Copy FunctionClassUtils to s-c-f-serverless-web

spring-cloud-function-adapters/spring-cloud-function-serverless-web/src/main/java/org/springframework/cloud/function/serverless/web/FunctionClassUtils.java

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2019-2021 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.cloud.function.serverless.web;
+
+import java.io.InputStream;
+import java.net.URL;
+import java.util.Collections;
+import java.util.List;
+import java.util.jar.JarFile;
+import java.util.jar.Manifest;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+//import org.springframework.boot.SpringBootConfiguration;
+//import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.core.KotlinDetector;
+import org.springframework.core.io.Resource;
+import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
+import org.springframework.util.Assert;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.StringUtils;
+
+/**
+ * General utility class which aggregates various class-level utility functions
+ * used by the framework.
+ *
+ * @author Oleg Zhurakousky
+ * @since 3.0.1
+ */
+public final class FunctionClassUtils {
+
+	private static Log logger = LogFactory.getLog(FunctionClassUtils.class);
+
+	private FunctionClassUtils() {
+
+	}
+
+	/**
+	 * Discovers the start class in the currently running application.
+	 * The discover search order is 'MAIN_CLASS' environment property,
+	 * 'MAIN_CLASS' system property, META-INF/MANIFEST.MF:'Start-Class' attribute,
+	 * meta-inf/manifest.mf:'Start-Class' attribute.
+	 *
+	 * @return instance of Class which represent the start class of the application.
+	 */
+	public static Class<?> getStartClass() {
+		ClassLoader classLoader = FunctionClassUtils.class.getClassLoader();
+		return getStartClass(classLoader);
+	}
+
+	static Class<?> getStartClass(ClassLoader classLoader) {
+		Class<?> mainClass = null;
+		if (System.getenv("MAIN_CLASS") != null) {
+			mainClass = ClassUtils.resolveClassName(System.getenv("MAIN_CLASS"), classLoader);
+		}
+		else if (System.getProperty("MAIN_CLASS") != null) {
+			mainClass = ClassUtils.resolveClassName(System.getProperty("MAIN_CLASS"), classLoader);
+		}
+		else {
+			try {
+				Class<?> result = getStartClass(
+						Collections.list(classLoader.getResources(JarFile.MANIFEST_NAME)), classLoader);
+				if (result == null) {
+					result = getStartClass(Collections
+							.list(classLoader.getResources("meta-inf/manifest.mf")), classLoader);
+				}
+				Assert.notNull(result, "Failed to locate main class");
+				mainClass = result;
+			}
+			catch (Exception ex) {
+				throw new IllegalStateException("Failed to discover main class. An attempt was made to discover "
+						+ "main class as 'MAIN_CLASS' environment variable, system property as well as "
+						+ "entry in META-INF/MANIFEST.MF (in that order).", ex);
+			}
+		}
+		logger.info("Main class: " + mainClass);
+		return mainClass;
+	}
+
+	private static Class<?> getStartClass(List<URL> list, ClassLoader classLoader) {
+		if (logger.isTraceEnabled()) {
+			logger.trace("Searching manifests: " + list);
+		}
+		for (URL url : list) {
+			try {
+				InputStream inputStream = null;
+				Manifest manifest = new Manifest(url.openStream());
+				logger.info("Searching for start class in manifest: " + url);
+				if (logger.isDebugEnabled()) {
+					manifest.write(System.out);
+				}
+				try {
+					String startClassName = manifest.getMainAttributes().getValue("Start-Class");
+					if (!StringUtils.hasText(startClassName)) {
+						startClassName = manifest.getMainAttributes().getValue("Main-Class");
+					}
+
+					if (StringUtils.hasText(startClassName)) {
+						Class<?> startClass = ClassUtils.forName(startClassName, classLoader);
+
+						if (KotlinDetector.isKotlinType(startClass)) {
+							PathMatchingResourcePatternResolver r = new PathMatchingResourcePatternResolver(classLoader);
+							String packageName = startClass.getPackage().getName();
+							Resource[] resources = r.getResources("classpath:" + packageName.replace(".", "/") + "/*.class");
+							for (int i = 0; i < resources.length; i++) {
+								Resource resource = resources[i];
+								String className = packageName + "." + (resource.getFilename().replace("/", ".")).replace(".class", "");
+								startClass = ClassUtils.forName(className, classLoader);
+							}
+						}
+					}
+				}
+				finally {
+					if (inputStream != null) {
+						inputStream.close();
+					}
+				}
+			}
+			catch (Exception ex) {
+				logger.debug("Failed to determine Start-Class in manifest file of " + url, ex);
+			}
+		}
+		return null;
+	}
+}