[BUG][JAVA] ApiClient.basePath doesnt respect relative urls as described in the openapi definition

[thmsckldt]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
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Description

The generator prefixes the basePath variable in class ApiClient with "http://localhost" when servers[0].url == '/api-xyz'
resulting in a basePath == 'http://localhost/api-xyz'

The expected basePath is '/api-xyz'

openapi-generator version

7.2.0

OpenAPI declaration file content or url

openapi: "3.0.3"
info: 
  title: "test api"
  version: v1
servers: 
  - url: "/api-xyz"
paths: 
 "/account/v1/json/login":
    post: 
      responses:
        '201':
          description: Created
      requestBody: 
        description: ""
        content: 
          "application/json": 
            schema: 
              type: object
              properties: 
                emailAddress: 
                  type: string
                password: 
                  type: string

Related issues/PRs

#10056

Suggest a fix

The regex used in

openapi-generator/modules/openapi-generator/src/main/java/org/openapitools/codegen/utils/URLPathUtils.java

Line 238 in e69fb86

return Pattern.matches("^(\\/[\\w\\d]+)+", firstServer.getUrl());

doesnt allow special characters in relative paths.

Suggestion: ^(\/[\w\d_-]+)+
(will allow "-" and "_" in relative paths)

[humbleCraftman]

Will be fixed in 7.20.0 by #22768