One of my student find a bug in the implementation of Scanner, that allows you to use a non blocking channel as input of a Scanner. The Scanner uses Channels.newReader() to create a Reader from a channel which itself create a StreamDecoder. In that case, StreamDecoder.impReader() goes into an infinite loop because impReader() calls readBytes() that does nothing if channel.read() returns zero. The javadoc of Channels.newReader() clearly states that it should throw a IllegalBlockingModeException but there is no code that checks that. I think a way to solve the problem is to insert a code that check the blocking state in Channels.newWriter(). if (ch instanceof SelectableChannel) { SelectableChannel sc = (SelectableChannel)ch; if (!sc.isBlocking()) throw new IllegalBlockingModeException(); } } and to document the exception in the constructor of Scanner that takes a channel. If someone provide me a bug id, it will provide a patch :) cheers, Rémi PS: The code below is a simple test to reproduce the infinite loop. ---------------------------------------------------- import java.io.IOException; import java.net.InetSocketAddress; import java.nio.ByteBuffer; import java.nio.channels.ServerSocketChannel; import java.nio.channels.SocketChannel; import java.util.Scanner; public class Main { public static void main(String[] args) throws IOException { ServerSocketChannel serverSocketChannel = ServerSocketChannel.open(); serverSocketChannel.bind(new InetSocketAddress(2332)); new Thread(new Runnable() { @Override public void run() { try { SocketChannel channel = SocketChannel.open(new InetSocketAddress("localhost", 2332)); do { channel.write(ByteBuffer.wrap(new byte[] {'A'})); Thread.sleep(1000); } while(true); } catch (IOException | InterruptedException e) { throw new AssertionError(e); } } }).start(); SocketChannel socketChannel = serverSocketChannel.accept(); socketChannel.configureBlocking(false); Scanner scanner = new Scanner(socketChannel); while(scanner.hasNextLine()) { System.out.println(scanner.nextLine()); } } }