RSocketFactory wrapping constructors (#788)

Allow RSocketFactory to be created with a pre-created instance of
RSocketConnector or RSocketServer. This helps higher level frameworks
to support both old and current APIs.

Signed-off-by: Rossen Stoyanchev <rstoyanchev@pivotal.io>

Author: rstoyanchev

rsocket-core/src/main/java/io/rsocket/RSocketFactory.java

@@ -97,14 +97,22 @@ default <T extends Closeable> Start<T> transport(ServerTransport<T> transport) {
 
   /** Factory to create and configure an RSocket client, and connect to a server. */
   public static class ClientRSocketFactory implements ClientTransportAcceptor {
-    private final RSocketConnector connector = RSocketConnector.create();
+    private final RSocketConnector connector;
 
     private Duration tickPeriod = Duration.ofSeconds(20);
     private Duration ackTimeout = Duration.ofSeconds(30);
     private int missedAcks = 3;
 
     private Resume resume;
 
+    public ClientRSocketFactory() {
+      this(RSocketConnector.create());
+    }
+
+    public ClientRSocketFactory(RSocketConnector connector) {
+      this.connector = connector;
+    }
+
     public ClientRSocketFactory byteBufAllocator(ByteBufAllocator allocator) {
       connector.byteBufAllocator(allocator);
       return this;
@@ -375,10 +383,18 @@ public ClientRSocketFactory frameDecoder(PayloadDecoder payloadDecoder) {
 
   /** Factory to create, configure, and start an RSocket server. */
   public static class ServerRSocketFactory implements ServerTransportAcceptor {
-    private final RSocketServer server = RSocketServer.create();
+    private final RSocketServer server;
 
     private Resume resume;
 
+    public ServerRSocketFactory() {
+      this(RSocketServer.create());
+    }
+
+    public ServerRSocketFactory(RSocketServer server) {
+      this.server = server;
+    }
+
     public ServerRSocketFactory byteBufAllocator(ByteBufAllocator allocator) {
       server.byteBufAllocator(allocator);
       return this;