[BUG][Spring] Hateoas with Swagger bean resolution error

Created by: redturtlepower

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?
• [Optional] Bounty to sponsor the fix (example)

Description

If using hateoas config option this error occurs. A comment on SO here states there is an issue with swagger and hateos when used together. I found this springfox issue that highlights a solution. I tried this solution and it worked. The solution requires adding a bean resolution strategy (5 lines) + required imports (4 lines).

***************************
APPLICATION FAILED TO START
***************************

Description:

Parameter 0 of method linkDiscoverers in org.springframework.hateoas.config.HateoasConfiguration required a single bean, but 16 were found:
	- modelBuilderPluginRegistry: defined in null
	- modelPropertyBuilderPluginRegistry: defined in null
	- typeNameProviderPluginRegistry: defined in null
	- documentationPluginRegistry: defined in null
	- apiListingBuilderPluginRegistry: defined in null
	- operationBuilderPluginRegistry: defined in null
	- parameterBuilderPluginRegistry: defined in null
	- expandedParameterBuilderPluginRegistry: defined in null
	- resourceGroupingStrategyRegistry: defined in null
	- operationModelsProviderPluginRegistry: defined in null
	- defaultsProviderPluginRegistry: defined in null
	- pathDecoratorRegistry: defined in null
	- apiListingScannerPluginRegistry: defined in null
	- relProviderPluginRegistry: defined by method 'relProviderPluginRegistry' in class path resource [org/springframework/hateoas/config/HateoasConfiguration.class]
	- linkDiscovererRegistry: defined in null
	- entityLinksPluginRegistry: defined by method 'entityLinksPluginRegistry' in class path resource [org/springframework/hateoas/config/WebMvcEntityLinksConfiguration.class]


Action:

Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed

openapi-generator version

4.2.3

OpenAPI declaration file content or url

Command line used for generation

rmdir /q /s server\springboot\openapi
REM generate the server source code from the OpenAPI spec petstore.yaml:
java -jar openapi-generator-cli-4.2.3.jar generate -g spring -i petstore.yaml -o server\springboot\openapi -c springboot-options.json

file "springboot-options.json"

{
"basePackage":"io.swagger",
"configPackage":"io.swagger.config",
"parentGroupId":"org.springframework.boot",
"parentArtifactId":"spring-boot-starter-parent",
"parentVersion":"2.2.4.RELEASE",
"serverPort":9230,
"hateoas":true,
"delegatePattern":true
}

Steps to reproduce

Related issues/PRs

I didn't find one

Suggest a fix

The soluting code was manually added to generated file "OpenAPI2SpringBoot.java". Someone needs to update the mustache template accordingly.

import org.springframework.hateoas.client.LinkDiscoverer;
import org.springframework.http.MediaType;
import org.springframework.plugin.core.OrderAwarePluginRegistry;
import org.springframework.plugin.core.PluginRegistry;

@SpringBootApplication
@ComponentScan(basePackages = {"io.swagger", "org.openapitools.api" , "io.swagger.config"})
public class OpenAPI2SpringBoot implements CommandLineRunner {

   @Override
   public void run(String... arg0) throws Exception {
       if (arg0.length > 0 && arg0[0].equals("exitcode")) {
           throw new ExitException();
       }
   }

   // Uncomment to fix the issue with swagger and hateoas
   /* 
   @Bean
   public PluginRegistry<LinkDiscoverer, MediaType> discoverers(
           OrderAwarePluginRegistry<LinkDiscoverer, MediaType> relProviderPluginRegistry) {
       return relProviderPluginRegistry;
   }
   */