Document default charset in Jackson message converters Javadoc

Issue: SPR-13600

spring-messaging/src/main/java/org/springframework/messaging/converter/MappingJackson2MessageConverter.java

@@ -71,7 +71,7 @@ public class MappingJackson2MessageConverter extends AbstractMessageConverter {
 
 	/**
 	 * Construct a {@code MappingJackson2MessageConverter} supporting
-	 * the {@code application/json} MIME type.
+	 * the {@code application/json} MIME type with {@code UTF-8} character set.
 	 */
 	public MappingJackson2MessageConverter() {
 		super(new MimeType("application", "json", Charset.forName("UTF-8")));

spring-web/src/main/java/org/springframework/http/converter/json/MappingJackson2HttpMessageConverter.java

@@ -29,7 +29,8 @@ import org.springframework.http.MediaType;
  *
  * <p>This converter can be used to bind to typed beans, or untyped {@link java.util.HashMap HashMap} instances.
  *
- * <p>By default, this converter supports {@code application/json} and {@code application/*+json}.
+ * <p>By default, this converter supports {@code application/json} and {@code application/*+json}
+ * with {@code UTF-8} character set.
  * This can be overridden by setting the {@link #setSupportedMediaTypes supportedMediaTypes} property.
  *
  * <p>The default constructor uses the default configuration provided by {@link Jackson2ObjectMapperBuilder}.

spring-web/src/main/java/org/springframework/http/converter/xml/MappingJackson2XmlHttpMessageConverter.java

@@ -29,7 +29,8 @@ import org.springframework.util.Assert;
  * that can read and write XML using <a href="https://github.com/FasterXML/jackson-dataformat-xml">
  * Jackson 2.x extension component for reading and writing XML encoded data</a>.
  *
- * <p>By default, this converter supports {@code application/xml}, {@code text/xml}, and {@code application/*+xml}.
+ * <p>By default, this converter supports {@code application/xml}, {@code text/xml}, and
+ * {@code application/*+xml} with {@code UTF-8} character set.
  * This can be overridden by setting the {@link #setSupportedMediaTypes(java.util.List) supportedMediaTypes} property.
  *
  * <p>The default constructor uses the default configuration provided by {@link Jackson2ObjectMapperBuilder}.