Detecting Socket Disconnect Using TCP KeepAlive

You will not get far with the built-in keep-alives of the TCP stack. That's because the keep-alive interval cannot be tuned by your application, it is set by the OS, and the defaults are rather high (hours). This is not specific to Java.

If you need to time out in a reasonable time, you have to implement some kind of keep alive in the protocol to be used. Most of the high-level protocols I have seen have some kind of NOP functionality, where you send an "Are you there?" message and the other party sends a "Yes, I'm here" reply without doing anything else.

For an in-depth discussion of TCP Keep-Alives see my answer here.

But basically TCP Keep-Alives are likely the best method for detecting a stale connection. The main problem is that OS defaults are set at 2 hours before the connection is checked with 11 more minutes of Keep-Alive packets before the connection will actually be dropped.

Don't write your own application-layer Keep Alive protocol when TCP already has it built in. All you have to do is set the TCP time out to something more reasonable like 2-3 minutes.

Unfortunately, since TCP timeouts are managed at the OS level and not from within the JVM, it is difficult (but not impossible) to configure TCP timeouts from within your code on a per-socket basis.

When you call setKeepalive() on a socket the system parameters (which are tunable) are used. (Checked it under Debian 8 with openjdk7.)

Because I needed exactly the same functionality, I wrote a small library called libdontdie that can be preloaded and works with Java.