Add support for "application/jsonl" JSON lines

Prior to this commit, Spring web frameworks were using the
"application/x-ndjson" media type for streaming JSON payloads delimited
with newlines.

The "application/jsonl" media type seems to gain popularity in the
broader ecosystem and could supersede NDJSON in the future. This commit
adds support for JSON Lines as an alternative.

Closes gh-36485

spring-web/src/main/java/org/springframework/http/MediaType.java

@@ -209,6 +209,19 @@ public class MediaType extends MimeType implements Serializable {
 	 */
 	public static final String APPLICATION_NDJSON_VALUE = "application/x-ndjson";
 
+	/**
+	 * Media type for {@code application/jsonl} (JSON Lines).
+	 * @since 7.1
+	 * @see <a href="https://jsonlines.org/">JSON Lines</a>
+	 */
+	public static final MediaType APPLICATION_JSONL;
+
+	/**
+	 * A String equivalent of {@link MediaType#APPLICATION_JSONL}.
+	 * @since 7.1
+	 */
+	public static final String APPLICATION_JSONL_VALUE = "application/jsonl";
+
 	/**
 	 * Media type for {@code application/xhtml+xml}.
 	 */
@@ -372,6 +385,7 @@ public class MediaType extends MimeType implements Serializable {
 		APPLICATION_GRAPHQL_RESPONSE = new MediaType("application", "graphql-response+json");
 		APPLICATION_JSON = new MediaType("application", "json");
 		APPLICATION_NDJSON = new MediaType("application", "x-ndjson");
+		APPLICATION_JSONL = new MediaType("application", "jsonl");
 		APPLICATION_OCTET_STREAM = new MediaType("application", "octet-stream");
 		APPLICATION_PDF = new MediaType("application", "pdf");
 		APPLICATION_PROBLEM_JSON = new MediaType("application", "problem+json");

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

@@ -58,7 +58,8 @@ public class GsonEncoder extends AbstractEncoder<Object> implements HttpMessageE
 	private static final MimeType[] DEFAULT_JSON_MIME_TYPES = new MimeType[] {
 			MediaType.APPLICATION_JSON,
 			new MediaType("application", "*+json"),
-			MediaType.APPLICATION_NDJSON
+			MediaType.APPLICATION_NDJSON,
+			MediaType.APPLICATION_JSONL
 	};
 
 	private final Gson gson;
@@ -68,11 +69,12 @@ public class GsonEncoder extends AbstractEncoder<Object> implements HttpMessageE
 	/**
 	 * Construct a new encoder using a default {@link Gson} instance
 	 * and the {@code "application/json"} and {@code "application/*+json"}
-	 * MIME types. The {@code "application/x-ndjson"} is configured for streaming.
+	 * MIME types. The {@code "application/jsonl"} and {@code "application/x-ndjson"}
+	 * are configured for streaming.
 	 */
 	public GsonEncoder() {
 		this(new Gson(), DEFAULT_JSON_MIME_TYPES);
-		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON));
+		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON, MediaType.APPLICATION_JSONL));
 	}
 
 	/**

spring-web/src/main/java/org/springframework/http/codec/json/Jackson2CodecSupport.java

@@ -81,7 +81,8 @@ public abstract class Jackson2CodecSupport {
 	private static final List<MimeType> defaultMimeTypes = List.of(
 			MediaType.APPLICATION_JSON,
 			new MediaType("application", "*+json"),
-			MediaType.APPLICATION_NDJSON);
+			MediaType.APPLICATION_NDJSON,
+			MediaType.APPLICATION_JSONL);
 
 
 	protected final Log logger = HttpLogging.forLogName(getClass());

spring-web/src/main/java/org/springframework/http/codec/json/Jackson2JsonEncoder.java

@@ -63,7 +63,7 @@ public class Jackson2JsonEncoder extends AbstractJackson2Encoder {
 
 	public Jackson2JsonEncoder(ObjectMapper mapper, MimeType... mimeTypes) {
 		super(mapper, mimeTypes);
-		setStreamingMediaTypes(Arrays.asList(MediaType.APPLICATION_NDJSON));
+		setStreamingMediaTypes(Arrays.asList(MediaType.APPLICATION_NDJSON, MediaType.APPLICATION_JSONL));
 		this.ssePrettyPrinter = initSsePrettyPrinter();
 	}
 

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

@@ -55,7 +55,8 @@ public class JacksonJsonDecoder extends AbstractJacksonDecoder<JsonMapper> {
 	private static final MimeType[] DEFAULT_JSON_MIME_TYPES = new MimeType[] {
 			MediaType.APPLICATION_JSON,
 			new MediaType("application", "*+json"),
-			MediaType.APPLICATION_NDJSON
+			MediaType.APPLICATION_NDJSON,
+			MediaType.APPLICATION_JSONL
 	};
 
 

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

@@ -55,7 +55,8 @@ public class JacksonJsonEncoder extends AbstractJacksonEncoder<JsonMapper> {
 	private static final MimeType[] DEFAULT_JSON_MIME_TYPES = new MimeType[] {
 			MediaType.APPLICATION_JSON,
 			new MediaType("application", "*+json"),
-			MediaType.APPLICATION_NDJSON
+			MediaType.APPLICATION_NDJSON,
+			MediaType.APPLICATION_JSONL
 	};
 
 
@@ -99,7 +100,7 @@ public class JacksonJsonEncoder extends AbstractJacksonEncoder<JsonMapper> {
 	 */
 	public JacksonJsonEncoder(JsonMapper.Builder builder, MimeType... mimeTypes) {
 		super(builder.addMixIn(ProblemDetail.class, ProblemDetailJacksonMixin.class), mimeTypes);
-		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON));
+		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON, MediaType.APPLICATION_JSONL));
 		this.ssePrettyPrinter = initSsePrettyPrinter();
 	}
 
@@ -110,7 +111,7 @@ public class JacksonJsonEncoder extends AbstractJacksonEncoder<JsonMapper> {
 	 */
 	public JacksonJsonEncoder(JsonMapper mapper, MimeType... mimeTypes) {
 		super(mapper, mimeTypes);
-		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON));
+		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON, MediaType.APPLICATION_JSONL));
 		this.ssePrettyPrinter = initSsePrettyPrinter();
 	}
 

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

@@ -56,7 +56,8 @@ public class KotlinSerializationJsonDecoder extends KotlinSerializationStringDec
 	private static final MimeType[] DEFAULT_JSON_MIME_TYPES = new MimeType[] {
 			MediaType.APPLICATION_JSON,
 			new MediaType("application", "*+json"),
-			MediaType.APPLICATION_NDJSON
+			MediaType.APPLICATION_NDJSON,
+			MediaType.APPLICATION_JSONL
 	};
 
 	/**

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

@@ -36,7 +36,7 @@ import org.springframework.util.MimeType;
 /**
  * Encode from an {@code Object} stream to a byte stream of JSON objects using
  * <a href="https://github.com/Kotlin/kotlinx.serialization">kotlinx.serialization</a>.
- * It supports {@code application/json}, {@code application/x-ndjson} and {@code application/*+json} with
+ * It supports {@code application/json}, {@code application/x-ndjson}, {@code application/jsonl} and {@code application/*+json} with
  * various character sets, {@code UTF-8} being the default.
  *
  * <p>As of Spring Framework 7.0, by default it only encodes types annotated with
@@ -59,7 +59,8 @@ public class KotlinSerializationJsonEncoder extends KotlinSerializationStringEnc
 	private static final MimeType[] DEFAULT_JSON_MIME_TYPES = new MimeType[] {
 			MediaType.APPLICATION_JSON,
 			new MediaType("application", "*+json"),
-			MediaType.APPLICATION_NDJSON
+			MediaType.APPLICATION_NDJSON,
+			MediaType.APPLICATION_JSONL
 	};
 
 	/**
@@ -87,7 +88,7 @@ public class KotlinSerializationJsonEncoder extends KotlinSerializationStringEnc
 	 */
 	public KotlinSerializationJsonEncoder(Json json) {
 		super(json, DEFAULT_JSON_MIME_TYPES);
-		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON));
+		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON, MediaType.APPLICATION_JSONL));
 	}
 
 	/**
@@ -97,7 +98,7 @@ public class KotlinSerializationJsonEncoder extends KotlinSerializationStringEnc
 	 */
 	public KotlinSerializationJsonEncoder(Json json, Predicate<ResolvableType> typePredicate) {
 		super(json, typePredicate, DEFAULT_JSON_MIME_TYPES);
-		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON));
+		setStreamingMediaTypes(List.of(MediaType.APPLICATION_NDJSON, MediaType.APPLICATION_JSONL));
 	}
 
 	@Override

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

@@ -80,7 +80,7 @@ public class ProtobufJsonEncoder implements HttpMessageEncoder<Message> {
 
 	@Override
 	public List<MediaType> getStreamingMediaTypes() {
-		return List.of(MediaType.APPLICATION_NDJSON);
+		return List.of(MediaType.APPLICATION_NDJSON, MediaType.APPLICATION_JSONL);
 	}
 
 	@Override