Sockets: Discover port availability using Java

This is the implementation coming from the Apache camel project:

/** * Checks to see if a specific port is available. * * @param port the port to check for availability */public static boolean available(int port) {    if (port < MIN_PORT_NUMBER || port > MAX_PORT_NUMBER) {        throw new IllegalArgumentException("Invalid start port: " + port);    }    ServerSocket ss = null;    DatagramSocket ds = null;    try {        ss = new ServerSocket(port);        ss.setReuseAddress(true);        ds = new DatagramSocket(port);        ds.setReuseAddress(true);        return true;    } catch (IOException e) {    } finally {        if (ds != null) {            ds.close();        }        if (ss != null) {            try {                ss.close();            } catch (IOException e) {                /* should not be thrown */            }        }    }    return false;}

They are checking the DatagramSocket as well to check if the port is avaliable in UDP and TCP.

Hope this helps.

For Java 7 you can use try-with-resource for more compact code:

private static boolean available(int port) {    try (Socket ignored = new Socket("localhost", port)) {        return false;    } catch (IOException ignored) {        return true;    }}

It appears that as of Java 7, David Santamaria's answer doesn't work reliably any more. It looks like you can still reliably use a Socket to test the connection, however.

private static boolean available(int port) {    System.out.println("--------------Testing port " + port);    Socket s = null;    try {        s = new Socket("localhost", port);        // If the code makes it this far without an exception it means        // something is using the port and has responded.        System.out.println("--------------Port " + port + " is not available");        return false;    } catch (IOException e) {        System.out.println("--------------Port " + port + " is available");        return true;    } finally {        if( s != null){            try {                s.close();            } catch (IOException e) {                throw new RuntimeException("You should handle this error." , e);            }        }    }}