Merge branch '2.3.x'

Closes gh-23816

spring-boot-project/spring-boot-docs/src/docs/asciidoc/howto.adoc

@@ -597,29 +597,12 @@ This support depends on the chosen web server and the application environment, s
 
 [NOTE]
 ====
-Spring Boot does not support `h2c`, the cleartext version of the HTTP/2 protocol.
-So you must <<howto-configure-ssl, configure SSL first>>.
+Spring Boot does not advise using `h2c`, the cleartext version of the HTTP/2 protocol.
+As a result, the next sections require to <<howto-configure-ssl, configure SSL first>>.
+If you still choose to use `h2c`, you can check <<howto-configure-http2-h2c, the dedicated section>>.
 ====
 
 
-
-[[howto-configure-http2-undertow]]
-==== HTTP/2 with Undertow
-As of Undertow 1.4.0+, HTTP/2 is supported without any additional requirement on JDK8.
-
-
-
-[[howto-configure-http2-jetty]]
-==== HTTP/2 with Jetty
-For HTTP/2 support, Jetty requires the additional `org.eclipse.jetty.http2:http2-server` dependency.
-Now depending on your deployment, you also need to choose other dependencies:
-
-* `org.eclipse.jetty:jetty-alpn-java-server` for applications running on JDK9+
-* `org.eclipse.jetty:jetty-alpn-openjdk8-server` for applications running on JDK8u252+
-* `org.eclipse.jetty:jetty-alpn-conscrypt-server` and the https://www.conscrypt.org/[Conscrypt library] with no JDK requirement
-
-
-
 [[howto-configure-http2-tomcat]]
 ==== HTTP/2 with Tomcat
 Spring Boot ships by default with Tomcat 9.0.x which supports HTTP/2 out of the box when using JDK 9 or later.
@@ -639,6 +622,16 @@ Starting Tomcat 9.0.x on JDK 8 without that native support logs the following er
 This error is not fatal, and the application still starts with HTTP/1.1 SSL support.
 
 
+[[howto-configure-http2-jetty]]
+==== HTTP/2 with Jetty
+For HTTP/2 support, Jetty requires the additional `org.eclipse.jetty.http2:http2-server` dependency.
+Now depending on your deployment, you also need to choose other dependencies:
+
+* `org.eclipse.jetty:jetty-alpn-java-server` for applications running on JDK9+
+* `org.eclipse.jetty:jetty-alpn-openjdk8-server` for applications running on JDK8u252+
+* `org.eclipse.jetty:jetty-alpn-conscrypt-server` and the https://www.conscrypt.org/[Conscrypt library] with no JDK requirement
+
+
 
 [[howto-configure-http2-netty]]
 ==== HTTP/2 with Reactor Netty
@@ -652,6 +645,71 @@ Developers can choose to import only the required dependencies using a classifie
 
 
 
+[[howto-configure-http2-undertow]]
+==== HTTP/2 with Undertow
+As of Undertow 1.4.0+, HTTP/2 is supported without any additional requirement on JDK8.
+
+
+
+[[howto-configure-http2-h2c]]
+==== h2c with supported servers
+To enable `h2c`, you need to leave the configprop:server.http2.enabled[] property set to `false`,
+and instead apply a customizer specific to your choice of server:
+
+For Tomcat, we need to add an upgrade protocol:
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+	@Bean
+	public TomcatConnectorCustomizer connectorCustomizer() {
+		return (connector) -> connector.addUpgradeProtocol(new Http2Protocol());
+	}
+----
+
+For Jetty, we need to add a connection factory to the existing connector:
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+	@Bean
+	public JettyServerCustomizer serverCustomizer() {
+		return (server) -> {
+			HttpConfiguration configuration = new HttpConfiguration();
+			configuration.setSendServerVersion(false);
+			Arrays.stream(server.getConnectors())
+					.filter(connector -> connector instanceof ServerConnector)
+					.map(ServerConnector.class::cast)
+					.forEach(connector -> {
+						connector.addConnectionFactory(new HTTP2CServerConnectionFactory(configuration));
+					});
+		};
+	}
+----
+
+For Netty, we need to add `h2c` as a supported protocol:
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+	@Bean
+	public NettyServerCustomizer serverCustomizer() {
+		return (server) -> server.protocol(HttpProtocol.H2C);
+	}
+----
+
+For Undertow, we need to enable the HTTP2 option:
+
+[source,java,indent=0,subs="verbatim,quotes,attributes"]
+----
+	@Bean
+	public UndertowBuilderCustomizer builderCustomizer() {
+		return (builder) -> {
+			builder.setServerOption(ENABLE_HTTP2, true);
+		};
+	}
+----
+
+
+
+
 [[howto-configure-webserver]]
 === Configure the Web Server
 Generally, you should first consider using one of the many available configuration keys and customize your web server by adding new entries in your `application.properties` (or `application.yml`, or environment, etc. see "`<<howto-discover-build-in-options-for-external-properties>>`").

spring-boot-project/spring-boot-test-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -178,6 +178,7 @@ org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
 org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
 org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
 org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
+org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
 org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration
 
 # AutoConfigureWebServiceClient

spring-boot-project/spring-boot-test-autoconfigure/src/test/java/org/springframework/boot/test/autoconfigure/web/servlet/WebMvcTestAutoConfigurationIntegrationTests.java

@@ -26,6 +26,7 @@ import org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAu
 import org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration;
 import org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration;
 import org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration;
+import org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration;
 import org.springframework.context.ApplicationContext;
 import org.springframework.core.task.AsyncTaskExecutor;
 import org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter;
@@ -88,4 +89,9 @@ class WebMvcTestAutoConfigurationIntegrationTests {
 		assertThat(this.applicationContext).has(importedAutoConfiguration(OAuth2ResourceServerAutoConfiguration.class));
 	}
 
+	@Test
+	void httpEncodingAutoConfigurationWasImported() {
+		assertThat(this.applicationContext).has(importedAutoConfiguration(HttpEncodingAutoConfiguration.class));
+	}
+
 }