Port the build to Gradle

Closes gh-1457

gradle/plugins/optional-dependencies-plugin/build.gradle

@@ -0,0 +1,23 @@
+plugins {
+	id "checkstyle"
+	id "java-gradle-plugin"
+	id "io.spring.javaformat" version "$javaFormatVersion"
+}
+
+repositories {
+	mavenCentral()
+}
+
+dependencies {
+	checkstyle("com.puppycrawl.tools:checkstyle:${checkstyle.toolVersion}")
+	checkstyle("io.spring.javaformat:spring-javaformat-checkstyle:${javaFormatVersion}")
+}
+
+gradlePlugin {
+	plugins {
+		optionalDependenciesPlugin {
+			id = "org.springframework.ws.optional-dependencies"
+			implementationClass = "org.springframework.ws.gradle.optional.OptionalDependenciesPlugin"
+		}
+	}
+}

gradle/plugins/optional-dependencies-plugin/src/main/java/org/springframework/ws/gradle/optional/OptionalDependenciesPlugin.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2005-2025 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.ws.gradle.optional;
+
+import org.gradle.api.Plugin;
+import org.gradle.api.Project;
+import org.gradle.api.artifacts.ConfigurationContainer;
+import org.gradle.api.plugins.JavaPlugin;
+import org.gradle.api.plugins.JavaPluginExtension;
+
+/**
+ * Plugin that adds support for "optional" dependencies. An optional dependency is
+ * available for compilation and at runtime when building and testing the project but is
+ * not exposed to consumers.
+ *
+ * @author Andy Wilkinson
+ */
+public class OptionalDependenciesPlugin implements Plugin<Project> {
+
+	@Override
+	public void apply(Project target) {
+		target.getPlugins().withType(JavaPlugin.class, (plugin) -> {
+			ConfigurationContainer configurations = target.getConfigurations();
+			configurations.create("optional", (optional) -> {
+				optional.setCanBeConsumed(false);
+				optional.setCanBeResolved(false);
+				target.getExtensions().getByType(JavaPluginExtension.class).getSourceSets().all((sourceSet) -> {
+					configurations.getByName(sourceSet.getCompileClasspathConfigurationName()).extendsFrom(optional);
+					configurations.getByName(sourceSet.getRuntimeClasspathConfigurationName()).extendsFrom(optional);
+				});
+			});
+		});
+	}
+
+}

gradle/plugins/optional-dependencies-plugin/src/main/java/org/springframework/ws/gradle/optional/package-info.java

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2005-2025 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.
+ */
+
+/**
+ * Support for optional dependencies in a Gradle build.
+ */
+package org.springframework.ws.gradle.optional;