Apple Developer Connection Student Program/ADC Tools Sampler CD Disk 3 1999.iso/Metrowerks CodeWarrior/Java Support/Java_Source/Java2/src/java/net/URLClassLoader.java

Java Source | 1999-05-28 | 17.7 KB | 522 lines | [TEXT/CWIE]

/*
 * @(#)URLClassLoader.java    1.61 98/09/24
 *
 * Copyright 1997, 1998 by Sun Microsystems, Inc.,
 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
 * All rights reserved.
 *
 * This software is the confidential and proprietary information
 * of Sun Microsystems, Inc. ("Confidential Information").  You
 * shall not disclose such Confidential Information and shall use
 * it only in accordance with the terms of the license agreement
 * you entered into with Sun.
 */

package java.net;

import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.io.File;
import java.io.FilePermission;
import java.io.InputStream;
import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandlerFactory;
import java.util.Enumeration;
import java.util.StringTokenizer;
import java.util.jar.Manifest;
import java.util.jar.Attributes;
import java.util.jar.Attributes.Name;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;
import java.security.AccessController;
import java.security.AccessControlContext;
import java.security.SecureClassLoader;
import java.security.CodeSource;
import java.security.Permission;
import java.security.PermissionCollection;
import sun.misc.Resource;
import sun.misc.URLClassPath;

/**
 * This class loader is used to load classes and resources from a search
 * path of URLs referring to both JAR files and directories. 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 opened as needed.
 * <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
 * @version 1.61, 09/24/98
 * @since   JDK1.2
 */
public class URLClassLoader extends SecureClassLoader {
    /* The search path for classes and resources */
    private URLClassPath ucp;

    /* The context to be used when loading classes and resources */
    private 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 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</code> 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</code> method doesn't allow
     *             creation of a class loader.
     * @see SecurityManager#checkCreateClassLoader
     */
    public URLClassLoader(URL[] urls, ClassLoader parent) {
    super(parent);
    // this is to make the stack depth consistent with 1.1
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
        security.checkCreateClassLoader();
    }
    ucp = new URLClassPath(urls);
    acc = AccessController.getContext();
    }

    /**
     * Constructs a new URLClassLoader for the specified URLs using the
     * default delegation parent <code>ClassLoader</code>. 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</code> 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</code> method doesn't allow
     *             creation of a class loader.
     * @see SecurityManager#checkCreateClassLoader
     */
    public URLClassLoader(URL[] urls) {
    super();
    // this is to make the stack depth consistent with 1.1
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
        security.checkCreateClassLoader();
    }
    ucp = new URLClassPath(urls);
    acc = AccessController.getContext();
    }

    /**
     * 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 URLs.
     *
     * <p>If there is a security manager, this method first
     * calls the security manager's <code>checkCreateClassLoader</code> 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</code> method doesn't allow
     *             creation of a class loader.
     * @see SecurityManager#checkCreateClassLoader
     */
    public URLClassLoader(URL[] urls, ClassLoader parent,
              URLStreamHandlerFactory factory) {
    super(parent);
    // this is to make the stack depth consistent with 1.1
    SecurityManager security = System.getSecurityManager();
    if (security != null) {
        security.checkCreateClassLoader();
    }
    ucp = new URLClassPath(urls, factory);
    acc = AccessController.getContext();
    }

    /**
     * Appends the specified URL to the list of URLs to search for
     * classes and resources.
     *
     * @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.
     */
    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
     */
    protected Class findClass(final String name)
     throws ClassNotFoundException
    {
    try {
        return (Class)
        AccessController.doPrivileged(new PrivilegedExceptionAction() {
            public Object 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 {
                throw new ClassNotFoundException(name);
            }
            }
        }, acc);
    } catch (java.security.PrivilegedActionException pae) {
        throw (ClassNotFoundException) pae.getException();
    }
    }

    /*
     * 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 {
    int i = name.lastIndexOf('.');
    URL url = res.getCodeSourceURL();
    if (i != -1) {
        String pkgname = name.substring(0, i);
        // Check if package already loaded.
        Package pkg = getPackage(pkgname);
        Manifest man = res.getManifest();
        if (pkg != null) {
        // Package found, so check package sealing.
        boolean ok;
        if (pkg.isSealed()) {
            // Verify that code source URL is the same.
            ok = pkg.isSealed(url);
        } else {
            // Make sure we are not attempting to seal the package
            // at this code source URL.
            ok = (man == null) || !isSealed(pkgname, man);
        }
        if (!ok) {
            throw new SecurityException("sealing violation");
        }
        } else {
        if (man != null) {
            definePackage(pkgname, man, url);
        }
        }
    }
    // Now read the class bytes and define the class
    byte[] b = res.getBytes();
    java.security.cert.Certificate[] certs = res.getCertificates();
    CodeSource cs = new CodeSource(url, certs);
    return defineClass(name, b, 0, b.length, cs);
    }

    /**
     * Defines a new package by name in this ClassLoader. The attributes
     * contained in the specified 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 Manifest containing package version and sealing
     *              information
     * @param url   the code source url for the package, or null if none
     * @exception   IllegalArgumentException if the package name duplicates
     *              an existing package either in this class loader or one
     *              of its ancestors
     */
    protected Package definePackage(String name, Manifest man, URL url)
    throws IllegalArgumentException
    {
    String path = name.replace('.', '/').concat("/");
    String specTitle = null, specVersion = null, specVendor = null;
    String implTitle = null, implVersion = null, implVendor = null;
    String sealed = null;
    URL sealBase = null;

    Attributes attr = man.getAttributes(path);
    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.
     */
    private boolean isSealed(String name, Manifest man) {
    String path = name.replace('.', '/').concat("/");
    Attributes attr = man.getAttributes(path);
    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.
     * Returns a URL for the resource, or null if the resource could not
     * be found.
     *
     * @param name the name of the resource
     */
    public URL findResource(String name) {
        Resource res = ucp.getResource(name, true);
        return res != null ? res.getURL() : 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
     */
    public Enumeration findResources(String name) throws IOException {
    final Enumeration e = ucp.getResources(name, true);

    return new Enumeration() {
        public Object nextElement() {
        return ((Resource)e.nextElement()).getURL();
        }
        public boolean hasMoreElements() {
        return e.hasMoreElements();
        }
    };
    }

    /**
     * Returns the permissions for the given codesource object.
     * The implementation of this method first calls super.getPermissions,
     * to get the permissions
     * granted by the policy, and then adds additional permissions
     * based on the URL of the codesource.
     * <p>
     * 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
     * to connect to and accept connections from the URL's host is granted.
     * @param codesource the codesource
     * @return the permissions granted to the codesource
     */
    protected PermissionCollection getPermissions(CodeSource codesource)
    {
    PermissionCollection perms = super.getPermissions(codesource);

    URL url = codesource.getLocation();

    Permission p;

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

        p = 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, "read");
        }
    } else if ((p == null) && (url.getProtocol().equals("file"))) {
        String path = url.getFile().replace('/', File.separatorChar);
        if (path.endsWith(File.separator))
        path += "-";
        p =  new FilePermission(path, "read");
    } else {
        String host = url.getHost();
        if (host == null)
        host = "localhost";
        p = new SocketPermission(host,"connect, accept");
    }

    // 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 Object 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</code> method of the URLClassLoader
     * returned by this method will invoke the
     * <code>SecurityManager.checkPackageAccess</code> method before
     * loading the class.
     *
     * @param urls the URLs to search for classes and resources
     * @param parent the parent class loader for delegation
     * @return the resulting class loader
     */
    public static URLClassLoader newInstance(final URL[] urls,
                         final ClassLoader parent) {
    // Save the caller's context
    AccessControlContext acc = AccessController.getContext();
    // Need a privileged block to create the class loader
    URLClassLoader ucl =
        (URLClassLoader) AccessController.doPrivileged(new PrivilegedAction() {
        public Object run() {
            return new FactoryURLClassLoader(urls, parent);
        }
        });
    // Now set the context on the loader using the one we saved,
    // not the one inside the privileged block...
    ucl.acc = 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</code> method of the URLClassLoader
     * returned by this method will invoke the
     * <code>SecurityManager.checkPackageAccess</code> before
     * loading the class.
     *
     * @param urls the URLs to search for classes and resources
     * @return the resulting class loader
     */
    public static URLClassLoader newInstance(final URL[] urls) {
    // Save the caller's context
    AccessControlContext acc = AccessController.getContext();
    // Need a privileged block to create the class loader
    URLClassLoader ucl = (URLClassLoader)
        AccessController.doPrivileged(new PrivilegedAction() {
        public Object run() {
            return new FactoryURLClassLoader(urls);
        }
        });

    // Now set the context on the loader using the one we saved,
    // not the one inside the privileged block...
    ucl.acc = acc;
    return ucl;
    }
}

final class FactoryURLClassLoader extends URLClassLoader {

    FactoryURLClassLoader(URL[] urls, ClassLoader parent) {
    super(urls, parent);
    }

    FactoryURLClassLoader(URL[] urls) {
    super(urls);
    }

    public final synchronized 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);
    }
}