Baeldung/java 5187 (#11431)

* Commit source code to branch

* BAEL-5065 improvement of groupBy with complex key

* Client and Server SSLSocket implementation to support https client
authentication.

core-java-modules/core-java-11-2/src/main/java/com/baeldung/httpsclientauthentication/SSLScocketClient.java

@@ -0,0 +1,41 @@
+package com.baeldung.httpsclientauthentication;
+
+import java.io.BufferedInputStream;
+import java.io.BufferedOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+
+import javax.net.SocketFactory;
+import javax.net.ssl.SSLSocket;
+import javax.net.ssl.SSLSocketFactory;
+
+public class SSLScocketClient {
+
+    static void startClient(String host, int port) throws IOException {
+
+        SocketFactory factory = SSLSocketFactory.getDefault();
+
+        try (SSLSocket socket = (SSLSocket) factory.createSocket(host, port)) {
+            socket.setEnabledCipherSuites(new String[] { "TLS_AES_128_GCM_SHA256" });
+            socket.setEnabledProtocols(new String[] { "TLSv1.3" });
+            InputStream is = new BufferedInputStream(socket.getInputStream());
+            String message = "Hello World Message";
+            System.out.println("sending message: " + message);
+            OutputStream os = new BufferedOutputStream(socket.getOutputStream());
+            os.write(message.getBytes());
+            os.flush();
+            byte[] data = new byte[2048];
+            int len = is.read(data);
+            if (len <= 0) {
+                throw new IOException("no data received");
+            }
+            System.out.printf("client received %d bytes: %s%n", len, new String(data, 0, len));
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+
+        startClient("localhost", 8443);
+    }
+}

core-java-modules/core-java-11-2/src/main/java/com/baeldung/httpsclientauthentication/SSLSocketEchoServer.java

@@ -0,0 +1,46 @@
+package com.baeldung.httpsclientauthentication;
+
+import java.io.BufferedInputStream;
+import java.io.BufferedOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.Socket;
+
+import javax.net.ServerSocketFactory;
+import javax.net.ssl.SSLServerSocket;
+import javax.net.ssl.SSLServerSocketFactory;
+
+public class SSLSocketEchoServer {
+
+    static void startServer(int port) throws IOException {
+
+        ServerSocketFactory factory = SSLServerSocketFactory.getDefault();
+
+        try (SSLServerSocket listener = (SSLServerSocket) factory.createServerSocket(port)) {
+            listener.setNeedClientAuth(true);
+            listener.setEnabledCipherSuites(new String[] { "TLS_AES_128_GCM_SHA256" });
+            listener.setEnabledProtocols(new String[] { "TLSv1.3" });
+            System.out.println("listening for messages...");
+            try (Socket socket = listener.accept()) {
+                InputStream is = new BufferedInputStream(socket.getInputStream());
+                OutputStream os = new BufferedOutputStream(socket.getOutputStream());
+                byte[] data = new byte[2048];
+                int len = is.read(data);
+                if (len <= 0) {
+                    throw new IOException("no data received");
+                }
+                String message = new String(data, 0, len);
+                System.out.printf("server received %d bytes: %s%n", len, message);
+                String response = message + " processed by server";
+                os.write(response.getBytes(), 0, response.getBytes().length);
+                os.flush();
+            }
+            System.out.println("message processed, exiting");
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        startServer(8443);
+    }
+}