/*
 * Copyright (c) 1997, 2018, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation. Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.net;

import java.io.Closeable;
import java.io.File;
import java.io.FilePermission;
import java.io.IOException;
import java.io.InputStream;
import java.security.AccessControlContext;
import java.security.AccessController;
import java.security.CodeSigner;
import java.security.CodeSource;
import java.security.Permission;
import java.security.PermissionCollection;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;
import java.security.SecureClassLoader;
import java.util.Enumeration;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.Set;
import java.util.WeakHashMap;
import java.util.jar.Attributes;
import java.util.jar.Attributes.Name;
import java.util.jar.JarFile;
import java.util.jar.Manifest;

import jdk.internal.loader.Resource;
import jdk.internal.loader.URLClassPath;
import jdk.internal.access.JavaNetURLClassLoaderAccess;
import jdk.internal.access.SharedSecrets;
import jdk.internal.perf.PerfCounter;
import sun.net.www.ParseUtil;
import sun.security.util.SecurityConstants;

/**
 * This class loader is used to load classes and resources from a search
 * path of URLs referring to both JAR files and directories. Any {@code jar:}
 * scheme URL (see {@link java.net.JarURLConnection}) is assumed to refer to a
 * JAR file. Any {@code file:} scheme URL that ends with a '/' is assumed to
 * refer to a directory. Otherwise, the URL is assumed to refer to a JAR file
 * which will be opened as needed.
 * <p>
 * This class loader supports the loading of classes and resources from the
 * contents of a <a href="../util/jar/JarFile.html#multirelease">multi-release</a>
 * JAR file that is referred to by a given URL.
 * <p>
 * The AccessControlContext of the thread that created the instance of
 * URLClassLoader will be used when subsequently loading classes and
 * resources.
 * <p>
 * The classes that are loaded are by default granted permission only to
 * access the URLs specified when the URLClassLoader was created.
 *
 * @author David Connelly
 * @since 1.2
 */
public class URLClassLoader extends SecureClassLoader implements Closeable {
 /* The search path for classes and resources */
 private final URLClassPath ucp;

 /* The context to be used when loading classes and resources */
 private final AccessControlContext acc;

 /**
 * Constructs a new URLClassLoader for the given URLs. The URLs will be
 * searched in the order specified for classes and resources after first
 * searching in the specified parent class loader. Any {@code jar:}
 * scheme URL is assumed to refer to a JAR file. Any {@code file:} scheme
 * URL that ends with a '/' is assumed to refer to a directory. Otherwise,
 * the URL is assumed to refer to a JAR file which will be downloaded and
 * opened as needed.
 *
 * <p>If there is a security manager, this method first
 * calls the security manager's {@code checkCreateClassLoader} method
 * to ensure creation of a class loader is allowed.
 *
 * @param urls the URLs from which to load classes and resources
 * @param parent the parent class loader for delegation
 * @exception SecurityException if a security manager exists and its
 * {@code checkCreateClassLoader} method doesn't allow
 * creation of a class loader.
 * @exception NullPointerException if {@code urls} or any of its
 * elements is {@code null}.
 * @see SecurityManager#checkCreateClassLoader
 */
 public URLClassLoader(URL[] urls, ClassLoader parent) {
 super(parent);
 this.acc = AccessController.getContext();
 this.ucp = new URLClassPath(urls, acc);
 }

 URLClassLoader(String name, URL[] urls, ClassLoader parent,
 AccessControlContext acc) {
 super(name, parent);
 this.acc = acc;
 this.ucp = new URLClassPath(urls, acc);
 }

 /**
 * Constructs a new URLClassLoader for the specified URLs using the
 * default delegation parent {@code ClassLoader}. The URLs will
 * be searched in the order specified for classes and resources after
 * first searching in the parent class loader. Any URL that ends with
 * a '/' is assumed to refer to a directory. Otherwise, the URL is
 * assumed to refer to a JAR file which will be downloaded and opened
 * as needed.
 *
 * <p>If there is a security manager, this method first
 * calls the security manager's {@code checkCreateClassLoader} method
 * to ensure creation of a class loader is allowed.
 *
 * @param urls the URLs from which to load classes and resources
 *
 * @exception SecurityException if a security manager exists and its
 * {@code checkCreateClassLoader} method doesn't allow
 * creation of a class loader.
 * @exception NullPointerException if {@code urls} or any of its
 * elements is {@code null}.
 * @see SecurityManager#checkCreateClassLoader
 */
 public URLClassLoader(URL[] urls) {
 super();
 this.acc = AccessController.getContext();
 this.ucp = new URLClassPath(urls, acc);
 }

 URLClassLoader(URL[] urls, AccessControlContext acc) {
 super();
 this.acc = acc;
 this.ucp = new URLClassPath(urls, acc);
 }

 /**
 * Constructs a new URLClassLoader for the specified URLs, parent
 * class loader, and URLStreamHandlerFactory. The parent argument
 * will be used as the parent class loader for delegation. The
 * factory argument will be used as the stream handler factory to
 * obtain protocol handlers when creating new jar URLs.
 *
 * <p>If there is a security manager, this method first
 * calls the security manager's {@code checkCreateClassLoader} method
 * to ensure creation of a class loader is allowed.
 *
 * @param urls the URLs from which to load classes and resources
 * @param parent the parent class loader for delegation
 * @param factory the URLStreamHandlerFactory to use when creating URLs
 *
 * @exception SecurityException if a security manager exists and its
 * {@code checkCreateClassLoader} method doesn't allow
 * creation of a class loader.
 * @exception NullPointerException if {@code urls} or any of its
 * elements is {@code null}.
 * @see SecurityManager#checkCreateClassLoader
 */
 public URLClassLoader(URL[] urls, ClassLoader parent,
 URLStreamHandlerFactory factory) {
 super(parent);
 this.acc = AccessController.getContext();
 this.ucp = new URLClassPath(urls, factory, acc);
 }


 /**
 * Constructs a new named {@code URLClassLoader} for the specified URLs.
 * The URLs will be searched in the order specified for classes
 * and resources after first searching in the specified parent class loader.
 * Any URL that ends with a '/' is assumed to refer to a directory.
 * Otherwise, the URL is assumed to refer to a JAR file which will be
 * downloaded and opened as needed.
 *
 * @param name class loader name; or {@code null} if not named
 * @param urls the URLs from which to load classes and resources
 * @param parent the parent class loader for delegation
 *
 * @throws IllegalArgumentException if the given name is empty.
 * @throws NullPointerException if {@code urls} or any of its
 * elements is {@code null}.
 *
 * @throws SecurityException if a security manager exists and its
 * {@link SecurityManager#checkCreateClassLoader()} method doesn't
 * allow creation of a class loader.
 *
 * @since 9
 * @spec JPMS
 */
 public URLClassLoader(String name,
 URL[] urls,
 ClassLoader parent) {
 super(name, parent);
 this.acc = AccessController.getContext();
 this.ucp = new URLClassPath(urls, acc);
 }

 /**
 * Constructs a new named {@code URLClassLoader} for the specified URLs,
 * parent class loader, and URLStreamHandlerFactory.
 * The parent argument will be used as the parent class loader for delegation.
 * The factory argument will be used as the stream handler factory to
 * obtain protocol handlers when creating new jar URLs.
 *
 * @param name class loader name; or {@code null} if not named
 * @param urls the URLs from which to load classes and resources
 * @param parent the parent class loader for delegation
 * @param factory the URLStreamHandlerFactory to use when creating URLs
 *
 * @throws IllegalArgumentException if the given name is empty.
 * @throws NullPointerException if {@code urls} or any of its
 * elements is {@code null}.
 *
 * @throws SecurityException if a security manager exists and its
 * {@code checkCreateClassLoader} method doesn't allow
 * creation of a class loader.
 *
 * @since 9
 * @spec JPMS
 */
 public URLClassLoader(String name, URL[] urls, ClassLoader parent,
 URLStreamHandlerFactory factory) {
 super(name, parent);
 this.acc = AccessController.getContext();
 this.ucp = new URLClassPath(urls, factory, acc);
 }

 /* A map (used as a set) to keep track of closeable local resources
 * (either JarFiles or FileInputStreams). We don't care about
 * Http resources since they don't need to be closed.
 *
 * If the resource is coming from a jar file
 * we keep a (weak) reference to the JarFile object which can
 * be closed if URLClassLoader.close() called. Due to jar file
 * caching there will typically be only one JarFile object
 * per underlying jar file.
 *
 * For file resources, which is probably a less common situation
 * we have to keep a weak reference to each stream.
 */

 private WeakHashMap<Closeable,Void>
 closeables = new WeakHashMap<>();

 /**
 * Returns an input stream for reading the specified resource.
 * If this loader is closed, then any resources opened by this method
 * will be closed.
 *
 * <p> The search order is described in the documentation for {@link
 * #getResource(String)}. </p>
 *
 * @param name
 * The resource name
 *
 * @return An input stream for reading the resource, or {@code null}
 * if the resource could not be found
 *
 * @throws NullPointerException If {@code name} is {@code null}
 *
 * @since 1.7
 */
 public InputStream getResourceAsStream(String name) {
 Objects.requireNonNull(name);
 URL url = getResource(name);
 try {
 if (url == null) {
 return null;
 }
 URLConnection urlc = url.openConnection();
 InputStream is = urlc.getInputStream();
 if (urlc instanceof JarURLConnection) {
 JarURLConnection juc = (JarURLConnection)urlc;
 JarFile jar = juc.getJarFile();
 synchronized (closeables) {
 if (!closeables.containsKey(jar)) {
 closeables.put(jar, null);
 }
 }
 } else if (urlc instanceof sun.net.www.protocol.file.FileURLConnection) {
 synchronized (closeables) {
 closeables.put(is, null);
 }
 }
 return is;
 } catch (IOException e) {
 return null;
 }
 }

 /**
 * Closes this URLClassLoader, so that it can no longer be used to load
 * new classes or resources that are defined by this loader.
 * Classes and resources defined by any of this loader's parents in the
 * delegation hierarchy are still accessible. Also, any classes or resources
 * that are already loaded, are still accessible.
 * <p>
 * In the case of jar: and file: URLs, it also closes any files
 * that were opened by it. If another thread is loading a
 * class when the {@code close} method is invoked, then the result of
 * that load is undefined.
 * <p>
 * The method makes a best effort attempt to close all opened files,
 * by catching {@link IOException}s internally. Unchecked exceptions
 * and errors are not caught. Calling close on an already closed
 * loader has no effect.
 *
 * @exception IOException if closing any file opened by this class loader
 * resulted in an IOException. Any such exceptions are caught internally.
 * If only one is caught, then it is re-thrown. If more than one exception
 * is caught, then the second and following exceptions are added
 * as suppressed exceptions of the first one caught, which is then re-thrown.
 *
 * @exception SecurityException if a security manager is set, and it denies
 * {@link RuntimePermission}{@code ("closeClassLoader")}
 *
 * @since 1.7
 */
 public void close() throws IOException {
 SecurityManager security = System.getSecurityManager();
 if (security != null) {
 security.checkPermission(new RuntimePermission("closeClassLoader"));
 }
 List<IOException> errors = ucp.closeLoaders();

 // now close any remaining streams.

 synchronized (closeables) {
 Set<Closeable> keys = closeables.keySet();
 for (Closeable c : keys) {
 try {
 c.close();
 } catch (IOException ioex) {
 errors.add(ioex);
 }
 }
 closeables.clear();
 }

 if (errors.isEmpty()) {
 return;
 }

 IOException firstex = errors.remove(0);

 // Suppress any remaining exceptions

 for (IOException error: errors) {
 firstex.addSuppressed(error);
 }
 throw firstex;
 }

 /**
 * Appends the specified URL to the list of URLs to search for
 * classes and resources.
 * <p>
 * If the URL specified is {@code null} or is already in the
 * list of URLs, or if this loader is closed, then invoking this
 * method has no effect.
 *
 * @param url the URL to be added to the search path of URLs
 */
 protected void addURL(URL url) {
 ucp.addURL(url);
 }

 /**
 * Returns the search path of URLs for loading classes and resources.
 * This includes the original list of URLs specified to the constructor,
 * along with any URLs subsequently appended by the addURL() method.
 * @return the search path of URLs for loading classes and resources.
 */
 public URL[] getURLs() {
 return ucp.getURLs();
 }

 /**
 * Finds and loads the class with the specified name from the URL search
 * path. Any URLs referring to JAR files are loaded and opened as needed
 * until the class is found.
 *
 * @param name the name of the class
 * @return the resulting class
 * @exception ClassNotFoundException if the class could not be found,
 * or if the loader is closed.
 * @exception NullPointerException if {@code name} is {@code null}.
 */
 protected Class<?> findClass(final String name)
 throws ClassNotFoundException
 {
 final Class<?> result;
 try {
 result = AccessController.doPrivileged(
 new PrivilegedExceptionAction<>() {
 public Class<?> run() throws ClassNotFoundException {
 String path = name.replace('.', '/').concat(".class");
 Resource res = ucp.getResource(path, false);
 if (res != null) {
 try {
 return defineClass(name, res);
 } catch (IOException e) {
 throw new ClassNotFoundException(name, e);
 }
 } else {
 return null;
 }
 }
 }, acc);
 } catch (java.security.PrivilegedActionException pae) {
 throw (ClassNotFoundException) pae.getException();
 }
 if (result == null) {
 throw new ClassNotFoundException(name);
 }
 return result;
 }

 /*
 * Retrieve the package using the specified package name.
 * If non-null, verify the package using the specified code
 * source and manifest.
 */
 private Package getAndVerifyPackage(String pkgname,
 Manifest man, URL url) {
 Package pkg = getDefinedPackage(pkgname);
 if (pkg != null) {
 // Package found, so check package sealing.
 if (pkg.isSealed()) {
 // Verify that code source URL is the same.
 if (!pkg.isSealed(url)) {
 throw new SecurityException(
 "sealing violation: package " + pkgname + " is sealed");
 }
 } else {
 // Make sure we are not attempting to seal the package
 // at this code source URL.
 if ((man != null) && isSealed(pkgname, man)) {
 throw new SecurityException(
 "sealing violation: can't seal package " + pkgname +
 ": already loaded");
 }
 }
 }
 return pkg;
 }

 /*
 * Defines a Class using the class bytes obtained from the specified
 * Resource. The resulting Class must be resolved before it can be
 * used.
 */
 private Class<?> defineClass(String name, Resource res) throws IOException {
 long t0 = System.nanoTime();
 int i = name.lastIndexOf('.');
 URL url = res.getCodeSourceURL();
 if (i != -1) {
 String pkgname = name.substring(0, i);
 // Check if package already loaded.
 Manifest man = res.getManifest();
 if (getAndVerifyPackage(pkgname, man, url) == null) {
 try {
 if (man != null) {
 definePackage(pkgname, man, url);
 } else {
 definePackage(pkgname, null, null, null, null, null, null, null);
 }
 } catch (IllegalArgumentException iae) {
 // parallel-capable class loaders: re-verify in case of a
 // race condition
 if (getAndVerifyPackage(pkgname, man, url) == null) {
 // Should never happen
 throw new AssertionError("Cannot find package " +
 pkgname);
 }
 }
 }
 }
 // Now read the class bytes and define the class
 java.nio.ByteBuffer bb = res.getByteBuffer();
 if (bb != null) {
 // Use (direct) ByteBuffer:
 CodeSigner[] signers = res.getCodeSigners();
 CodeSource cs = new CodeSource(url, signers);
 PerfCounter.getReadClassBytesTime().addElapsedTimeFrom(t0);
 return defineClass(name, bb, cs);
 } else {
 byte[] b = res.getBytes();
 // must read certificates AFTER reading bytes.
 CodeSigner[] signers = res.getCodeSigners();
 CodeSource cs = new CodeSource(url, signers);
 PerfCounter.getReadClassBytesTime().addElapsedTimeFrom(t0);
 return defineClass(name, b, 0, b.length, cs);
 }
 }

 /**
 * Defines a new package by name in this {@code URLClassLoader}.
 * The attributes contained in the specified {@code Manifest}
 * will be used to obtain package version and sealing information.
 * For sealed packages, the additional URL specifies the code source URL
 * from which the package was loaded.
 *
 * @param name the package name
 * @param man the {@code Manifest} containing package version and sealing
 * information
 * @param url the code source url for the package, or null if none
 * @throws IllegalArgumentException if the package name is
 * already defined by this class loader
 * @return the newly defined {@code Package} object
 *
 * @revised 9
 * @spec JPMS
 */
 protected Package definePackage(String name, Manifest man, URL url) {
 String specTitle = null, specVersion = null, specVendor = null;
 String implTitle = null, implVersion = null, implVendor = null;
 String sealed = null;
 URL sealBase = null;

 Attributes attr = SharedSecrets.javaUtilJarAccess()
 .getTrustedAttributes(man, name.replace('.', '/').concat("/"));
 if (attr != null) {
 specTitle = attr.getValue(Name.SPECIFICATION_TITLE);
 specVersion = attr.getValue(Name.SPECIFICATION_VERSION);
 specVendor = attr.getValue(Name.SPECIFICATION_VENDOR);
 implTitle = attr.getValue(Name.IMPLEMENTATION_TITLE);
 implVersion = attr.getValue(Name.IMPLEMENTATION_VERSION);
 implVendor = attr.getValue(Name.IMPLEMENTATION_VENDOR);
 sealed = attr.getValue(Name.SEALED);
 }
 attr = man.getMainAttributes();
 if (attr != null) {
 if (specTitle == null) {
 specTitle = attr.getValue(Name.SPECIFICATION_TITLE);
 }
 if (specVersion == null) {
 specVersion = attr.getValue(Name.SPECIFICATION_VERSION);
 }
 if (specVendor == null) {
 specVendor = attr.getValue(Name.SPECIFICATION_VENDOR);
 }
 if (implTitle == null) {
 implTitle = attr.getValue(Name.IMPLEMENTATION_TITLE);
 }
 if (implVersion == null) {
 implVersion = attr.getValue(Name.IMPLEMENTATION_VERSION);
 }
 if (implVendor == null) {
 implVendor = attr.getValue(Name.IMPLEMENTATION_VENDOR);
 }
 if (sealed == null) {
 sealed = attr.getValue(Name.SEALED);
 }
 }
 if ("true".equalsIgnoreCase(sealed)) {
 sealBase = url;
 }
 return definePackage(name, specTitle, specVersion, specVendor,
 implTitle, implVersion, implVendor, sealBase);
 }

 /*
 * Returns true if the specified package name is sealed according to the
 * given manifest.
 *
 * @throws SecurityException if the package name is untrusted in the manifest
 */
 private boolean isSealed(String name, Manifest man) {
 Attributes attr = SharedSecrets.javaUtilJarAccess()
 .getTrustedAttributes(man, name.replace('.', '/').concat("/"));
 String sealed = null;
 if (attr != null) {
 sealed = attr.getValue(Name.SEALED);
 }
 if (sealed == null) {
 if ((attr = man.getMainAttributes()) != null) {
 sealed = attr.getValue(Name.SEALED);
 }
 }
 return "true".equalsIgnoreCase(sealed);
 }

 /**
 * Finds the resource with the specified name on the URL search path.
 *
 * @param name the name of the resource
 * @return a {@code URL} for the resource, or {@code null}
 * if the resource could not be found, or if the loader is closed.
 */
 public URL findResource(final String name) {
 /*
 * The same restriction to finding classes applies to resources
 */
 URL url = AccessController.doPrivileged(
 new PrivilegedAction<>() {
 public URL run() {
 return ucp.findResource(name, true);
 }
 }, acc);

 return url != null ? URLClassPath.checkURL(url) : null;
 }

 /**
 * Returns an Enumeration of URLs representing all of the resources
 * on the URL search path having the specified name.
 *
 * @param name the resource name
 * @exception IOException if an I/O exception occurs
 * @return An {@code Enumeration} of {@code URL}s.
 * If the loader is closed, the Enumeration contains no elements.
 */
 public Enumeration<URL> findResources(final String name)
 throws IOException
 {
 final Enumeration<URL> e = ucp.findResources(name, true);

 return new Enumeration<>() {
 private URL url = null;

 private boolean next() {
 if (url != null) {
 return true;
 }
 do {
 URL u = AccessController.doPrivileged(
 new PrivilegedAction<>() {
 public URL run() {
 if (!e.hasMoreElements())
 return null;
 return e.nextElement();
 }
 }, acc);
 if (u == null)
 break;
 url = URLClassPath.checkURL(u);
 } while (url == null);
 return url != null;
 }

 public URL nextElement() {
 if (!next()) {
 throw new NoSuchElementException();
 }
 URL u = url;
 url = null;
 return u;
 }

 public boolean hasMoreElements() {
 return next();
 }
 };
 }

 /**
 * Returns the permissions for the given codesource object.
 * The implementation of this method first calls super.getPermissions
 * and then adds permissions based on the URL of the codesource.
 * <p>
 * If the protocol of this URL is "jar", then the permission granted
 * is based on the permission that is required by the URL of the Jar
 * file.
 * <p>
 * If the protocol is "file" and there is an authority component, then
 * permission to connect to and accept connections from that authority
 * may be granted. If the protocol is "file"
 * and the path specifies a file, then permission to read that
 * file is granted. If protocol is "file" and the path is
 * a directory, permission is granted to read all files
 * and (recursively) all files and subdirectories contained in
 * that directory.
 * <p>
 * If the protocol is not "file", then permission
 * to connect to and accept connections from the URL's host is granted.
 * @param codesource the codesource
 * @exception NullPointerException if {@code codesource} is {@code null}.
 * @return the permissions granted to the codesource
 */
 protected PermissionCollection getPermissions(CodeSource codesource)
 {
 PermissionCollection perms = super.getPermissions(codesource);

 URL url = codesource.getLocation();

 Permission p;
 URLConnection urlConnection;

 try {
 urlConnection = url.openConnection();
 p = urlConnection.getPermission();
 } catch (java.io.IOException ioe) {
 p = null;
 urlConnection = null;
 }

 if (p instanceof FilePermission) {
 // if the permission has a separator char on the end,
 // it means the codebase is a directory, and we need
 // to add an additional permission to read recursively
 String path = p.getName();
 if (path.endsWith(File.separator)) {
 path += "-";
 p = new FilePermission(path, SecurityConstants.FILE_READ_ACTION);
 }
 } else if ((p == null) && (url.getProtocol().equals("file"))) {
 String path = url.getFile().replace('/', File.separatorChar);
 path = ParseUtil.decode(path);
 if (path.endsWith(File.separator))
 path += "-";
 p = new FilePermission(path, SecurityConstants.FILE_READ_ACTION);
 } else {
 /**
 * Not loading from a 'file:' URL so we want to give the class
 * permission to connect to and accept from the remote host
 * after we've made sure the host is the correct one and is valid.
 */
 URL locUrl = url;
 if (urlConnection instanceof JarURLConnection) {
 locUrl = ((JarURLConnection)urlConnection).getJarFileURL();
 }
 String host = locUrl.getHost();
 if (host != null && !host.isEmpty())
 p = new SocketPermission(host,
 SecurityConstants.SOCKET_CONNECT_ACCEPT_ACTION);
 }

 // make sure the person that created this class loader
 // would have this permission

 if (p != null) {
 final SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 final Permission fp = p;
 AccessController.doPrivileged(new PrivilegedAction<>() {
 public Void run() throws SecurityException {
 sm.checkPermission(fp);
 return null;
 }
 }, acc);
 }
 perms.add(p);
 }
 return perms;
 }

 /**
 * Creates a new instance of URLClassLoader for the specified
 * URLs and parent class loader. If a security manager is
 * installed, the {@code loadClass} method of the URLClassLoader
 * returned by this method will invoke the
 * {@code SecurityManager.checkPackageAccess} method before
 * loading the class.
 *
 * @param urls the URLs to search for classes and resources
 * @param parent the parent class loader for delegation
 * @exception NullPointerException if {@code urls} or any of its
 * elements is {@code null}.
 * @return the resulting class loader
 */
 public static URLClassLoader newInstance(final URL[] urls,
 final ClassLoader parent) {
 // Save the caller's context
 final AccessControlContext acc = AccessController.getContext();
 // Need a privileged block to create the class loader
 URLClassLoader ucl = AccessController.doPrivileged(
 new PrivilegedAction<>() {
 public URLClassLoader run() {
 return new FactoryURLClassLoader(null, urls, parent, acc);
 }
 });
 return ucl;
 }

 /**
 * Creates a new instance of URLClassLoader for the specified
 * URLs and default parent class loader. If a security manager is
 * installed, the {@code loadClass} method of the URLClassLoader
 * returned by this method will invoke the
 * {@code SecurityManager.checkPackageAccess} before
 * loading the class.
 *
 * @param urls the URLs to search for classes and resources
 * @exception NullPointerException if {@code urls} or any of its
 * elements is {@code null}.
 * @return the resulting class loader
 */
 public static URLClassLoader newInstance(final URL[] urls) {
 // Save the caller's context
 final AccessControlContext acc = AccessController.getContext();
 // Need a privileged block to create the class loader
 URLClassLoader ucl = AccessController.doPrivileged(
 new PrivilegedAction<>() {
 public URLClassLoader run() {
 return new FactoryURLClassLoader(urls, acc);
 }
 });
 return ucl;
 }

 static {
 SharedSecrets.setJavaNetURLClassLoaderAccess(
 new JavaNetURLClassLoaderAccess() {
 @Override
 public AccessControlContext getAccessControlContext(URLClassLoader u) {
 return u.acc;
 }
 }
 );
 ClassLoader.registerAsParallelCapable();
 }
}

final class FactoryURLClassLoader extends URLClassLoader {

 static {
 ClassLoader.registerAsParallelCapable();
 }

 FactoryURLClassLoader(String name, URL[] urls, ClassLoader parent,
 AccessControlContext acc) {
 super(name, urls, parent, acc);
 }

 FactoryURLClassLoader(URL[] urls, AccessControlContext acc) {
 super(urls, acc);
 }

 public final Class<?> loadClass(String name, boolean resolve)
 throws ClassNotFoundException
 {
 // First check if we have permission to access the package. This
 // should go away once we've added support for exported packages.
 SecurityManager sm = System.getSecurityManager();
 if (sm != null) {
 int i = name.lastIndexOf('.');
 if (i != -1) {
 sm.checkPackageAccess(name.substring(0, i));
 }
 }
 return super.loadClass(name, resolve);
 }
}