Important: This news article covers an old version of Javalin (v4.0.1). The current version is v6.1.3.
See the documentation page for up-to-date information.


  • A bug was introduced in Javalin 4, which made Javalin fail to terminate SSE messages properly. This has been fixed.
  • A possible race condition in async handling has been fixed
  • The ValidationException class is now a RuntimeException rather than an Exception
  • There was a memory leak in GZIP handling which has been plugged