[JAVA] generator cannot handle use of allOf or $ref for defined simple types

Description

When I define a common simple type like for example:

definitions:
...
  Guid:
    type: string
    format: guid
    pattern: '^[0-9A-Fa-f]{8}(-[0-9A-Fa-f]{4}){3}-[0-9A-Fa-f]{12}$'
    description: |
      A guid identifier. No value can be set as "000000000-0000-0000-0000-00000000000".
    example: '5e0fe30e-3724-42c2-b5b9-0b1594b0b7a3'
    x-example: "5e0fe30e-3724-42c2-b5b9-0b1594b0b7a3"

And then I use this type as follows in a defined object type:

  MyObjectType:
    type: object
    required:
      - id
    properties:
      id:
        description: |
          the id of the object
        allOf:
          - $ref: "#/definitions/Guid"

or even...

  MyObjectType:
    type: object
    required:
      - id
    properties:
      id:
        $ref: "#/definitions/Guid"

Then the generated code is not correct.
In the first case the property "id" is simply missing from the "MyObjectType" class.
And in the second case the property is added as a class object property of Class type "Guid"

public class MyObjectType{

  @JsonProperty("id")
  private Guid id= null;

but the class "Guid" does not exist, and its should be a String.

This is they way to define commonly used simple types in Swagger.
Could the generator be changed to be able to handle this?

Swagger-codegen version

v2.2.3

Swagger declaration file content or url

Command line used for generation

        main = 'io.swagger.codegen.SwaggerCodegen'
        args = ["generate",
                "-l", "java",                                                       // language
                "-i", "${project.ext.inputDir}${version}/${project.ext.inputFile}", // input
                "-c", configJson.getAbsolutePath(),                                 // config
                "-o", "${project.ext.sourceset}",                                   // output
        ]
        jvmArgs = ['-Dmodels']                                                      // generate models only

Steps to reproduce

Related issues/PRs

Suggest a fix/enhancement

When handling a "$ref" or "allOf" reference the type (object, string,...) of the referenced type should be take into account. So not always a class (object) reference is assumed.

Start by reproducing the Java model-only generation command with the provided Guid and MyObjectType definitions. Trace how the generator resolves $ref and allOf for model properties. Done means the id property is generated as a String in MyObjectType for both forms, without generating or referencing a Guid class.