Raise the minimum supported version of Gradle to 3.4

Closes spring-projectsgh-7922

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -78,7 +78,7 @@
 		<freemarker.version>2.3.25-incubating</freemarker.version>
 		<elasticsearch.version>2.4.4</elasticsearch.version>
 		<glassfish-el.version>3.0.0</glassfish-el.version>
-		<gradle.version>2.9</gradle.version>
+		<gradle.version>3.4</gradle.version>
 		<groovy.version>2.4.9</groovy.version>
 		<gson.version>2.8.0</gson.version>
 		<h2.version>1.4.193</h2.version>

spring-boot-docs/src/main/asciidoc/getting-started.adoc

@@ -38,7 +38,7 @@ diverge from the defaults.
 == System Requirements
 Spring Boot {spring-boot-version} requires http://www.java.com[Java 8] and Spring
 Framework {spring-version} or above. Explicit build support is provided for Maven
-(3.2+), and Gradle 2 (2.9 or later) and 3.
+(3.2+), and Gradle 3 (3.4 or later).
 
 
 [[getting-started-system-requirements-servlet-containers]]
@@ -184,8 +184,8 @@ scope.
 
 [[getting-started-gradle-installation]]
 ==== Gradle installation
-Spring Boot is compatible with Gradle 2 (2.9 or later) and Gradle 3. If you don't already
-have Gradle installed you can follow the instructions at http://www.gradle.org/.
+Spring Boot is compatible with Gradle 3 (3.4 or later). If you don't already have Gradle
+installed you can follow the instructions at http://www.gradle.org/.
 
 Spring Boot dependencies can be declared using the `org.springframework.boot` `group`.
 Typically your project will declare dependencies to one or more

spring-boot-integration-tests/spring-boot-gradle-tests/src/test/java/org/springframework/boot/gradle/InstallTests.java

@@ -38,11 +38,9 @@ public void cleanInstall() throws Exception {
 	}
 
 	@Test
-	public void cleanInstallApp() throws Exception {
+	public void cleanInstallDist() throws Exception {
 		this.project = new ProjectCreator().createProject("install-app");
-		// "install" from the application plugin was renamed "installApp" in Gradle
-		// 1.0
-		this.project.newBuild().forTasks("installApp")
+		this.project.newBuild().forTasks("installDist")
 				.withArguments("-PbootVersion=" + BOOT_VERSION, "--stacktrace").run();
 	}
 

spring-boot-integration-tests/spring-boot-gradle-tests/src/test/java/org/springframework/boot/gradle/ProjectCreator.java

@@ -34,7 +34,7 @@ public class ProjectCreator {
 	private String gradleVersion;
 
 	public ProjectCreator() {
-		this("2.9");
+		this("3.4");
 	}
 
 	public ProjectCreator(String gradleVersion) {

spring-boot-parent/pom.xml

@@ -234,6 +234,11 @@
 				<artifactId>gradle-plugins</artifactId>
 				<version>${gradle.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.gradle</groupId>
+				<artifactId>gradle-process-services</artifactId>
+				<version>${gradle.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.jetbrains.kotlin</groupId>
 				<artifactId>kotlin-runtime</artifactId>

spring-boot-tools/spring-boot-gradle-plugin/pom.xml

@@ -63,6 +63,11 @@
 			<artifactId>gradle-plugins</artifactId>
 			<scope>provided</scope>
 		</dependency>
+		<dependency>
+			<groupId>org.gradle</groupId>
+			<artifactId>gradle-process-services</artifactId>
+			<scope>provided</scope>
+		</dependency>
 	</dependencies>
 	<repositories>
 		<repository>