added client server demo

src/main/java/EchoServer.java

+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.PrintWriter;
+import java.net.ServerSocket;
+import java.net.Socket;
+
+// Adapted from https://www.baeldung.com/a-guide-to-java-sockets
+public class EchoServer {
+
+    private ServerSocket serverSocket;
+    private Socket clientSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void start(int port) throws IOException {
+        serverSocket = new ServerSocket(port);
+        clientSocket = serverSocket.accept();
+        out = new PrintWriter(clientSocket.getOutputStream(), true);
+        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+
+        String inputLine;
+        while ((inputLine = in.readLine()) != null) {
+            if (".".equals(inputLine)) {
+                out.println("good bye");
+                break;
+            }
+            out.println(inputLine.toUpperCase());
+        }
+    }
+
+    public void stop() throws IOException {
+        in.close();
+        out.close();
+        clientSocket.close();
+        serverSocket.close();
+    }
+
+    public static void main(String[] args) throws IOException {
+        EchoServer server=new EchoServer();
+        server.start(9191);
+    }
+
+}

src/main/java/GreetClient.java

+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 GreetClient {
+    private Socket clientSocket;
+    private PrintWriter out;
+    private BufferedReader in;
+
+    public void startConnection(String ip, int port) throws IOException {
+        clientSocket = new Socket(ip, port);
+        out = new PrintWriter(clientSocket.getOutputStream(), true);
+        in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
+    }
+
+    public String sendMessage(String msg) throws IOException {
+        out.println(msg);
+        String resp = in.readLine();
+        return resp;
+    }
+
+    public void stopConnection() throws IOException {
+        in.close();
+        out.close();
+        clientSocket.close();
+    }
+
+    public static void main(String[] args) throws IOException {
+        GreetClient client = new GreetClient();
+        Scanner in = new Scanner(System.in);
+        client.startConnection("127.0.0.1", 9191);
+        while (true){
+            String text = in.nextLine();
+            String response = client.sendMessage(text);
+            System.out.println("Server Response: " + response);
+
+            if (text.equals(".")){
+                break;
+            }
+        }
+
+        client.stopConnection();
+    }
+}
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