What is the quickest way to detect an unreachable host in Java?

Question

I would like the fastest and most accurate function boolean isReachable(String host, int port) that passes the following JUnit tests under the conditions below. Tim

Answer 1

The rate determining step for host availability is not within your own code, but in the netlag. You must wait for the host to respond, and this can take time. If your program blocks while waiting for a response it could be a problem. I got around this by creating each host as an object, each with its own threaded method for checking availability. In my own situation I have 40 hosts I keep track of. My main program loops through an array of 40 machine objects once every 20 seconds, calling the appropriate method on each to check availability. Since each machine object spawns its own thread to do this, all 40 machines are interrogated concurrently and the (up to 500ms) response time for each isn't a problem.