Direct exposure of StringBuilder instead of intermediate String

Closes gh-25024

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

@@ -47,10 +47,10 @@ import org.springframework.lang.Nullable;
  */
 public class ServerSentEventHttpMessageReader implements HttpMessageReader<Object> {
 
-	private static final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();
-
 	private static final ResolvableType STRING_TYPE = ResolvableType.forClass(String.class);
 
+	private static final DataBufferFactory bufferFactory = new DefaultDataBufferFactory();
+
 
 	@Nullable
 	private final Decoder<?> decoder;
@@ -58,8 +58,6 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 	private final StringDecoder lineDecoder = StringDecoder.textPlainOnly();
 
 
-
-
 	/**
 	 * Constructor without a {@code Decoder}. In this mode only {@code String}
 	 * is supported as the data of an event.
@@ -171,11 +169,11 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 			}
 		}
 
-		Object decodedData = (data != null ? decodeData(data.toString(), valueType, hints) : null);
+		Object decodedData = (data != null ? decodeData(data, valueType, hints) : null);
 
 		if (shouldWrap) {
 			if (comment != null) {
-				sseBuilder.comment(comment.toString().substring(0, comment.length() - 1));
+				sseBuilder.comment(comment.substring(0, comment.length() - 1));
 			}
 			if (decodedData != null) {
 				sseBuilder.data(decodedData);
@@ -183,19 +181,19 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 			return sseBuilder.build();
 		}
 		else {
-			return (decodedData);
+			return decodedData;
 		}
 	}
 
 	@Nullable
-	private Object decodeData(String data, ResolvableType dataType, Map<String, Object> hints) {
+	private Object decodeData(StringBuilder data, ResolvableType dataType, Map<String, Object> hints) {
 		if (String.class == dataType.resolve()) {
 			return data.substring(0, data.length() - 1);
 		}
 		if (this.decoder == null) {
 			throw new CodecException("No SSE decoder configured and the data is not String.");
 		}
-		byte[] bytes = data.getBytes(StandardCharsets.UTF_8);
+		byte[] bytes = data.toString().getBytes(StandardCharsets.UTF_8);
 		DataBuffer buffer = bufferFactory.wrap(bytes);  // wrapping only, no allocation
 		return this.decoder.decode(buffer, dataType, MediaType.TEXT_EVENT_STREAM, hints);
 	}
@@ -221,7 +219,6 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 
 		private int accumulated = 0;
 
-
 		public void afterLineParsed(String line) {
 			if (getMaxInMemorySize() < 0) {
 				return;
@@ -242,8 +239,7 @@ public class ServerSentEventHttpMessageReader implements HttpMessageReader<Objec
 
 		private void raiseLimitException() {
 			// Do not release here, it's likely down via doOnDiscard..
-			throw new DataBufferLimitException(
-					"Exceeded limit on max bytes to buffer : " + getMaxInMemorySize());
+			throw new DataBufferLimitException("Exceeded limit on max bytes to buffer : " + getMaxInMemorySize());
 		}
 	}
 

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

@@ -153,7 +153,7 @@ public class ServerSentEventHttpMessageWriter implements HttpMessageWriter<Objec
 				result = Flux.just(encodeText(sb + (String) data + "\n\n", mediaType, factory));
 			}
 			else {
-				result = encodeEvent(sb.toString(), data, dataType, mediaType, factory, hints);
+				result = encodeEvent(sb, data, dataType, mediaType, factory, hints);
 			}
 
 			return result.doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release);
@@ -161,7 +161,7 @@ public class ServerSentEventHttpMessageWriter implements HttpMessageWriter<Objec
 	}
 
 	@SuppressWarnings("unchecked")
-	private <T> Flux<DataBuffer> encodeEvent(String eventContent, T data, ResolvableType dataType,
+	private <T> Flux<DataBuffer> encodeEvent(StringBuilder eventContent, T data, ResolvableType dataType,
 			MediaType mediaType, DataBufferFactory factory, Map<String, Object> hints) {
 
 		if (this.encoder == null) {
@@ -174,16 +174,13 @@ public class ServerSentEventHttpMessageWriter implements HttpMessageWriter<Objec
 	}
 
 	private void writeField(String fieldName, Object fieldValue, StringBuilder sb) {
-		sb.append(fieldName);
-		sb.append(':');
-		sb.append(fieldValue.toString());
-		sb.append("\n");
+		sb.append(fieldName).append(':').append(fieldValue).append("\n");
 	}
 
 	private DataBuffer encodeText(CharSequence text, MediaType mediaType, DataBufferFactory bufferFactory) {
 		Assert.notNull(mediaType.getCharset(), "Expected MediaType with charset");
 		byte[] bytes = text.toString().getBytes(mediaType.getCharset());
-		return bufferFactory.wrap(bytes); // wrapping, not allocating
+		return bufferFactory.wrap(bytes);  // wrapping, not allocating
 	}
 
 	@Override