Locate additional metadata when using Gradle 4

Closes gh-9758

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/MetadataStore.java

@@ -110,18 +110,34 @@ public class MetadataStore {
 
 	private InputStream getAdditionalMetadataStream() throws IOException {
 		// Most build systems will have copied the file to the class output location
-		FileObject fileObject = this.environment.getFiler()
-				.getResource(StandardLocation.CLASS_OUTPUT, "", ADDITIONAL_METADATA_PATH);
+		FileObject fileObject = this.environment.getFiler().getResource(StandardLocation.CLASS_OUTPUT, "", ADDITIONAL_METADATA_PATH);
+				
 		File file = new File(fileObject.toUri());
+
 		if (!file.exists()) {
 			// Gradle keeps things separate
 			String path = file.getPath();
+
 			int index = path.lastIndexOf(CLASSES_FOLDER);
 			if (index >= 0) {
-				path = path.substring(0, index) + RESOURCES_FOLDER
-						+ path.substring(index + CLASSES_FOLDER.length());
-				file = new File(path);
+				/*
+					Gradle 4 introduces a new 'java' directory which causes issues for one-to-one path mapping
+					of class locations and resources. Ensure resources can be found under '/build/resources/main'
+					rather than '/build/resources/java/main'.
+				 */
+				final String pathBeforeClassFolder = path.substring(0, index);
+				/*
+				In order to retrieve the the class output resource, we MUST pass in a relative path.
+				An empty path causes a InvalidArgumentException as it must be resolvable. In reality,
+				this means nothing since we are going to traverse upstream to its parent to locate
+				the 'main' directory.
+				 */
+				FileObject classOutputLocation = this.environment.getFiler().getResource(StandardLocation.CLASS_OUTPUT, "", "dummy");
+				File classesFolder = new File(classOutputLocation.toUri());
+				File resourcesFolder = new File(pathBeforeClassFolder + RESOURCES_FOLDER + '/' + classesFolder.getParentFile().getName());
+				file = new File(resourcesFolder, ADDITIONAL_METADATA_PATH);
 			}
+
 		}
 		return (file.exists() ? new FileInputStream(file)
 				: fileObject.toUri().toURL().openStream());