Polish Undertow contribution

Closes gh-1779

spring-boot-docs/src/main/asciidoc/cloud-deployment.adoc

@@ -158,8 +158,8 @@ for our starter REST application:
 
 Spring Boot makes `-D` arguments available as properties accessible from a Spring
 `Environment` instance. The `server.port` configuration property is fed to the embedded
-Tomcat or Jetty instance which then uses it when it starts up. The `$PORT` environment
-variable is assigned to us by the Heroku PaaS.
+Tomcat, Jetty or Undertow instance which then uses it when it starts up. The `$PORT`
+environment variable is assigned to us by the Heroku PaaS.
 
 Heroku by default will use Java 1.6. This is fine as long as your Maven or Gradle build
 is set to use the same version (Maven users can use the `java.version` property). If you

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

@@ -556,6 +556,61 @@ of ways. Or the nuclear option is to add your own `JettyEmbeddedServletContainer
 
 
 
+[[howto-use-undertow-instead-of-tomcat]]
+=== Use Undertow instead of Tomcat
+Using Undertow instead of Tomcat is very similar to <<howto-use-jetty-instead-of-tomcat,
+using Jetty instead of Tomcat>>. You need to exclude the Tomcat dependencies and include
+the Undertow starter instead.
+
+Example in Maven:
+
+[source,xml,indent=0,subs="verbatim,quotes,attributes"]
+----
+	<dependency>
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-starter-web</artifactId>
+		<exclusions>
+			<exclusion>
+				<groupId>org.springframework.boot</groupId>
+				<artifactId>spring-boot-starter-tomcat</artifactId>
+			</exclusion>
+		</exclusions>
+	</dependency>
+	<dependency>
+		<groupId>org.springframework.boot</groupId>
+		<artifactId>spring-boot-starter-undertow</artifactId>
+	</dependency>
+----
+
+Example in Gradle:
+
+[source,groovy,indent=0,subs="verbatim,quotes,attributes"]
+----
+	configurations {
+		compile.exclude module: "spring-boot-starter-tomcat"
+	}
+
+	dependencies {
+		compile("org.springframework.boot:spring-boot-starter-web:{spring-boot-version}")
+		compile("org.springframework.boot:spring-boot-starter-undertow:{spring-boot-version}")
+		// ...
+	}
+----
+
+
+[[howto-configure-undertow]]
+=== Configure Undertow
+Generally you can follow the advice from
+_<<howto-discover-build-in-options-for-external-properties>>_ about
+`@ConfigurationProperties` (`ServerProperties` and `ServerProperties.Undertow are the
+main ones here), but also look at
+`EmbeddedServletContainerCustomizer`. Once you have access to the
+`UndertowEmbeddedServletContainerFactory` you can use an `UndertowBuilderCustomizer` to
+modify Undertow's configuration to meet your needs. Or the nuclear option is to add your
+own `UndertowEmbeddedServletContainerFactory`.
+
+
+
 [[howto-use-tomcat-8]]
 === Use Tomcat 8
 Tomcat 8 works with Spring Boot, but the default is to use Tomcat 7 (so we can support

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

@@ -810,8 +810,8 @@ possible.
 [[boot-features-developing-web-applications]]
 == Developing web applications
 Spring Boot is well suited for web application development. You can easily create a
-self-contained HTTP server using embedded Tomcat or Jetty. Most web applications will
-use the `spring-boot-starter-web` module to get up and running quickly.
+self-contained HTTP server using embedded Tomcat, Jetty, or Undertow. Most web
+applications will use the `spring-boot-starter-web` module to get up and running quickly.
 
 If you haven't yet developed a Spring Boot web application you can follow the
 "Hello World!" example in the
@@ -1093,9 +1093,9 @@ asks for them to be scanned in its `Filter` registration).
 
 [[boot-features-embedded-container]]
 === Embedded servlet container support
-Spring Boot includes support for embedded Tomcat and Jetty servers. Most developers will
-simply use the appropriate '`Starter POM`' to obtain a fully configured instance. By
-default both Tomcat and Jetty will listen for HTTP requests on port `8080`.
+Spring Boot includes support for embedded Tomcat, Jetty, and Undertow servers. Most
+developers will simply use the appropriate '`Starter POM`' to obtain a fully configured
+instance. By default the embedded server will listen for HTTP requests on port `8080`.
 
 
 
@@ -1121,8 +1121,9 @@ interface.
 Under the hood Spring Boot uses a new type of `ApplicationContext` for embedded
 servlet container support.  The `EmbeddedWebApplicationContext` is a special
 type of `WebApplicationContext` that bootstraps itself by searching for a single
-`EmbeddedServletContainerFactory` bean. Usually a `TomcatEmbeddedServletContainerFactory`
-or `JettyEmbeddedServletContainerFactory` will have been auto-configured.
+`EmbeddedServletContainerFactory` bean. Usually a `TomcatEmbeddedServletContainerFactory`,
+`JettyEmbeddedServletContainerFactory`, or `UndertowEmbeddedServletContainerFactory` will
+have been auto-configured.
 
 NOTE: You usually won't need to be aware of these implementation classes. Most
 applications will be auto-configured and the appropriate `ApplicationContext` and
@@ -1176,8 +1177,8 @@ methods.
 [[boot-features-customizing-configurableembeddedservletcontainerfactory-directly]]
 ===== Customizing ConfigurableEmbeddedServletContainer directly
 If the above customization techniques are too limited, you can register the
-`TomcatEmbeddedServletContainerFactory` or `JettyEmbeddedServletContainerFactory` bean
-yourself.
+`TomcatEmbeddedServletContainerFactory`, `JettyEmbeddedServletContainerFactory` or
+`UndertowEmbeddedServletContainerFactory` bean yourself.
 
 [source,java,indent=0]
 ----
@@ -1208,6 +1209,8 @@ packaged as an executable archive), there are some limitations in the JSP suppor
 
 * Jetty does not currently work as an embedded container with JSPs.
 
+* Undertow does not support JSPs
+
 There is a {github-code}/spring-boot-samples/spring-boot-sample-web-jsp[JSP sample] so
 you can see how to set things up.
 

spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc

@@ -348,6 +348,9 @@ swap specific technical facets.
 
 |`spring-boot-starter-tomcat`
 |Import Spring Boot's default HTTP engine (Tomcat).
+
+|`spring-boot-starter-undertow`
+|Imports the Undertow HTTP engine (to be used as an alternative to Tomcat)
 |===
 
 TIP: For a list of additional community contributed starter POMs, see the