NPE on already bound port

src/main/java/org/java_websocket/server/WebSocketServer.java

@@ -253,7 +253,7 @@ public void stop( int timeout ) throws InterruptedException {
 		wsf.close();
 
 		synchronized ( this ) {
-			if( selectorthread != null  ) {
+			if( selectorthread != null  && selector != null) {
 				selector.wakeup();
 				selectorthread.join( timeout );
 			}
@@ -319,12 +319,6 @@ public void run() {
 			onStart();
 		} catch ( IOException ex ) {
 			handleFatal( null, ex );
-			//Shutting down WebSocketWorkers, see #222
-			if( decoders != null ) {
-				for( WebSocketWorker w : decoders ) {
-					w.interrupt();
-				}
-			}
 			return;
 		}
 		try {
@@ -535,6 +529,15 @@ private void handleIOException( SelectionKey key, WebSocket conn, IOException ex
 
 	private void handleFatal( WebSocket conn, Exception e ) {
 		onError( conn, e );
+		//Shutting down WebSocketWorkers, see #222
+		if( decoders != null ) {
+			for( WebSocketWorker w : decoders ) {
+				w.interrupt();
+			}
+		}
+		if (selectorthread != null) {
+			selectorthread.interrupt();
+		}
 		try {
 			stop();
 		} catch ( IOException e1 ) {

src/test/java/org/java_websocket/issues/Issue661Test.java

@@ -0,0 +1,137 @@
+/*
+ * Copyright (c) 2010-2018 Nathan Rajlich
+ *
+ *  Permission is hereby granted, free of charge, to any person
+ *  obtaining a copy of this software and associated documentation
+ *  files (the "Software"), to deal in the Software without
+ *  restriction, including without limitation the rights to use,
+ *  copy, modify, merge, publish, distribute, sublicense, and/or sell
+ *  copies of the Software, and to permit persons to whom the
+ *  Software is furnished to do so, subject to the following
+ *  conditions:
+ *
+ *  The above copyright notice and this permission notice shall be
+ *  included in all copies or substantial portions of the Software.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ *  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+ *  OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ *  NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+ *  HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+ *  WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ *  FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ *  OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+package org.java_websocket.issues;
+
+import org.java_websocket.WebSocket;
+import org.java_websocket.handshake.ClientHandshake;
+import org.java_websocket.server.WebSocketServer;
+import org.java_websocket.util.SocketUtil;
+import org.java_websocket.util.ThreadCheck;
+import org.junit.Rule;
+import org.junit.Test;
+
+import java.io.OutputStream;
+import java.io.PrintStream;
+import java.net.BindException;
+import java.net.InetSocketAddress;
+import java.util.concurrent.CountDownLatch;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
+
+public class Issue661Test {
+
+	@Rule
+	public ThreadCheck zombies = new ThreadCheck();
+
+	private CountDownLatch countServerDownLatch = new CountDownLatch( 1 );
+
+	private boolean wasError = false;
+
+	class TestPrintStream extends PrintStream {
+		public TestPrintStream( OutputStream out ) {
+			super( out );
+		}
+
+		@Override
+		public void println( Object o ) {
+			wasError = true;
+			super.println( o );
+		}
+	}
+
+	@Test(timeout =  2000)
+	public void testIssue() throws Exception {
+		System.setErr( new TestPrintStream( System.err ) );
+		int port = SocketUtil.getAvailablePort();
+		WebSocketServer server0 = new WebSocketServer( new InetSocketAddress( port ) ) {
+			@Override
+			public void onOpen( WebSocket conn, ClientHandshake handshake ) {
+				fail( "There should be no onOpen" );
+			}
+
+			@Override
+			public void onClose( WebSocket conn, int code, String reason, boolean remote ) {
+				fail( "There should be no onClose" );
+			}
+
+			@Override
+			public void onMessage( WebSocket conn, String message ) {
+				fail( "There should be no onMessage" );
+			}
+
+			@Override
+			public void onError( WebSocket conn, Exception ex ) {
+				fail( "There should be no onError!" );
+			}
+
+			@Override
+			public void onStart() {
+				countServerDownLatch.countDown();
+			}
+		};
+		server0.start();
+		try {
+			countServerDownLatch.await();
+		} catch ( InterruptedException e ) {
+			//
+		}
+		WebSocketServer server1 = new WebSocketServer( new InetSocketAddress( port ) ) {
+			@Override
+			public void onOpen( WebSocket conn, ClientHandshake handshake ) {
+				fail( "There should be no onOpen" );
+			}
+
+			@Override
+			public void onClose( WebSocket conn, int code, String reason, boolean remote ) {
+				fail( "There should be no onClose" );
+			}
+
+			@Override
+			public void onMessage( WebSocket conn, String message ) {
+				fail( "There should be no onMessage" );
+			}
+
+			@Override
+			public void onError( WebSocket conn, Exception ex ) {
+				if( !( ex instanceof BindException ) ) {
+					fail( "There should be no onError" );
+				}
+			}
+
+			@Override
+			public void onStart() {
+				fail( "There should be no onStart!" );
+			}
+		};
+		server1.start();
+		Thread.sleep( 1000 );
+		server1.stop();
+		server0.stop();
+		Thread.sleep( 100 );
+		assertTrue( "There was an error using System.err", !wasError );
+	}
+}