How to do it...

Despite what you might think, after seeing the previous recipe, adding an interceptor is not as straightforward as just declaring it as a bean. We actually need to do it via WebMvcConfigurer or by overriding WebMvcConfigurationSupport. Let's take a look at the following steps:

1. Let's enhance our WebConfiguration class to implement WebMvcConfigurer:

public class WebConfiguration implements WebMvcConfigurer {...} 

1. Now we will add a @Bean declaration for LocaleChangeInterceptor:

@Bean 
public LocaleChangeInterceptor localeChangeInterceptor() { 
  return new LocaleChangeInterceptor(); 
} 

1. This will actually create the interceptor Spring bean, but will not add it to the request handling chain. For this to happen, we will need to override the addInterceptors method and add our interceptor to the provided registry:

@Override 
public void addInterceptors(InterceptorRegistry registry) { 
  registry.addInterceptor(localeChangeInterceptor()); 
} 

1. Start the application by running ./gradlew clean bootRun
2. In the browser, go to http://localhost:8080/books?locale=foo
3. Now, if you look at the console logs, you will see a bunch of stack trace errors basically saying the following:

Caused by: java.lang.UnsupportedOperationException: Cannot change HTTP accept header - use a different locale resolution strategy