/*
 * Copyright 2012-2019 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.web.embedded.tomcat;

import java.io.IOException;
import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;

import org.apache.catalina.loader.ParallelWebappClassLoader;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.tomcat.util.compat.JreCompat;

Extension of Tomcat's ParallelWebappClassLoader that does not consider the system classloader. This is required to ensure that any custom context class loader is always used (as is the case with some executable archives). 
Author:
Phillip Webb, Andy Clement
Since:
2.0.0/**
 * Extension of Tomcat's {@link ParallelWebappClassLoader} that does not consider the
 * {@link ClassLoader#getSystemClassLoader() system classloader}. This is required to
 * ensure that any custom context class loader is always used (as is the case with some
 * executable archives).
 *
 * @author Phillip Webb
 * @author Andy Clement
 * @since 2.0.0
 */
public class TomcatEmbeddedWebappClassLoader extends ParallelWebappClassLoader {

	private static final Log logger = LogFactory.getLog(TomcatEmbeddedWebappClassLoader.class);

	static {
		if (!JreCompat.isGraalAvailable()) {
			ClassLoader.registerAsParallelCapable();
		}
	}

	public TomcatEmbeddedWebappClassLoader() {
	}

	public TomcatEmbeddedWebappClassLoader(ClassLoader parent) {
		super(parent);
	}

	@Override
	public URL findResource(String name) {
		return null;
	}

	@Override
	public Enumeration<URL> findResources(String name) throws IOException {
		return Collections.emptyEnumeration();
	}

	@Override
	public Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
		synchronized (JreCompat.isGraalAvailable() ? this : getClassLoadingLock(name)) {
			Class<?> result = findExistingLoadedClass(name);
			result = (result != null) ? result : doLoadClass(name);
			if (result == null) {
				throw new ClassNotFoundException(name);
			}
			return resolveIfNecessary(result, resolve);
		}
	}

	private Class<?> findExistingLoadedClass(String name) {
		Class<?> resultClass = findLoadedClass0(name);
		resultClass = (resultClass != null || JreCompat.isGraalAvailable()) ? resultClass : findLoadedClass(name);
		return resultClass;
	}

	private Class<?> doLoadClass(String name) throws ClassNotFoundException {
		checkPackageAccess(name);
		if ((this.delegate || filter(name, true))) {
			Class<?> result = loadFromParent(name);
			return (result != null) ? result : findClassIgnoringNotFound(name);
		}
		Class<?> result = findClassIgnoringNotFound(name);
		return (result != null) ? result : loadFromParent(name);
	}

	private Class<?> resolveIfNecessary(Class<?> resultClass, boolean resolve) {
		if (resolve) {
			resolveClass(resultClass);
		}
		return (resultClass);
	}

	@Override
	protected void addURL(URL url) {
		// Ignore URLs added by the Tomcat 8 implementation (see gh-919)
		if (logger.isTraceEnabled()) {
			logger.trace("Ignoring request to add " + url + " to the tomcat classloader");
		}
	}

	private Class<?> loadFromParent(String name) {
		if (this.parent == null) {
			return null;
		}
		try {
			return Class.forName(name, false, this.parent);
		}
		catch (ClassNotFoundException ex) {
			return null;
		}
	}

	private Class<?> findClassIgnoringNotFound(String name) {
		try {
			return findClass(name);
		}
		catch (ClassNotFoundException ex) {
			return null;
		}
	}

	private void checkPackageAccess(String name) throws ClassNotFoundException {
		if (this.securityManager != null && name.lastIndexOf('.') >= 0) {
			try {
				this.securityManager.checkPackageAccess(name.substring(0, name.lastIndexOf('.')));
			}
			catch (SecurityException ex) {
				throw new ClassNotFoundException("Security Violation, attempt to use Restricted Class: " + name, ex);
			}
		}
	}

}