Raise the minimum supported version of Gradle to 8.14 and support 9.x

Closes gh-43573
Closes gh-43574

build-plugin/spring-boot-gradle-plugin/src/docs/antora/modules/gradle-plugin/pages/index.adoc

@@ -3,6 +3,6 @@
 
 The Spring Boot Gradle Plugin provides Spring Boot support in https://gradle.org[Gradle].
 It allows you to package executable jar or war archives, run Spring Boot applications, and use the dependency management provided by `spring-boot-dependencies`.
-Spring Boot's Gradle plugin requires Gradle 7.x (7.6.4 or later) or 8.x (8.4 or later) and can be used with Gradle's {url-gradle-docs}/configuration_cache.html[configuration cache].
+Spring Boot's Gradle plugin requires Gradle 8.x (8.14 or later) or 9.x and can be used with Gradle's {url-gradle-docs}/configuration_cache.html[configuration cache].
 
 In addition to this user guide, xref:api/java/index.html[API documentation] is also available.

build-plugin/spring-boot-gradle-plugin/src/docs/antora/modules/gradle-plugin/pages/introduction.adoc

@@ -3,6 +3,6 @@
 
 The Spring Boot Gradle Plugin provides Spring Boot support in https://gradle.org[Gradle].
 It allows you to package executable jar or war archives, run Spring Boot applications, and use the dependency management provided by `spring-boot-dependencies`.
-Spring Boot's Gradle plugin requires Gradle 7.x (7.6.4 or later) or 8.x (8.4 or later) and can be used with Gradle's {url-gradle-docs}/configuration_cache.html[configuration cache].
+Spring Boot's Gradle plugin requires Gradle 8.x (8.14 or later) or 9.x and can be used with Gradle's {url-gradle-docs}/configuration_cache.html[configuration cache].
 
 In addition to this user guide, xref:api/java/index.html[API documentation] is also available.

build-plugin/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/SpringBootPlugin.java

@@ -20,9 +20,11 @@ import java.util.Arrays;
 import java.util.List;
 import java.util.function.Consumer;
 
+import org.gradle.api.GradleException;
 import org.gradle.api.Plugin;
 import org.gradle.api.Project;
 import org.gradle.api.artifacts.Configuration;
+import org.gradle.util.GradleVersion;
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.boot.gradle.dsl.SpringBootExtension;
@@ -115,11 +117,20 @@ public class SpringBootPlugin implements Plugin<Project> {
 
 	@Override
 	public void apply(Project project) {
+		verifyGradleVersion();
 		createExtension(project);
 		Configuration bootArchives = createBootArchivesConfiguration(project);
 		registerPluginActions(project, bootArchives);
 	}
 
+	private void verifyGradleVersion() {
+		GradleVersion currentVersion = GradleVersion.current();
+		if (currentVersion.compareTo(GradleVersion.version("8.14")) < 0) {
+			throw new GradleException("Spring Boot plugin requires Gradle 8.x (8.14 or later) or 9.x. "
+					+ "The current version is " + currentVersion);
+		}
+	}
+
 	private void createExtension(Project project) {
 		project.getExtensions().create("springBoot", SpringBootExtension.class, project);
 	}

build-plugin/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/SpringBootPluginIntegrationTests.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2012-present the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.gradle.plugin;
+
+import org.gradle.testkit.runner.BuildResult;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.DisabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import org.springframework.boot.gradle.testkit.PluginClasspathGradleBuild;
+import org.springframework.boot.testsupport.BuildOutput;
+import org.springframework.boot.testsupport.gradle.testkit.GradleBuild;
+import org.springframework.boot.testsupport.gradle.testkit.GradleBuildExtension;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for {@link SpringBootPlugin}.
+ *
+ * @author Andy Wilkinson
+ */
+@ExtendWith(GradleBuildExtension.class)
+class SpringBootPluginIntegrationTests {
+
+	final GradleBuild gradleBuild = new PluginClasspathGradleBuild(new BuildOutput(getClass()));
+
+	@Test
+	@DisabledForJreRange(min = JRE.JAVA_24)
+	void failFastWithVersionOfGradle8LowerThanRequired() {
+		BuildResult result = this.gradleBuild.gradleVersion("8.13").buildAndFail();
+		assertThat(result.getOutput()).contains(
+				"Spring Boot plugin requires Gradle 8.x (8.14 or later) or 9.x. The current version is Gradle 8.13");
+	}
+
+}

build-plugin/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/SpringBootPluginIntegrationTests.gradle

@@ -15,5 +15,5 @@
  */
 
 plugins {
-	id 'org.springframework.boot' version '{version}'
+	id 'org.springframework.boot'
 }