Update RedisOperations#convertAndSend to return number of clients receiving the message.

Currently, `RedisOperations#convertAndSend` is void event though the underlying `RedisPubSubCommands#publish` returns a `Long` that represents the number of clients receiving the published message (see https://redis.io/commands/publish).

This commit updates `RedisOperations#convertAndSend` to return the number of clients that received the message.

Closes #2209
Original pull request: #2225.

src/main/java/org/springframework/data/redis/core/RedisOperations.java

@@ -46,6 +46,7 @@ import org.springframework.util.Assert;
  * @author ihaohong
  * @author Todd Merrill
  * @author Chen Li
+ * @author Vedran Pavic
  */
 public interface RedisOperations<K, V> {
 
@@ -591,9 +592,11 @@ public interface RedisOperations<K, V> {
 	 *
 	 * @param destination the channel to publish to, must not be {@literal null}.
 	 * @param message message to publish
+	 * @return the number of clients that received the message
 	 * @see <a href="https://redis.io/commands/publish">Redis Documentation: PUBLISH</a>
 	 */
-	void convertAndSend(String destination, Object message);
+	@Nullable
+	Long convertAndSend(String destination, Object message);
 
 	// -------------------------------------------------------------------------
 	// Methods to obtain specific operations interface objects.

src/main/java/org/springframework/data/redis/core/RedisTemplate.java

@@ -86,6 +86,7 @@ import org.springframework.util.CollectionUtils;
  * @author Denis Zavedeev
  * @author ihaohong
  * @author Chen Li
+ * @author Vedran Pavic
  * @param <K> the Redis key type against which the template works (usually a String)
  * @param <V> the Redis value type against which the template works
  * @see StringRedisTemplate
@@ -942,14 +943,14 @@ public class RedisTemplate<K, V> extends RedisAccessor implements RedisOperation
 	}
 
 	@Override
-	public void convertAndSend(String channel, Object message) {
+	public Long convertAndSend(String channel, Object message) {
 
 		Assert.hasText(channel, "a non-empty channel is required");
 
 		byte[] rawChannel = rawString(channel);
 		byte[] rawMessage = rawValue(message);
 
-		executeWithoutResult(connection -> connection.publish(rawChannel, rawMessage));
+		return execute(connection -> connection.publish(rawChannel, rawMessage), true);
 	}
 
 	private void executeWithoutResult(Consumer<RedisConnection> action) {