Question

I write to socket with:

OutputStream socketStream = socket.getOutputStream();
socketStream.write(buf);

But this can throw IOException, so I do:

try {
  OutputStream socketStream = socket.getOutputStream();
  socketStream.write(buf);
} catch (IOException e) {
  // logging
} finally {
  socket.close();
}

1. But socket.close also force me to catch IOException! So do I need try ... catch it again in finally?

2. When catch IOException from close, it mean socket not closed? So try close again? Or what to do?

Thanks

Answer 1

close() throws IOException because closing something usually implies calling flush(), and flushing might fail. For example, if you lose network connectivity and issue socket.close(), you cannot flush whatever you have buffered, so flush() will throw an exception. Because data might be lost, the exception is checked, so you are forced to deal with that possibility.

I think the best way to deal with this is:

try {
    OutputStream socketStream = socket.getOutputStream();
    socketStream.write(buf);
    socket.close();
} catch (IOException e) {
    // try to deal with your I/O error; do logging
} finally {
    closeSilently(socket);
}
...
// Somewhere else, usually part of an utility JAR like Apache Commons IO
public static void closeSilently(Socket s) {
    if (socket != null) {
        try {
            socket.close();
        } catch (IOException e2) {
            // do more logging if appropiate
        }
    }
}

This code will work normally in the common case. If something goes wrong (even inside close()), it will allow you to catch the exception and do something before unconditionally closing your socket and swallowing everything it might throw.