The time my Java EE technology stack disappointed me most was when I noticed some embarrassing OutOfMemoryError in the log of a server which was already in production. When I analyzed the garbage collector logs I got really scared seeing the heap usage was constantly increasing. After some days of debugging I discovered that the terrible memory leak was caused by a bug inside one of the Java EE core libraries (Jersey Client), while parsing a stupid XML response. The library was shipped with the application server, so it couldn't be replaced (unless installing a different server). I rewrote my code using the Restlet Client API and the memory leak disapperead. What a terrible week!