Add Java NIO code snippets

11-network-ii/snippets/echoclientserver/src/bg/sofia/uni/fmi/mjt/echo/nio/EchoClient.java

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+package bg.sofia.uni.fmi.mjt.echo.nio;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.PrintWriter;
+import java.net.InetSocketAddress;
+import java.nio.channels.Channels;
+import java.nio.channels.SocketChannel;
+import java.util.Scanner;
+
+// NIO specifics wrapped & hidden
+public class EchoClient {
+
+    private static final int SERVER_PORT = 7777;
+
+    public static void main(String[] args) {
+
+        try (SocketChannel socketChannel = SocketChannel.open();
+             BufferedReader reader = new BufferedReader(Channels.newReader(socketChannel, "UTF-8"));
+             PrintWriter writer = new PrintWriter(Channels.newWriter(socketChannel, "UTF-8"), true);
+             Scanner scanner = new Scanner(System.in)) {
+
+            socketChannel.connect(new InetSocketAddress("localhost", SERVER_PORT));
+
+            System.out.println("Connected to the server.");
+
+            while (true) {
+                System.out.print("Enter message: ");
+                String message = scanner.nextLine(); // read a line from the console
+
+                if ("quit".equals(message)) {
+                    break;
+                }
+
+                System.out.println("Sending message <" + message + "> to the server...");
+
+                writer.println(message);
+
+                String reply = reader.readLine(); // read the response from the server
+                System.out.println("The server replied <" + reply + ">");
+            }
+        } catch (IOException e) {
+            throw new RuntimeException("There is a problem with the network communication", e);
+        }
+    }
+}

11-network-ii/snippets/echoclientserver/src/bg/sofia/uni/fmi/mjt/echo/nio/EchoClientNio.java

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+package bg.sofia.uni.fmi.mjt.echo.nio;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.nio.channels.SocketChannel;
+import java.util.Scanner;
+
+// NIO, blocking
+public class EchoClientNio {
+
+    private static final int SERVER_PORT = 7777;
+    private static final String SERVER_HOST = "localhost";
+    private static final int BUFFER_SIZE = 512;
+
+    private static ByteBuffer buffer = ByteBuffer.allocateDirect(BUFFER_SIZE);
+
+    public static void main(String[] args) {
+
+        try (SocketChannel socketChannel = SocketChannel.open();
+             Scanner scanner = new Scanner(System.in)) {
+
+            socketChannel.connect(new InetSocketAddress(SERVER_HOST, SERVER_PORT));
+
+            System.out.println("Connected to the server.");
+
+            while (true) {
+                System.out.print("Enter message: ");
+                String message = scanner.nextLine(); // read a line from the console
+
+                if ("quit".equals(message)) {
+                    break;
+                }
+
+                System.out.println("Sending message <" + message + "> to the server...");
+
+                buffer.clear(); // switch to writing mode
+                buffer.put(message.getBytes()); // buffer fill
+                buffer.flip(); // switch to reading mode
+                socketChannel.write(buffer); // buffer drain
+
+                buffer.clear(); // switch to writing mode
+                socketChannel.read(buffer); // buffer fill
+                buffer.flip(); // switch to reading mode
+
+                byte[] byteArray = new byte[buffer.remaining()];
+                buffer.get(byteArray);
+                String reply = new String(byteArray, "UTF-8"); // buffer drain
+
+                // if buffer is a non-direct one, is has a wrapped array and we can get it
+                //String reply = new String(buffer.array(), 0, buffer.position(), "UTF-8"); // buffer drain
+
+                System.out.println("The server replied <" + reply + ">");
+            }
+
+        } catch (IOException e) {
+            throw new RuntimeException("There is a problem with the network communication", e);
+        }
+    }
+}

11-network-ii/snippets/echoclientserver/src/bg/sofia/uni/fmi/mjt/echo/nio/EchoServer.java

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+package bg.sofia.uni.fmi.mjt.echo.nio;
+
+import java.io.IOException;
+import java.net.InetSocketAddress;
+import java.nio.ByteBuffer;
+import java.nio.channels.SelectionKey;
+import java.nio.channels.Selector;
+import java.nio.channels.ServerSocketChannel;
+import java.nio.channels.SocketChannel;
+import java.util.Iterator;
+import java.util.Set;
+
+public class EchoServer {
+    public static final int SERVER_PORT = 7777;
+    private static final String SERVER_HOST = "localhost";
+    private static final int BUFFER_SIZE = 1024;
+
+    public static void main(String[] args) {
+        try (ServerSocketChannel serverSocketChannel = ServerSocketChannel.open()) {
+
+            serverSocketChannel.bind(new InetSocketAddress(SERVER_HOST, SERVER_PORT));
+            serverSocketChannel.configureBlocking(false);
+
+            Selector selector = Selector.open();
+            serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT);
+
+            ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);
+
+            while (true) {
+                int readyChannels = selector.select();
+                if (readyChannels == 0) {
+                    // select() is blocking but may still return with 0, check javadoc
+                    continue;
+                }
+
+                Set<SelectionKey> selectedKeys = selector.selectedKeys();
+                Iterator<SelectionKey> keyIterator = selectedKeys.iterator();
+
+                while (keyIterator.hasNext()) {
+                    SelectionKey key = keyIterator.next();
+                    if (key.isReadable()) {
+                        SocketChannel sc = (SocketChannel) key.channel();
+
+                        buffer.clear();
+                        int r = sc.read(buffer);
+                        if (r < 0) {
+                            System.out.println("Client has closed the connection");
+                            sc.close();
+                            continue;
+                        }
+                        buffer.flip();
+                        sc.write(buffer);
+
+                    } else if (key.isAcceptable()) {
+                        ServerSocketChannel sockChannel = (ServerSocketChannel) key.channel();
+                        SocketChannel accept = sockChannel.accept();
+                        accept.configureBlocking(false);
+                        accept.register(selector, SelectionKey.OP_READ);
+                    }
+
+                    keyIterator.remove();
+                }
+
+            }
+
+        } catch (IOException e) {
+            throw new RuntimeException("There is a problem with the server socket", e);
+        }
+    }
+}