Add Java network programming code snippets

11-network-ii/snippets/echoclientserver/src/bg/sofia/uni/fmi/mjt/echo/net/multithreaded/ClientRequestHandler.java

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+package bg.sofia.uni.fmi.mjt.echo.net.multithreaded;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.Socket;
+
+public class ClientRequestHandler implements Runnable {
+
+    private Socket socket;
+
+    public ClientRequestHandler(Socket socket) {
+        this.socket = socket;
+    }
+
+    @Override
+    public void run() {
+
+        Thread.currentThread().setName("Client Request Handler for " + socket.getRemoteSocketAddress());
+
+        try (PrintWriter out = new PrintWriter(socket.getOutputStream(), true); // autoflush on
+             BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()))) {
+
+            String inputLine;
+            while ((inputLine = in.readLine()) != null) { // read the message from the client
+                System.out.println("Message received from client: " + inputLine);
+                out.println("Echo " + inputLine); // send response back to the client
+            }
+
+        } catch (IOException e) {
+            System.out.println(e.getMessage());
+        } finally {
+            try {
+                socket.close();
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        }
+
+    }
+
+}

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

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+package bg.sofia.uni.fmi.mjt.echo.net.multithreaded;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.Socket;
+import java.util.Scanner;
+
+public class EchoClient {
+
+    private static final int SERVER_PORT = 4444;
+
+    public static void main(String[] args) {
+
+        try (Socket socket = new Socket("localhost", SERVER_PORT);
+             PrintWriter writer = new PrintWriter(socket.getOutputStream(), true); // autoflush on
+             BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
+             Scanner scanner = new Scanner(System.in)) {
+
+            Thread.currentThread().setName("Echo client thread " + socket.getLocalPort());
+
+            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); // send the message to the server
+
+                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/net/multithreaded/EchoServer.java

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+package bg.sofia.uni.fmi.mjt.echo.net.multithreaded;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public class EchoServer {
+
+    private static final int SERVER_PORT = 4444;
+    private static final int MAX_EXECUTOR_THREADS = 10;
+
+    public static void main(String[] args) {
+
+        ExecutorService executor = Executors.newFixedThreadPool(MAX_EXECUTOR_THREADS);
+
+        Thread.currentThread().setName("Echo Server Thread");
+
+        try (ServerSocket serverSocket = new ServerSocket(SERVER_PORT)) {
+
+            System.out.println("Server started and listening for connect requests");
+
+            Socket clientSocket;
+
+            while (true) {
+
+                // Calling accept() blocks and waits for connection request by a client
+                // When a request comes, accept() returns a socket to communicate with this
+                // client
+                clientSocket = serverSocket.accept();
+
+                System.out.println("Accepted connection request from client " + clientSocket.getInetAddress());
+
+                // We want each client to be processed in a separate thread
+                // to keep the current thread free to accept() requests from new clients
+                ClientRequestHandler clientHandler = new ClientRequestHandler(clientSocket);
+
+                // uncomment the line below to launch a thread manually
+                // new Thread(clientHandler).start();
+                executor.execute(clientHandler); // use a thread pool to launch a thread
+            }
+
+        } catch (IOException e) {
+            throw new RuntimeException("There is a problem with the server socket", e);
+        }
+    }
+
+}

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

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+package bg.sofia.uni.fmi.mjt.echo.net.simple;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.Socket;
+import java.util.Scanner;
+
+public class EchoClient {
+
+    private static final int SERVER_PORT = 6666;
+
+    public static void main(String[] args) {
+
+        try (Socket socket = new Socket("localhost", SERVER_PORT);
+             PrintWriter writer = new PrintWriter(socket.getOutputStream(), true); // autoflush on
+             BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
+             Scanner scanner = new Scanner(System.in)) {
+
+            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); // send the message to the server
+
+                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/net/simple/EchoServer.java

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+package bg.sofia.uni.fmi.mjt.echo.net.simple;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.ServerSocket;
+import java.net.Socket;
+
+public class EchoServer {
+
+    private static final int SERVER_PORT = 6666;
+
+    public static void main(String[] args) {
+
+        try (ServerSocket serverSocket = new ServerSocket(SERVER_PORT)) {
+            System.out.println("Server started and listening for connect request");
+
+            try (Socket clientSocket = serverSocket.accept();
+                 BufferedReader br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+                 PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true)) { // autoflush on
+
+                String inputLine;
+                while ((inputLine = br.readLine()) != null) {
+                    System.out.println("Message received from client: " + inputLine);
+                    out.println("Echo " + inputLine);
+                }
+            }
+
+        } catch (IOException e) {
+            throw new RuntimeException("There is a problem with the server socket", e);
+        }
+    }
+
+}

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 the buffer is a non-direct one, it 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);
+        }
+    }
+}