Document how HandlerInterceptor should differentiate an ASYNC dispatch [SPR-12608]

[spring-projects-issues]

Francisco Lozano opened SPR-12608 and commented

HandlerIntercetor#preHandle is invoked twice in an async scenario.

The problem is that it's not documented how to differentiate and avoid double-executing some logic. As it's a very common problem when using interceptors and using async handling, adding some explicit doc about how to handle would help.

if (DispatcherType.ASYNC.equals(request.getDispatcherType())) {
          return true;                
}
doStuffAsUsual();
return whatever;

---

Affects: 4.1.4

Reference URL: https://github.com/flozano/spring-interceptor-async-test

Issue Links:

• HTTP Streaming and Server-Sent Events (SSE) [SPR-12212] #16826 HTTP Streaming and Server-Sent Events (SSE)
• Document how HandlerInterceptor can hook into async request timedout [SPR-12720] #17317 Document how HandlerInterceptor can hook into async request timedout

Referenced from: commits 1803978

[spring-projects-issues]

Rossen Stoyanchev commented

Yes that would be very helpful for explaining the whole lifecycle of an async request. We are also expanding async request handling with Server-Sent Event support and HTTP streaming (#16826) so these two can be handled together.

[spring-projects-issues]

Rossen Stoyanchev commented

I've updated the javadoc.

[spring-projects-issues]

Rossen Stoyanchev commented

Modified title (was: "Document better how to handle double-invocation of HandlerInterceptor#preHandle in async requests").