BAEL1053 - deep20jain@gmail.com - Broadcasting and Multicasting in Java (#2368)

* Adding code for java broadcasting and multicasting

* Changing multicast ip

* Adding code to iterate thorugh all network interfaces

* Formatting again and fixing bug

* Applying formatting rules on all classes

* Fixing formatting

core-java/src/main/java/com/baeldung/java/networking/udp/broadcast/BroadcastingClient.java

@@ -0,0 +1,85 @@
+package com.baeldung.java.networking.udp.broadcast;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.NetworkInterface;
+import java.net.SocketException;
+import java.util.ArrayList;
+import java.util.Enumeration;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class BroadcastingClient {
+    private DatagramSocket socket;
+    private InetAddress address;
+    private int expectedServerCount;
+    private byte[] buf;
+
+    public BroadcastingClient(int expectedServerCount) throws Exception {
+        this.expectedServerCount = expectedServerCount;
+        this.address = InetAddress.getByName("255.255.255.255");
+    }
+
+    public int discoverServers(String msg) throws IOException {
+        initializeSocketForBroadcasting();
+        copyMessageOnBuffer(msg);
+
+        // When we want to broadcast not just to local network, call listAllBroadcastAddresses() and execute broadcastPacket for each value.
+        broadcastPacket(address);
+
+        return receivePackets();
+    }
+
+    List<InetAddress> listAllBroadcastAddresses() throws SocketException {
+        List<InetAddress> broadcastList = new ArrayList<>();
+        Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
+        while (interfaces.hasMoreElements()) {
+            NetworkInterface networkInterface = interfaces.nextElement();
+
+            if (networkInterface.isLoopback() || !networkInterface.isUp()) {
+                continue;
+            }
+
+            broadcastList.addAll(networkInterface.getInterfaceAddresses()
+                .stream()
+                .filter(address -> address.getBroadcast() != null)
+                .map(address -> address.getBroadcast())
+                .collect(Collectors.toList()));
+        }
+        return broadcastList;
+    }
+
+    private void initializeSocketForBroadcasting() throws SocketException {
+        socket = new DatagramSocket();
+        socket.setBroadcast(true);
+    }
+
+    private void copyMessageOnBuffer(String msg) {
+        buf = msg.getBytes();
+    }
+
+    private void broadcastPacket(InetAddress address) throws IOException {
+        DatagramPacket packet = new DatagramPacket(buf, buf.length, address, 4445);
+        socket.send(packet);
+    }
+
+    private int receivePackets() throws IOException {
+        int serversDiscovered = 0;
+        while (serversDiscovered != expectedServerCount) {
+            receivePacket();
+            serversDiscovered++;
+        }
+        return serversDiscovered;
+    }
+
+    private void receivePacket() throws IOException {
+        DatagramPacket packet = new DatagramPacket(buf, buf.length);
+        socket.receive(packet);
+    }
+
+    public void close() {
+        socket.close();
+    }
+}

core-java/src/main/java/com/baeldung/java/networking/udp/broadcast/BroadcastingEchoServer.java

@@ -0,0 +1,44 @@
+package com.baeldung.java.networking.udp.broadcast;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+
+public class BroadcastingEchoServer extends Thread {
+
+    protected DatagramSocket socket = null;
+    protected boolean running;
+    protected byte[] buf = new byte[256];
+
+    public BroadcastingEchoServer() throws IOException {
+        socket = new DatagramSocket(null);
+        socket.setReuseAddress(true);
+        socket.bind(new InetSocketAddress(4445));
+    }
+
+    public void run() {
+        running = true;
+
+        while (running) {
+            try {
+                DatagramPacket packet = new DatagramPacket(buf, buf.length);
+                socket.receive(packet);
+                InetAddress address = packet.getAddress();
+                int port = packet.getPort();
+                packet = new DatagramPacket(buf, buf.length, address, port);
+                String received = new String(packet.getData(), 0, packet.getLength());
+                if (received.equals("end")) {
+                    running = false;
+                    continue;
+                }
+                socket.send(packet);
+            } catch (IOException e) {
+                e.printStackTrace();
+                running = false;
+            }
+        }
+        socket.close();
+    }
+}

core-java/src/main/java/com/baeldung/java/networking/udp/multicast/MulticastEchoServer.java

@@ -0,0 +1,41 @@
+package com.baeldung.java.networking.udp.multicast;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.InetAddress;
+import java.net.MulticastSocket;
+
+public class MulticastEchoServer extends Thread {
+
+    protected MulticastSocket socket = null;
+    protected byte[] buf = new byte[256];
+    protected InetAddress group = null;
+
+    public MulticastEchoServer() throws IOException {
+        socket = new MulticastSocket(4446);
+        socket.setReuseAddress(true);
+        group = InetAddress.getByName("230.0.0.0");
+        socket.joinGroup(group);
+    }
+
+    public void run() {
+        try {
+            while (true) {
+                DatagramPacket packet = new DatagramPacket(buf, buf.length);
+                socket.receive(packet);
+                InetAddress address = packet.getAddress();
+                int port = packet.getPort();
+                packet = new DatagramPacket(buf, buf.length, address, port);
+                String received = new String(packet.getData(), 0, packet.getLength());
+                if (received.equals("end")) {
+                    break;
+                }
+                socket.send(packet);
+            }
+            socket.leaveGroup(group);
+            socket.close();
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+}

core-java/src/main/java/com/baeldung/java/networking/udp/multicast/MulticastingClient.java

@@ -0,0 +1,53 @@
+package com.baeldung.java.networking.udp.multicast;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+
+public class MulticastingClient {
+    private DatagramSocket socket;
+    private InetAddress group;
+    private int expectedServerCount;
+    private byte[] buf;
+
+    public MulticastingClient(int expectedServerCount) throws Exception {
+        this.expectedServerCount = expectedServerCount;
+        this.socket = new DatagramSocket();
+        this.group = InetAddress.getByName("230.0.0.0");
+    }
+
+    public int discoverServers(String msg) throws IOException {
+        copyMessageOnBuffer(msg);
+        multicastPacket();
+
+        return receivePackets();
+    }
+
+    private void copyMessageOnBuffer(String msg) {
+        buf = msg.getBytes();
+    }
+
+    private void multicastPacket() throws IOException {
+        DatagramPacket packet = new DatagramPacket(buf, buf.length, group, 4446);
+        socket.send(packet);
+    }
+
+    private int receivePackets() throws IOException {
+        int serversDiscovered = 0;
+        while (serversDiscovered != expectedServerCount) {
+            receivePacket();
+            serversDiscovered++;
+        }
+        return serversDiscovered;
+    }
+
+    private void receivePacket() throws IOException {
+        DatagramPacket packet = new DatagramPacket(buf, buf.length);
+        socket.receive(packet);
+    }
+
+    public void close() {
+        socket.close();
+    }
+}

core-java/src/test/java/com/baeldung/java/networking/udp/broadcast/BroadcastIntegrationTest.java

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+package com.baeldung.java.networking.udp.broadcast;
+
+import org.junit.After;
+import org.junit.Test;
+
+import java.io.IOException;
+
+import static org.junit.Assert.assertEquals;
+
+public class BroadcastIntegrationTest {
+    private BroadcastingClient client;
+
+    @Test
+    public void whenBroadcasting_thenDiscoverExpectedServers() throws Exception {
+        int expectedServers = 4;
+        initializeForExpectedServers(expectedServers);
+
+        int serversDiscovered = client.discoverServers("hello server");
+        assertEquals(expectedServers, serversDiscovered);
+    }
+
+    private void initializeForExpectedServers(int expectedServers) throws Exception {
+        for (int i = 0; i < expectedServers; i++) {
+            new BroadcastingEchoServer().start();
+        }
+
+        client = new BroadcastingClient(expectedServers);
+    }
+
+    @After
+    public void tearDown() throws IOException {
+        stopEchoServer();
+        client.close();
+    }
+
+    private void stopEchoServer() throws IOException {
+        client.discoverServers("end");
+    }
+}

core-java/src/test/java/com/baeldung/java/networking/udp/multicast/MulticastIntegrationTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.java.networking.udp.multicast;
+
+import org.junit.After;
+import org.junit.Test;
+
+import java.io.IOException;
+
+import static org.junit.Assert.assertEquals;
+
+public class MulticastIntegrationTest {
+    private MulticastingClient client;
+
+    @Test
+    public void whenBroadcasting_thenDiscoverExpectedServers() throws Exception {
+        int expectedServers = 4;
+        initializeForExpectedServers(expectedServers);
+
+        int serversDiscovered = client.discoverServers("hello server");
+        assertEquals(expectedServers, serversDiscovered);
+    }
+
+    private void initializeForExpectedServers(int expectedServers) throws Exception {
+        for (int i = 0; i < expectedServers; i++) {
+            new MulticastEchoServer().start();
+        }
+
+        client = new MulticastingClient(expectedServers);
+    }
+
+    @After
+    public void tearDown() throws IOException {
+        stopEchoServer();
+        client.close();
+    }
+
+    private void stopEchoServer() throws IOException {
+        client.discoverServers("end");
+    }
+}