It's very good for basic introduction to Rest API. Thank you. It was exactly the lecture I wanted. When Swagger is added in SpringBoot2.2 or higher, a HATEOS usage error occurs. I wonder if there are people who struggle like me... NoUniqueBeanDefinitionException occurs Solution: Add the following to the Swagger configuration file class. @Primary @Bean public LinkDiscoverers discoverers() { List<LinkDiscoverer> plugins = new ArrayList<>(); plugins.add(new CollectionJsonLinkDiscoverer()); return new LinkDiscoverers(SimplePluginRegistry.create(plugins)); }