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Thursday, February 25, 2016

Asynchronous Streaming Request Processing in Spring MVC 4.2 + Spring Boot

With the release of Spring 4.2 version, Three new classes have been introduced to handle Requests Asynchronously of the Servlet Thread. Which are;
  1. ResponseBodyEmitter
  2. SseEmitter
  3. StreamingResponseBody
ResponseBodyEmitter enables to send DeferredResult with a compatible HttpMessageConverter. Results can be emitted from threads which are not necessarily the Servlet Request Thread of the Servlet Container.

SseEmitter is used to send Server Sent Events to the Client. Server Sent Events has a fixed format and the response type for the result will be text/event-stream.

StreamingResponseBody is used to send raw unformatted data such as bytes to the client asynchronously of the Servlet Thread.

ResponseBodyEmitter and SseEmitter has a method named complete to mark its completion and StreamingResponseBody will complete when there is no more data to send. 

All three options will be keeping alive a connection to the endpoint until the end of the request.

StreamingResponseBody is particularly useful for streaming large files such as Media Files as writing of the bytes to the Response's OutputStream will be done asynchronously. StreamingResponseBody has a writeTo(OutputStream os) call back method which needs to be overridden inorder to support streaming.

I wrote a small Spring Boot Application to showcase the StreamingResponseBody capabilities in terms of Streaming large files. The application source code can be found at Below is a screen shot of the application.

In order to send the Video files streaming to the Projekktor player in the web page following code snippet is used.

And a Custom Web Configuration to over ride default timeout behavior to no timeout and finally configuring an AsyncTaskExecutor


1 comment:

Don Krapohl said...

Brilliant, thank you. Because of the response payload (many GB) from big dataset downloads in a data broker I've had to use blocking IO and writing directly to the response stream. I've not seen anyone mention this one yet and missed it scanning the spring boot docs. Much thanks.