Can a Spring MVC @Bean inspect the HTTP Request?

I have a scenario where HTTP requests are received by a Spring application with a custom ContentType and a JSON payload. A piece of the payload is a key used in a service locator call.

Payload:

{ "service_id": "ServiceA" }

I'd like to use a @RequestScope'd Spring @Bean to inspect the request and return / inject the correct service.

Something like:

@Configuration
public class ServiceLocatorConfig {

    @Bean
    @RequestScope
    public SomeService serviceByKey(WebRequest request, Map<String, SomeService> services) {

        // This is where I need a hand -- how would I get the request body?
        String serviceId = readServiceIdFromRequestBody(request);
        return services[key];
    }

}

So far I'm receiving the request in my @Bean, but haven't had any success getting the request body. The closest I've gotten is by blindly experimenting with ContentCachingRequestWrapper, but I've always received null when calling .getContentAsByteArray(). It also sounds as though it requires a form-encoded body -- so the custom content type (which can't be modified in this case) may be causing more trouble.

How can a Spring Bean inspect a HTTP request?

In order to achieve what you need you can make use of a WebFilter which will work as an interceptor for incoming requests before it reaches your services, it will have access the json payload and you can read the incoming parameter and call the appropriate component to handle the request.

Your WebFilter class will look similar to this one (on this example we are intercepting requests to '/rest/*':

import java.io.IOException;
import java.nio.charset.Charset;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import org.apache.commons.io.IOUtils;
import org.springframework.web.context.support.WebApplicationContextUtils;
@WebFilter(urlPatterns = "/rest/*")
public class DoSomethingInterceptor implements Filter {
private FilterConfig filterConfig;
@Override
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig = filterConfig;
}
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
HttpServletRequest httpRequest = (HttpServletRequest) request;
//Parse the json from request
String jsonPayload = IOUtils.toString(request.getInputStream(), Charset.defaultCharset());
IncomingRequest jsonRequest = mapper.readValue(jsonPayload, IncomingRequest.class);
//Read the service parameter
String serviceClass = jsonRequest.getServiceClass();
//Map the incoming service to your service class
Class<MyService> myServiceClass = ServiceType.get(serviceClass);
//Get the bean from Spring context
DoSomething bean =
(DoSomething) WebApplicationContextUtils.
getRequiredWebApplicationContext(filterConfig.getServletContext()).
getBean(myServiceClass);
//Call the method in the service
String resultFromService = bean.doSomething();
//Finally you will copy the result from service to the http response
response.getOutputStream().write(resultFromService);
return;
}
}

Also remember to register your WebFilter on Spring, for SpringBoot app it can be done like in below example:

@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
@Bean
@Autowired
public FilterRegistrationBean registerFilter() {
FilterRegistrationBean filterRegistration = new FilterRegistrationBean();
filterRegistration.setFilter(new DoSomethingInterceptor());
List<String> urlPatterns = new ArrayList<>();
urlPatterns.add("/rest/*");
filterRegistration.setUrlPatterns(urlPatterns);
return filterRegistration;
}