Spring Boot enable <async-supported> like in web.xml

Even though I am late to the party I am posting my working solution for posterity.

I had faced the same issue and tried the solution suggested by @Artem Bilan. But after debugging the code, I came to know that the servletRegistrationBean.isAsyncSupported() is by default true.

.

The actual error is being generated by the code block is from the method org.springframework.web.context.request.async.StandardServletAsyncWebRequest.startAsync() and we are getting this error when getRequest().isAsyncSupported() is false. Despite the ServletRegistrationBean#asyncSupported value is true, HttpServletRequest#isAsyncSupported() method value is always set to false for all API requests.

The Exerpt of the code block Code Reference

Assert.state(getRequest().isAsyncSupported(),
                "Async support must be enabled on a servlet and for all filters involved " +
                "in async request processing. This is done in Java code using the Servlet API " +
                "or by adding \"<async-supported>true</async-supported>\" to servlet and " +
                "filter declarations in web.xml.");

When analyzing further, I came to know that requestAttributes -> Globals.ASYNC_SUPPORTED_ATTR decides whether the request has to be processed in an Async way or not.

During the normal scenario, the requests do not have Globals.ASYNC_SUPPORTED_ATTR requestAttribute, hence request.asyncSupported will be false, if we manually add that requestAttribute ASYNC_SUPPORTED_ATTR value as true for all the requests using something like filters then request#asyncSupported value will be set to true as per the below code block Code Reference

specialAttributes.put(Globals.ASYNC_SUPPORTED_ATTR,
                new SpecialAttributeAdapter() {
                    @Override
                    public Object get(Request request, String name) {
                        return request.asyncSupported;
                    }

                    @Override
                    public void set(Request request, String name, Object value) {
                        Boolean oldValue = request.asyncSupported;
                        request.asyncSupported = (Boolean)value;
                        request.notifyAttributeAssigned(name, value, oldValue);
                    }
                });

Though there is no explicit answer, I have implemented a workaround for this issue. To Summarize all the required changes are listed below:

1. Add a filter to set the request attribute as request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, true)

@Component
public class AsyncSupportFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException {
        request.setAttribute(Globals.ASYNC_SUPPORTED_ATTR, true);
        chain.doFilter(request, response);
    }
}

2. Add filter to into your filter chain, in my case I have registered my filter into the spring context as below.

@Component
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
   @Autowired
   private AsyncSupportFilter asyncSupportFilter = null;
   @Override
   public void configure(HttpSecurity httpSecurity) {

       httpSecurity.addFilter(asyncSupportFilter);
       // we can add the filter before any filter like as httpSecurity.addFilterBefore(asyncSupportFilter , BasicAuthenticationFilter.class);
   }
}

Maybe it worth to mention that Spring Boot has async-support enabled by default for dispatcher servlet and all filters

Quotation from github:

We automatically set async-supported to true because the DispatcherServlet knows how to work with such requests and it's basically up to individual controller methods to return something like a DeferredResult. Furthermore, we also set async-supported for any filter (provided via getServletFilters) along with setting the DispatcherType for each filter to include ASYNC.

At least my practice supports this statement

mysolution:

@WebFilter(value = {"/subscriberinfo/query/single/*"})
public class ...Filter{
} 

TO

@WebFilter(value = {"/subscriberinfo/query/single/*"}, asyncSupported = true)
public class ...Filter{
}