[BUG] [Java]: webclient: Error in the reactive client when the path variables are a list

[jorgerod]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
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Description

Error in the reactive client when the variables are a list.

openapi-generator version

4.2.2

OpenAPI declaration file content or url

openapi: 3.0.2
info:
  title: My-api
  version: 0.1.0
paths:
  /search/{ids}:
    get:
      summary: Find articles by article ids
      description: Retrieve articles from their ids.
      operationId: articles
      parameters:
        - name: ids
          description: article ids separated by commas
          in: path
          required: true
          schema:
            type: array
            items:
              type: integer
      responses:
        '200':
          description: OK

Command line used for generation

java -jar openapi-generator-cli.jar generate -g java -i openapi-rest.yml -o openapi --library resttemplate

Steps to reproduce

Run the above command and execute this test:

    @Test
    public void testListIntegers() {
        final ArrayList<Integer> ids = new ArrayList<>();
        ids.add(1);
        ids.add(2);

        Assert.assertNotNull(searchApi.findByIds(ids).block());
    }

Actual:

org.springframework.web.method.annotation.MethodArgumentTypeMismatchException: Failed to convert value of type 'java.lang.String' to required type 'java.util.List'; nested exception is java.lang.NumberFormatException: For input string: "[1,2]"
	at org.springframework.web.method.annotation.AbstractNamedValueMethodArgumentResolver.resolveArgument(AbstractNamedValueMethodArgumentResolver.java:133)
	at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:127)
	at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:167)
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:134)
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:893)
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:798)
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)

Expected
Request: GET: /search/1,2

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