the pull requests from @gibson042 could get merged to fix this problem.