Remove support for Gradle 6 and 7

Closes gh-1586

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/build/gradle/GradleProjectGenerationConfiguration.java

@@ -113,7 +113,7 @@ public BuildCustomizer<GradleBuild> warPluginContributor() {
 	}
 
 	@Bean
-	@ConditionalOnGradleVersion({ "6", "7", "8" })
+	@ConditionalOnBuildSystem(id = GradleBuildSystem.ID)
 	BuildCustomizer<GradleBuild> springBootPluginContributor(ProjectDescription description,
 			ObjectProvider<DependencyManagementPluginVersionResolver> versionResolver, InitializrMetadata metadata) {
 		return new SpringBootPluginBuildCustomizer(description, versionResolver
@@ -134,37 +134,6 @@ public GradleBuildProjectContributor gradleKtsBuildProjectContributor(KotlinDslG
 		return new GradleBuildProjectContributor(buildWriter, build, this.indentingWriterFactory, "build.gradle.kts");
 	}
 
-	/**
-	 * Configuration specific to projects using Gradle 6.
-	 *
-	 * @deprecated Gradle 6 support is deprecated
-	 */
-	@Configuration
-	@ConditionalOnGradleVersion("6")
-	@Deprecated
-	static class Gradle6ProjectGenerationConfiguration {
-
-		@Bean
-		GradleWrapperContributor gradle6WrapperContributor() {
-			return new GradleWrapperContributor("6");
-		}
-
-	}
-
-	/**
-	 * Configuration specific to projects using Gradle 7.
-	 */
-	@Configuration
-	@ConditionalOnGradleVersion("7")
-	static class Gradle7ProjectGenerationConfiguration {
-
-		@Bean
-		GradleWrapperContributor gradle7WrapperContributor() {
-			return new GradleWrapperContributor("7");
-		}
-
-	}
-
 	/**
 	 * Configuration specific to projects using Gradle 8.
 	 */
@@ -184,7 +153,6 @@ GradleWrapperContributor gradle8WrapperContributor() {
 	 */
 	@Configuration
 	@ConditionalOnBuildSystem(id = GradleBuildSystem.ID, dialect = GradleBuildSystem.DIALECT_GROOVY)
-	@ConditionalOnGradleVersion({ "6", "7", "8" })
 	static class GradleGroovyProjectGenerationConfiguration {
 
 		@Bean
@@ -218,7 +186,6 @@ GradleAnnotationProcessorScopeBuildCustomizer gradleAnnotationProcessorScopeBuil
 	 */
 	@Configuration
 	@ConditionalOnBuildSystem(id = GradleBuildSystem.ID, dialect = GradleBuildSystem.DIALECT_KOTLIN)
-	@ConditionalOnGradleVersion({ "6", "7", "8" })
 	static class GradleKtsProjectGenerationConfiguration {
 
 		@Bean

initializr-generator-spring/src/main/java/io/spring/initializr/generator/spring/build/gradle/OnGradleVersionCondition.java

@@ -21,8 +21,6 @@
 import io.spring.initializr.generator.condition.ProjectGenerationCondition;
 import io.spring.initializr.generator.project.ProjectDescription;
 import io.spring.initializr.generator.version.Version;
-import io.spring.initializr.generator.version.VersionParser;
-import io.spring.initializr.generator.version.VersionRange;
 
 import org.springframework.context.annotation.ConditionContext;
 import org.springframework.core.type.AnnotatedTypeMetadata;
@@ -36,13 +34,6 @@
  */
 public class OnGradleVersionCondition extends ProjectGenerationCondition {
 
-	private static final VersionRange GRADLE_6_VERSION_RANGE = VersionParser.DEFAULT
-		.parseRange("[2.2.2.RELEASE,2.5.0-RC1)");
-
-	private static final VersionRange GRADLE_7_VERSION_RANGE = VersionParser.DEFAULT.parseRange("[2.5.0-RC1,2.7.10)");
-
-	private static final VersionRange GRADLE_8_VERSION_RANGE = VersionParser.DEFAULT.parseRange("2.7.10");
-
 	@Override
 	protected boolean matches(ProjectDescription description, ConditionContext context,
 			AnnotatedTypeMetadata metadata) {
@@ -59,18 +50,7 @@ private String determineGradleGeneration(Version platformVersion) {
 		if (platformVersion == null) {
 			return null;
 		}
-		else if (GRADLE_6_VERSION_RANGE.match(platformVersion)) {
-			return "6";
-		}
-		else if (GRADLE_7_VERSION_RANGE.match(platformVersion)) {
-			return "7";
-		}
-		else if (GRADLE_8_VERSION_RANGE.match(platformVersion)) {
-			return "8";
-		}
-		else {
-			return null;
-		}
+		return "8";
 	}
 
 }