Added NIO Selector project under core-java (#738)

* made changes to java reflection

* removed redundant method makeSound in Animal abstract class

* added project for play-framework article

* added project for regex

* changed regex project from own model to core-java

* added project for routing in play

* made changes to regex project

* refactored code for REST API with Play project

* refactored student store indexing to zero base

* added unit tests, removed bad names

* added NIO Selector project under core-java module

core-java/src/main/java/com/baeldung/java/nio/selector/EchoClient.java

@@ -0,0 +1,46 @@
+package com.baeldung.java.nio.selector;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.nio.channels.SocketChannel;
+
+public class EchoClient {
+    private static SocketChannel client = null;
+    private static ByteBuffer buffer;
+    private static EchoClient instance = null;
+
+    public static EchoClient start() {
+        if (instance == null)
+            instance = new EchoClient();
+
+        return instance;
+    }
+
+    private EchoClient() {
+        try {
+            client = SocketChannel.open(new InetSocketAddress("localhost", 5454));
+            buffer = ByteBuffer.allocate(256);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    public String sendMessage(String msg) {
+        buffer = ByteBuffer.wrap(msg.getBytes());
+        String response = null;
+        try {
+            client.write(buffer);
+            buffer.clear();
+            client.read(buffer);
+            response = new String(buffer.array()).trim();
+            System.out.println("response=" + response);
+            buffer.clear();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+        return response;
+
+    }
+
+}

core-java/src/main/java/com/baeldung/java/nio/selector/EchoServer.java

@@ -0,0 +1,50 @@
+package com.baeldung.java.nio.selector;
+
+import java.nio.channels.ServerSocketChannel;
+import java.nio.channels.SocketChannel;
+import java.nio.channels.Selector;
+import java.nio.channels.SelectionKey;
+import java.nio.ByteBuffer;
+import java.io.IOException;
+import java.util.Set;
+import java.util.Iterator;
+import java.net.InetSocketAddress;
+
+public class EchoServer {
+
+    public static void main(String[] args)
+
+    throws IOException {
+        Selector selector = Selector.open();
+        ServerSocketChannel serverSocket = ServerSocketChannel.open();
+        serverSocket.bind(new InetSocketAddress("localhost", 5454));
+        serverSocket.configureBlocking(false);
+        serverSocket.register(selector, SelectionKey.OP_ACCEPT);
+        ByteBuffer buffer = ByteBuffer.allocate(256);
+
+        while (true) {
+            selector.select();
+            Set<SelectionKey> selectedKeys = selector.selectedKeys();
+            Iterator<SelectionKey> iter = selectedKeys.iterator();
+            while (iter.hasNext()) {
+
+                SelectionKey key = iter.next();
+
+                if (key.isAcceptable()) {
+                    SocketChannel client = serverSocket.accept();
+                    client.configureBlocking(false);
+                    client.register(selector, SelectionKey.OP_READ);
+                }
+
+                if (key.isReadable()) {
+                    SocketChannel client = (SocketChannel) key.channel();
+                    client.read(buffer);
+                    buffer.flip();
+                    client.write(buffer);
+                    buffer.clear();
+                }
+                iter.remove();
+            }
+        }
+    }
+}

core-java/src/test/java/com/baeldung/java/nio/selector/EchoTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.java.nio.selector;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class EchoTest {
+
+    @Test
+    public void givenClient_whenServerEchosMessage_thenCorrect() {
+        EchoClient client = EchoClient.start();
+        String resp1 = client.sendMessage("hello");
+        String resp2 = client.sendMessage("world");
+        assertEquals("hello", resp1);
+        assertEquals("world", resp2);
+    }
+
+}