[BUG] Dependency conflict (usage of swagger-annotations 1.6.8 and 2.2.4) leads to broken build

Description

Since openapi-generator 6.3.0 we're not able to build our project anymore. The reason therefore is that the generated classes from openapi-generator are generating methods with annotations like @Schema(name = "attr", requiredMode = Schema.RequiredMode.NOT_REQUIRED). The Schema.RequiredMode cannot be resolved properly because there are two versions of the same dependency in the classpath, both are used by the openapi-generator itself.

[INFO] +- org.openapitools:openapi-generator:jar:6.3.0:compile
[INFO] |  +- io.swagger.parser.v3:swagger-parser:jar:2.1.6:compile
[INFO] |  |  +- io.swagger.parser.v3:swagger-parser-v2-converter:jar:2.1.6:compile
[INFO] |  |  |  +- io.swagger:swagger-core:jar:1.6.8:compile
[INFO] |  |  |  |  +- io.swagger:swagger-models:jar:1.6.8:compile
[INFO] |  |  |  |  |  \- io.swagger:swagger-annotations:jar:1.6.8:compile
[INFO] |  |  \- io.swagger.parser.v3:swagger-parser-v3:jar:2.1.6:compile
[INFO] |  |     +- io.swagger.core.v3:swagger-core:jar:2.2.4:compile
[INFO] |  |     |  +- io.swagger.core.v3:swagger-annotations:jar:2.2.4:compile

The problem still persists in openapi-generator 6.4.0.

openapi-generator version

• 6.3.0
• 6.4.0

OpenAPI declaration file content or url

No specific API delcaration, since the problem is a dependency problem.

Generation Details

We use the Maven plugin for code generation from an OpenAPI spec. The corresponding config:

<configuration>
  <inputSpec>${project.basedir}/../myapp/openapi.yaml</inputSpec>
  <generatorName>spring</generatorName>
  <generateSupportingFiles>false</generateSupportingFiles>
  <modelPackage>com.company.mysoftware</modelPackage>
  <skipValidateSpec>true</skipValidateSpec>
  <configOptions>
    <sourceFolder>src/gen/java/main</sourceFolder>
    <reactive>true</reactive>
  </configOptions>
</configuration>

Steps to reproduce

Build the classes with Maven generator.

Related issues/PRs

None.

Suggest a fix

Use the same version of the dependency io.swagger.core.v3:swagger-annotations to prevent the classloader from dependency conflicts.

Start with the Maven plugin configuration and the dependency tree shown in the issue, focusing on the swagger-parser and swagger-annotations versions used by openapi-generator. Reproduce the Maven build with the Spring generator; done means the generated classes compile without conflicting Swagger annotation versions.