Eliminate need for rxJava in Json Encoder

spring-web-reactive/src/main/java/org/springframework/reactive/codec/encoder/JsonObjectEncoder.java

@@ -16,48 +16,94 @@
 
 package org.springframework.reactive.codec.encoder;
 
-import java.nio.ByteBuffer;
-
 import org.reactivestreams.Publisher;
-import reactor.rx.Promise;
-import rx.Observable;
-import rx.RxReactiveStreams;
-
+import org.reactivestreams.Subscriber;
 import org.springframework.core.ResolvableType;
 import org.springframework.http.MediaType;
 import org.springframework.reactive.codec.decoder.JsonObjectDecoder;
+import org.springframework.util.ClassUtils;
+
+import reactor.core.subscriber.SubscriberBarrier;
+import reactor.io.buffer.Buffer;
+import reactor.rx.Promise;
+import rx.Observable;
+
+import java.nio.ByteBuffer;
+import java.util.Arrays;
+
+import static reactor.Publishers.*;
 
 /**
  * Encode a bye stream of individual JSON element to a byte stream representing a single
  * JSON array when {@code Hints.ENCODE_AS_ARRAY} is enabled.
  *
  * @author Sebastien Deleuze
+ * @author Stephane Maldini
+ *
  * @see JsonObjectDecoder
  */
 public class JsonObjectEncoder implements MessageToByteEncoder<ByteBuffer> {
 
-	private final ByteBuffer START_ARRAY = ByteBuffer.wrap("[".getBytes());
+	private static final boolean rxJava1Present =
+			ClassUtils.isPresent("rx.Observable", JsonObjectEncoder.class.getClassLoader());
+
+	private static final boolean reactorPresent =
+			ClassUtils.isPresent("reactor.rx.Promise", JsonObjectEncoder.class.getClassLoader());
 
-	private final ByteBuffer END_ARRAY = ByteBuffer.wrap("]".getBytes());
+	final ByteBuffer START_ARRAY = ByteBuffer.wrap("[".getBytes());
 
-	private final ByteBuffer COMMA = ByteBuffer.wrap(",".getBytes());
+	final ByteBuffer END_ARRAY = ByteBuffer.wrap("]".getBytes());
+
+	final ByteBuffer COMMA = ByteBuffer.wrap(",".getBytes());
 
 
 	@Override
 	public boolean canEncode(ResolvableType type, MediaType mediaType, Object... hints) {
-		return mediaType.isCompatibleWith(MediaType.APPLICATION_JSON) && !Promise.class.isAssignableFrom(type.getRawClass()) &&
-				(Observable.class.isAssignableFrom(type.getRawClass()) || Publisher.class.isAssignableFrom(type.getRawClass()));
+		return mediaType.isCompatibleWith(MediaType.APPLICATION_JSON) &&
+				!(reactorPresent && Promise.class.isAssignableFrom(type.getRawClass())) &&
+				(rxJava1Present && Observable.class.isAssignableFrom(type.getRawClass())
+				|| Publisher.class.isAssignableFrom(type.getRawClass()));
 	}
 
 	@Override
-	public Publisher<ByteBuffer> encode(Publisher<? extends ByteBuffer> messageStream, ResolvableType type, MediaType mediaType, Object... hints) {
-		// TODO We use RxJava Observable because there is no skipLast() operator in Reactor
-		// TODO Merge some chunks, there is no need to have chunks with only '[', ']' or ',' characters
-		return RxReactiveStreams.toPublisher(
-				Observable.concat(
-						Observable.just(START_ARRAY),
-						RxReactiveStreams.toObservable(messageStream).flatMap(b -> Observable.just(b, COMMA)).skipLast(1),
-						Observable.just(END_ARRAY)));
+	public Publisher<ByteBuffer> encode(Publisher<? extends ByteBuffer> messageStream, ResolvableType type, MediaType
+	  mediaType, Object... hints) {
+		//TODO Merge some chunks, there is no need to have chunks with only '[', ']' or ',' characters
+		return
+		  concat(
+			  from(
+			    Arrays.<Publisher<ByteBuffer>>asList(
+				  just(START_ARRAY),
+				  lift(
+				    flatMap(messageStream, (ByteBuffer b) -> from(Arrays.asList(b, COMMA))),
+				    sub -> new SkipLastBarrier(sub)
+				  ),
+				  just(END_ARRAY)
+			    )
+			  )
+		  );
 	}
 
+	private static class SkipLastBarrier extends SubscriberBarrier<ByteBuffer, ByteBuffer> {
+
+		public SkipLastBarrier(Subscriber<? super ByteBuffer> subscriber) {
+			super(subscriber);
+		}
+
+		ByteBuffer prev = null;
+
+		@Override
+		protected void doNext(ByteBuffer next) {
+			if (prev == null) {
+				prev = next;
+				doRequest(1);
+				return;
+			}
+
+			ByteBuffer tmp = prev;
+			prev = next;
+			subscriber.onNext(tmp);
+		}
+
+	}
 }