Append "data:" after line breaks for SSE JSON data fields

Issue: SPR-14899

Author: sdeleuze

spring-web/src/main/java/org/springframework/http/converter/json/AbstractJackson2HttpMessageConverter.java

@@ -26,11 +26,14 @@
 import com.fasterxml.jackson.core.JsonEncoding;
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.core.PrettyPrinter;
+import com.fasterxml.jackson.core.util.DefaultIndenter;
 import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
 import com.fasterxml.jackson.databind.JavaType;
 import com.fasterxml.jackson.databind.JsonMappingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.ObjectWriter;
+import com.fasterxml.jackson.databind.SerializationConfig;
 import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.databind.ser.FilterProvider;
 import com.fasterxml.jackson.databind.type.TypeFactory;
@@ -63,27 +66,36 @@ public abstract class AbstractJackson2HttpMessageConverter extends AbstractGener
 
 	public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
 
+	private static final MediaType TEXT_EVENT_STREAM = new MediaType("text", "event-stream");
+
 
 	protected ObjectMapper objectMapper;
 
 	private Boolean prettyPrint;
 
+	private PrettyPrinter ssePrettyPrinter;
+
 
 	protected AbstractJackson2HttpMessageConverter(ObjectMapper objectMapper) {
-		this.objectMapper = objectMapper;
-		setDefaultCharset(DEFAULT_CHARSET);
+		init(objectMapper);
 	}
 
 	protected AbstractJackson2HttpMessageConverter(ObjectMapper objectMapper, MediaType supportedMediaType) {
 		super(supportedMediaType);
-		this.objectMapper = objectMapper;
-		setDefaultCharset(DEFAULT_CHARSET);
+		init(objectMapper);
 	}
 
 	protected AbstractJackson2HttpMessageConverter(ObjectMapper objectMapper, MediaType... supportedMediaTypes) {
 		super(supportedMediaTypes);
+		init(objectMapper);
+	}
+
+	protected void init(ObjectMapper objectMapper) {
 		this.objectMapper = objectMapper;
 		setDefaultCharset(DEFAULT_CHARSET);
+		DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
+		prettyPrinter.indentObjectsWith(new DefaultIndenter("  ", "\ndata:"));
+		this.ssePrettyPrinter = prettyPrinter;
 	}
 
 
@@ -233,7 +245,8 @@ private Object readJavaType(JavaType javaType, HttpInputMessage inputMessage) {
 	protected void writeInternal(Object object, Type type, HttpOutputMessage outputMessage)
 			throws IOException, HttpMessageNotWritableException {
 
-		JsonEncoding encoding = getJsonEncoding(outputMessage.getHeaders().getContentType());
+		MediaType contentType = outputMessage.getHeaders().getContentType();
+		JsonEncoding encoding = getJsonEncoding(contentType);
 		JsonGenerator generator = this.objectMapper.getFactory().createGenerator(outputMessage.getBody(), encoding);
 		try {
 			writePrefix(generator, object);
@@ -264,6 +277,11 @@ else if (filters != null) {
 			if (javaType != null && javaType.isContainerType()) {
 				objectWriter = objectWriter.forType(javaType);
 			}
+			SerializationConfig config = objectWriter.getConfig();
+			if (contentType != null && contentType.isCompatibleWith(TEXT_EVENT_STREAM) &&
+					config.isEnabled(SerializationFeature.INDENT_OUTPUT)) {
+				objectWriter = objectWriter.with(this.ssePrettyPrinter);
+			}
 			objectWriter.writeValue(generator, value);
 
 			writeSuffix(generator, object);

spring-web/src/test/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverterTests.java

@@ -225,6 +225,20 @@ public void prettyPrint() throws Exception {
 		assertEquals("{" + NEWLINE_SYSTEM_PROPERTY + "  \"name\" : \"Jason\"" + NEWLINE_SYSTEM_PROPERTY + "}", result);
 	}
 
+	@Test
+	public void prettyPrintWithSse() throws Exception {
+		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();
+		outputMessage.getHeaders().setContentType(new MediaType("text", "event-stream"));
+		PrettyPrintBean bean = new PrettyPrintBean();
+		bean.setName("Jason");
+
+		this.converter.setPrettyPrint(true);
+		this.converter.writeInternal(bean, null, outputMessage);
+		String result = outputMessage.getBodyAsString(Charset.forName("UTF-8"));
+
+		assertEquals("{\ndata:  \"name\" : \"Jason\"\ndata:}", result);
+	}
+
 	@Test
 	public void prefixJson() throws Exception {
 		MockHttpOutputMessage outputMessage = new MockHttpOutputMessage();