How do I register a HandlerInterceptor with constructor dependencies in Spring Boot - spring-mvc

Question

My use case is running custom code before a controller method by annotating methods.
HandlerInterceptor seems the way to go but it seems impossible to inject dependencies into it because it needs to be registered before the context is being created.
All examples I've found so far use empty constructors (see spring boot adding http request interceptors) or autowire properties in the configuration which fails because I declare dependent beans in the same configuration (Requested bean is currently in creation: Is there an unresolvable circular reference?).
Is there a better way that does not involve AOP?

Answer 1

Assume that your interceptor has constructor dependencies like that:
public class CustomInterceptor extends HandlerInterceptor {
private final DependentBean bean;
public CustomInterceptor(DependentBean bean) {
this.bean = bean;
}
}
Then you can register your handler like that:
#Configuration
public WebConfig extends WebMvcConfigurerAdapater {
#Bean
public DependentBean dependentBean() {
return new DependentBean();
}
#Bean
public CustomInterceptor customInterceptor() {
return new CustomInterceptor(dependentBean());
}
#Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(customInterceptor());
}
}
#Configuration will ensure each Bean method call return the same bean instance

Answer 2

Building on the answer above from Mạnh, if using component scan for dependency injection of the dependency, then that can be Autowired in the WebConfig
#Configuration
public WebConfig extends WebMvcConfigurerAdapater {
#Autowired
DependentBean dependentBean;
#Bean
public CustomInterceptor customInterceptor() {
return new CustomInterceptor(dependentBean);
}
#Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(customInterceptor());
}
}

Answer 3

Also building on previous answers, and if you use Lombok, you can further simplify.
Have your interceptor implementation been a #Component
Add a private final DependentBean field to it.
Also add a #RequiredArgsConstructor annotation to it, to have Lombok generating a constructor with a single DependentBean parameter.
In your WebConfig, use the same technic to have a private final CustomInterceptor field been injected by Spring IOC.
This way the CustomInterceptor instance will be available & initialized the right way when addInterceptors will be called
Here are the corresponding code samples :
The CustomInterceptor :
#Component
#RequiredArgsConstructor
public class CustomInterceptor implements HandlerInterceptor {
private final DependentBean dependentBean;
#Override
public boolean preHandle( final HttpServletRequest request,
final HttpServletResponse response,
final Object handler ) throws Exception {
// your Interceptor Implementation goes here ...
}
}
The WebConfig :
#Configuration
#RequiredArgsConstructor
public class WebConfig implements WebMvcConfigurer {
private final CustomInterceptor customInterceptor;
#Override
public void addInterceptors( final InterceptorRegistry registry ) {
registry.addInterceptor( customInterceptor );
}
}