Cannot parse openapi spec with Plugin or even with built package - JsonParseException: Unrecognized token 'openapi'

[sadra]

Description

I've tried to generate Java codes based on an openapi spec, I installed the package in pom.xml and tried to generate the code but I've get the following error wich it can't recognize an openapi spec.

The interesting thing is, it works fine with brew version of swagger-codegen, but the plugin cannot recognize an openapi spec, I've also cloned the swagger-codegen and built the package and tried to run with java -jar swagger-codegen-cli ... but it also had the same error. Only brew version works!

Generator:

package com.example.demo;

import io.swagger.codegen.ClientOptInput;
import io.swagger.codegen.config.CodegenConfigurator;
import io.swagger.models.Swagger;
import io.swagger.parser.SwaggerParser;

import java.util.ArrayList;
import java.util.List;

import static io.swagger.codegen.config.CodegenConfiguratorUtils.*;

public class Gen2 {
    private List<String> systemProperties = new ArrayList<>();
    private List<String> instantiationTypes = new ArrayList<>();
    private List<String> importMappings = new ArrayList<>();
    private List<String> typeMappings = new ArrayList<>();
    private List<String> additionalProperties = new ArrayList<>();
    private List<String> languageSpecificPrimitives = new ArrayList<>();
    private List<String> reservedWordsMappings = new ArrayList<>();


    public void gen(){
        CodegenConfigurator configurator = new CodegenConfigurator();

        configurator.setLang("java");
        configurator.setInputSpec("src/main/resources/openapi.yml");
        configurator.setOutputDir("target/generated-sources/client");
        systemProperties.add("models");
        
        applySystemPropertiesKvpList(systemProperties, configurator);
        applyInstantiationTypesKvpList(instantiationTypes, configurator);
        applyImportMappingsKvpList(importMappings, configurator);
        applyTypeMappingsKvpList(typeMappings, configurator);
        applyAdditionalPropertiesKvpList(additionalProperties, configurator);
        applyLanguageSpecificPrimitivesCsvList(languageSpecificPrimitives, configurator);
        applyReservedWordsMappingsKvpList(reservedWordsMappings, configurator);
        final ClientOptInput clientOptInput = configurator.toClientOptInput();

       new DGen().opts(clientOptInput).generate();
    }
}

Error:

13:01:20.758 [main] ERROR i.s.parser.SwaggerCompatConverter - failed to read resource listing
com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'openapi': was expecting (JSON String, Number, Array, Object or token 'null', 'true' or 'false')
 at [Source: (String)"openapi: "3.0.0"
info:
  version: 1.0.0
  title: Swagger Petstore
  license:
    name: MIT
servers:
  - url: http://petstore.swagger.io/v1
paths:
  /pets:
    get:
      summary: List all pets
      operationId: listPets
      tags:
        - pets
      parameters:
        - name: limit
          in: query
          description: How many items to return at one time (max 100)
          required: false
          schema:
            type: integer
            maximum: 100
            format: int32
 "[truncated 2114 chars]; line: 1, column: 8]
	at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:2477)
	at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:760)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:3041)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._handleOddValue(ReaderBasedJsonParser.java:2082)
	at com.fasterxml.jackson.core.json.ReaderBasedJsonParser.nextToken(ReaderBasedJsonParser.java:808)
	at com.fasterxml.jackson.databind.ObjectMapper._readTreeAndClose(ObjectMapper.java:4854)
	at com.fasterxml.jackson.databind.ObjectMapper.readTree(ObjectMapper.java:3219)
	at io.swagger.parser.SwaggerCompatConverter.readResourceListing(SwaggerCompatConverter.java:210)
	at io.swagger.parser.SwaggerCompatConverter.read(SwaggerCompatConverter.java:123)
	at io.swagger.parser.SwaggerParser.read(SwaggerParser.java:105)
	at io.swagger.codegen.config.CodegenConfigurator.toClientOptInput(CodegenConfigurator.java:452)
	at com.example.demo.Gen2.gen(Gen2.java:38)
	at com.example.demo.DemoApplication.main(DemoApplication.java:7)

Swagger-codegen version

        <dependency>
            <groupId>io.swagger.codegen.v3</groupId>
            <artifactId>swagger-codegen-maven-plugin</artifactId>
            <version>3.0.50</version>
        </dependency>

Swagger declaration file content or url

openapi: "3.0.0"
info:
  version: 1.0.0
  title: Swagger Petstore
  license:
    name: MIT
servers:
  - url: http://petstore.swagger.io/v1
paths:
  /pets:
    get:
      summary: List all pets
      operationId: listPets
      tags:
        - pets
      parameters:
        - name: limit
          in: query
          description: How many items to return at one time (max 100)
          required: false
          schema:
            type: integer
            maximum: 100
            format: int32
      responses:
        '200':
          description: A paged array of pets
          headers:
            x-next:
              description: A link to the next page of responses
              schema:
                type: string
          content:
            application/json:    
              schema:
                $ref: "#/components/schemas/Pets"
        default:
          description: unexpected error
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Error"
    post:
      summary: Create a pet
      operationId: createPets
      tags:
        - pets
      responses:
        '201':
          description: Null response
        default:
          description: unexpected error
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Error"
  /pets/{petId}:
    get:
      summary: Info for a specific pet
      operationId: showPetById
      tags:
        - pets
      parameters:
        - name: petId
          in: path
          required: true
          description: The id of the pet to retrieve
          schema:
            type: string
      responses:
        '200':
          description: Expected response to a valid request
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Pet"
        default:
          description: unexpected error
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Error"
components:
  schemas:
    Pet:
      type: object
      required:
        - id
        - name
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string
        tag:
          type: string
    Pets:
      type: array
      maxItems: 100
      items:
        $ref: "#/components/schemas/Pet"
    Error:
      type: object
      required:
        - code
        - message
      properties:
        code:
          type: integer
          format: int32
        message:
          type: string