Fix failing test in CancelWithoutDemandCodecTests

The test started failing after recent commit
e370c15bc6.

See gh-29038

spring-web/src/main/java/org/springframework/http/codec/json/AbstractJackson2Encoder.java

@@ -36,7 +36,6 @@ import com.fasterxml.jackson.databind.ObjectWriter;
 import com.fasterxml.jackson.databind.SequenceWriter;
 import com.fasterxml.jackson.databind.exc.InvalidDefinitionException;
 import com.fasterxml.jackson.databind.ser.FilterProvider;
-import org.apache.commons.logging.Log;
 import org.reactivestreams.Publisher;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
@@ -182,20 +181,23 @@ public abstract class AbstractJackson2Encoder extends Jackson2CodecSupport imple
 				// Do not prepend JSON array prefix until first signal is known, onNext vs onError
 				// Keeps response not committed for error handling
 
-				Flux<DataBuffer> flux1 = helper.getPrefix(bufferFactory, hints, logger)
-						.concatWith(Flux.just(EMPTY_BUFFER).repeat());
+				dataBufferFlux = Flux.from(inputStream)
+						.map(value -> {
+							byte[] prefix = helper.getPrefix();
+							byte[] delimiter = helper.getDelimiter();
 
-				Flux<DataBuffer> flux2 = Flux.from(inputStream).map(value -> encodeStreamingValue(
-						value, bufferFactory, hints, sequenceWriter, byteBuilder, helper.getDelimiter(), EMPTY_BYTES));
+							DataBuffer dataBuffer = encodeStreamingValue(
+									value, bufferFactory, hints, sequenceWriter, byteBuilder, delimiter, EMPTY_BYTES);
 
-				dataBufferFlux = Flux.zip(flux1, flux2, (buffer1, buffer2) ->
-								(buffer1 != EMPTY_BUFFER ?
-										bufferFactory.join(Arrays.asList(buffer1, buffer2)) :
-										buffer2))
-						.concatWith(helper.getSuffix(bufferFactory, hints, logger));
+							return (prefix.length > 0 ?
+									bufferFactory.join(Arrays.asList(bufferFactory.wrap(prefix), dataBuffer)) :
+									dataBuffer);
+						})
+						.concatWith(Mono.fromCallable(() -> bufferFactory.wrap(helper.getSuffix())));
 			}
 
 			return dataBufferFlux
+					.doOnNext(dataBuffer ->	Hints.touchDataBuffer(dataBuffer, hints, logger))
 					.doAfterTerminate(() -> {
 						try {
 							byteBuilder.release();
@@ -420,33 +422,22 @@ public abstract class AbstractJackson2Encoder extends Jackson2CodecSupport imple
 
 		private static final byte[] CLOSE_BRACKET = {']'};
 
-
-		private boolean afterFirstItem = false;
+		private boolean firstItemEmitted;
 
 		public byte[] getDelimiter() {
-			if (this.afterFirstItem) {
+			if (this.firstItemEmitted) {
 				return COMMA_SEPARATOR;
 			}
-			this.afterFirstItem = true;
+			this.firstItemEmitted = true;
 			return EMPTY_BYTES;
 		}
 
-		public Mono<DataBuffer> getPrefix(DataBufferFactory factory, @Nullable Map<String, Object> hints, Log logger) {
-			return wrapBytes(OPEN_BRACKET, factory, hints, logger);
-		}
-
-		public Mono<DataBuffer> getSuffix(DataBufferFactory factory, @Nullable Map<String, Object> hints, Log logger) {
-			return wrapBytes(CLOSE_BRACKET, factory, hints, logger);
+		public byte[] getPrefix() {
+			return (this.firstItemEmitted ? EMPTY_BYTES : OPEN_BRACKET);
 		}
 
-		private Mono<DataBuffer> wrapBytes(
-				byte[] bytes, DataBufferFactory bufferFactory, @Nullable Map<String, Object> hints, Log logger) {
-
-			return Mono.fromCallable(() -> {
-				DataBuffer buffer = bufferFactory.wrap(bytes);
-				Hints.touchDataBuffer(buffer, hints, logger);
-				return buffer;
-			});
+		public byte[] getSuffix() {
+			return CLOSE_BRACKET;
 		}
 	}