Improve WebSocket documentation for reactive applications

Closes gh-14069

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -93,6 +93,7 @@
 		<javax-persistence.version>2.2</javax-persistence.version>
 		<javax-transaction.version>1.3</javax-transaction.version>
 		<javax-validation.version>2.0.1.Final</javax-validation.version>
+		<javax-websocket.version>1.1</javax-websocket.version>
 		<jaxen.version>1.1.6</jaxen.version>
 		<jaybird.version>3.0.4</jaybird.version>
 		<jboss-logging.version>3.3.2.Final</jboss-logging.version>
@@ -1069,6 +1070,11 @@
 				<artifactId>validation-api</artifactId>
 				<version>${javax-validation.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>javax.websocket</groupId>
+				<artifactId>javax.websocket-api</artifactId>
+				<version>${javax-websocket.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>javax.xml.bind</groupId>
 				<artifactId>jaxb-api</artifactId>

spring-boot-project/spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -7709,7 +7709,20 @@ Undertow. If you deploy a war file to a standalone container, Spring Boot assume
 container is responsible for the configuration of its WebSocket support.
 
 Spring Framework provides {spring-reference}web.html#websocket[rich WebSocket support]
-that can be easily accessed through the `spring-boot-starter-websocket` module.
+for MVC web applications that can be easily accessed through the
+`spring-boot-starter-websocket` module.
+
+WebSocket support is also available for
+{spring-reference}web-reactive.html#webflux-websocket[reactive web applications] and
+requires to include the WebSocket API alongside `spring-boot-starter-webflux`:
+
+[source,xml,indent=0,subs="verbatim,quotes,attributes"]
+----
+	<dependency>
+		<groupId>javax.websocket</groupId>
+		<artifactId>javax.websocket-api</artifactId>
+	</dependency>
+----