urlclassloader.java

gcc的组建

  private void addURLs(URL[] newUrls)
  {
    for (int i = 0; i < newUrls.length; i++)
      {
	urls.add(newUrls[i]);
	addURLImpl(newUrls[i]);
      }
  }

  /**
   * Look in both Attributes for a given value.  The first Attributes
   * object, if not null, has precedence.
   */
  private String getAttributeValue(Attributes.Name name, Attributes first,
				   Attributes second)
  {
    String result = null;
    if (first != null)
      result = first.getValue(name);
    if (result == null)
      result = second.getValue(name);
    return result;
  }

  /**
   * Defines a Package based on the given name and the supplied manifest
   * information. The manifest indicates the title, version and
   * vendor information of the specification and implementation and whether the
   * package is sealed. If the Manifest indicates that the package is sealed
   * then the Package will be sealed with respect to the supplied URL.
   *
   * @param name The name of the package
   * @param manifest The manifest describing the specification,
   * implementation and sealing details of the package
   * @param url the code source url to seal the package
   * @return the defined Package
   * @throws IllegalArgumentException If this package name already exists
   * in this class loader
   */
  protected Package definePackage(String name, Manifest manifest, URL url)
    throws IllegalArgumentException
  {
    // Compute the name of the package as it may appear in the
    // Manifest.
    StringBuffer xform = new StringBuffer(name);
    for (int i = xform.length () - 1; i >= 0; --i)
      if (xform.charAt(i) == '.')
	xform.setCharAt(i, '/');
    xform.append('/');
    String xformName = xform.toString();

    Attributes entryAttr = manifest.getAttributes(xformName);
    Attributes attr = manifest.getMainAttributes();

    String specTitle
      = getAttributeValue(Attributes.Name.SPECIFICATION_TITLE,
			  entryAttr, attr);
    String specVersion
      = getAttributeValue(Attributes.Name.SPECIFICATION_VERSION,
			  entryAttr, attr);
    String specVendor
      = getAttributeValue(Attributes.Name.SPECIFICATION_VENDOR,
			  entryAttr, attr);
    String implTitle
      = getAttributeValue(Attributes.Name.IMPLEMENTATION_TITLE,
			  entryAttr, attr);
    String implVersion
      = getAttributeValue(Attributes.Name.IMPLEMENTATION_VERSION,
			  entryAttr, attr);
    String implVendor
      = getAttributeValue(Attributes.Name.IMPLEMENTATION_VENDOR,
			  entryAttr, attr);

    // Look if the Manifest indicates that this package is sealed
    // XXX - most likely not completely correct!
    // Shouldn't we also check the sealed attribute of the complete jar?
    // http://java.sun.com/products/jdk/1.4/docs/guide/extensions/spec.html#bundled
    // But how do we get that jar manifest here?
    String sealed = attr.getValue(Attributes.Name.SEALED);
    if ("false".equals(sealed))
      // make sure that the URL is null so the package is not sealed
      url = null;

    return definePackage(name,
			 specTitle, specVendor, specVersion,
			 implTitle, implVendor, implVersion,
			 url);
  }

  /**
   * Finds (the first) class by name from one of the locations. The locations
   * are searched in the order they were added to the URLClassLoader.
   *
   * @param className the classname to find
   * @exception ClassNotFoundException when the class could not be found or
   * loaded
   * @return a Class object representing the found class
   */
  protected Class findClass(final String className)
    throws ClassNotFoundException
  {
    // Just try to find the resource by the (almost) same name
    String resourceName = className.replace('.', '/') + ".class";
    int max = urlinfos.size();
    Resource resource = null;
    for (int i = 0; i < max && resource == null; i++)
      {
	URLLoader loader = (URLLoader)urlinfos.elementAt(i);
	if (loader == null)
	  continue;

	Class k = loader.getClass(className);
	if (k != null)
	  return k;

	resource = loader.getResource(resourceName);
      }
    if (resource == null)
      throw new ClassNotFoundException(className + " not found in " + this);

    // Try to read the class data, create the CodeSource, Package and
    // construct the class (and watch out for those nasty IOExceptions)
    try
      {
	byte[] data;
	InputStream in = resource.getInputStream();
	try
	  {
	    int length = resource.getLength();
	    if (length != -1)
	      {
		// We know the length of the data.
		// Just try to read it in all at once
		data = new byte[length];
		int pos = 0;
		while (length - pos > 0)
		  {
		    int len = in.read(data, pos, length - pos);
		    if (len == -1)
		      throw new EOFException("Not enough data reading from: "
					     + in);
		    pos += len;
		  }
	      }
	    else
	      {
		// We don't know the data length.
		// Have to read it in chunks.
		ByteArrayOutputStream out = new ByteArrayOutputStream(4096);
		byte[] b = new byte[4096];
		int l = 0;
		while (l != -1)
		  {
		    l = in.read(b);
		    if (l != -1)
		      out.write(b, 0, l);
		  }
		data = out.toByteArray();
	      }
	  }
	finally
	  {
	    in.close();
	  }
	final byte[] classData = data;

        // Now get the CodeSource
        final CodeSource source = resource.getCodeSource();

        // Find out package name
        String packageName = null;
        int lastDot = className.lastIndexOf('.');
        if (lastDot != -1)
          packageName = className.substring(0, lastDot);

        if (packageName != null && getPackage(packageName) == null)
          {
            // define the package
            Manifest manifest = resource.loader.getManifest();
            if (manifest == null)
              definePackage(packageName, null, null, null, null, null, null,
                            null);
            else
              definePackage(packageName, manifest, resource.loader.baseURL);
          }

        // And finally construct the class!
        SecurityManager sm = System.getSecurityManager();
        Class result = null;
        if (sm != null && securityContext != null)
          {
            result = (Class)AccessController.doPrivileged
              (new PrivilegedAction()
                {
                  public Object run()
                  {
                    return defineClass(className, classData,
                                       0, classData.length,
                                       source);
                  }
                }, securityContext);
          }
        else
          result = defineClass(className, classData, 0, classData.length, source);

        // Avoid NullPointerExceptions.
        Certificate[] resourceCertificates = resource.getCertificates();
        if(resourceCertificates != null)
          super.setSigners(result, resourceCertificates);
        
        return result;
      }
    catch (IOException ioe)
      {
	ClassNotFoundException cnfe;
	cnfe = new ClassNotFoundException(className + " not found in " + this);
	cnfe.initCause(ioe);
	throw cnfe;
      }
  }
  
  // Cached String representation of this URLClassLoader
  private String thisString;
  
  /**
   * Returns a String representation of this URLClassLoader giving the
   * actual Class name, the URLs that are searched and the parent
   * ClassLoader.
   */
  public String toString()
  {
    synchronized (this)
      {
	if (thisString == null)
	  {
	    StringBuffer sb = new StringBuffer();
	    sb.append(this.getClass().getName());
	    sb.append("{urls=[" );
	    URL[] thisURLs = getURLs();
	    for (int i = 0; i < thisURLs.length; i++)
	      {
		sb.append(thisURLs[i]);
		if (i < thisURLs.length - 1)
		  sb.append(',');
	      }
	    sb.append(']');
	    sb.append(", parent=");
	    sb.append(getParent());
	    sb.append('}');
	    thisString = sb.toString();
	  }
	return thisString;
      }
  }

  /**
   * Finds the first occurrence of a resource that can be found. The locations
   * are searched in the order they were added to the URLClassLoader.
   *
   * @param resourceName the resource name to look for
   * @return the URLResource for the resource if found, null otherwise
   */
  private Resource findURLResource(String resourceName)
  {
    int max = urlinfos.size();
    for (int i = 0; i < max; i++)
      {
        URLLoader loader = (URLLoader) urlinfos.elementAt(i);
        if (loader == null)
          continue;

        Resource resource = loader.getResource(resourceName);
        if (resource != null)
          return resource;
      }
    return null;
  }

  /**
   * Finds the first occurrence of a resource that can be found.
   *
   * @param resourceName the resource name to look for
   * @return the URL if found, null otherwise
   */
  public URL findResource(String resourceName)
  {
    Resource resource = findURLResource(resourceName);
    if (resource != null)
      return resource.getURL();

    // Resource not found
    return null;
  }

  /**
   * If the URLStreamHandlerFactory has been set this return the appropriate
   * URLStreamHandler for the given protocol, if not set returns null.
   *
   * @param protocol the protocol for which we need a URLStreamHandler
   * @return the appropriate URLStreamHandler or null
   */
  URLStreamHandler getURLStreamHandler(String protocol)
  {
    if (factory == null)
      return null;

    URLStreamHandler handler;
    synchronized (factoryCache)
      {
        // Check if there're handler for the same protocol in cache.
        HashMap cache = (HashMap) factoryCache.get(factory);
        handler = (URLStreamHandler) cache.get(protocol);
        if (handler == null)
          {
            // Add it to cache.
            handler = factory.createURLStreamHandler(protocol);
            cache.put(protocol, handler);
          }
      }
    return handler;
  }

  /**
   * Finds all the resources with a particular name from all the locations.
   *
   * @param resourceName the name of the resource to lookup
   * @return a (possible empty) enumeration of URLs where the resource can be
   * found
   * @exception IOException when an error occurs accessing one of the
   * locations
   */
  public Enumeration findResources(String resourceName)
    throws IOException
  {
    Vector resources = new Vector();
    int max = urlinfos.size();
    for (int i = 0; i < max; i++)
      {
        URLLoader loader = (URLLoader) urlinfos.elementAt(i);
        Resource resource = loader.getResource(resourceName);
        if (resource != null)
          resources.add(resource.getURL());
      }
    return resources.elements();
  }

  /**
   * Returns the permissions needed to access a particular code
   * source.  These permissions includes those returned by
   * <code>SecureClassLoader.getPermissions()</code> and the actual
   * permissions to access the objects referenced by the URL of the
   * code source.  The extra permissions added depend on the protocol
   * and file portion of the URL in the code source. If the URL has
   * the "file" protocol ends with a '/' character then it must be a
   * directory and a file Permission to read everything in that
   * directory and all subdirectories is added. If the URL had the
   * "file" protocol and doesn't end with a '/' character then it must
   * be a normal file and a file permission to read that file is
   * added. If the <code>URL</code> has any other protocol then a
   * socket permission to connect and accept connections from the host
   * portion of the URL is added.
   *
   * @param source The codesource that needs the permissions to be accessed
   * @return the collection of permissions needed to access the code resource
   * @see java.security.SecureClassLoader#getPermissions(CodeSource)
   */
  protected PermissionCollection getPermissions(CodeSource source)
  {
    // XXX - This implementation does exactly as the Javadoc describes.
    // But maybe we should/could use URLConnection.getPermissions()?
    // First get the permissions that would normally be granted
    PermissionCollection permissions = super.getPermissions(source);

    // Now add any extra permissions depending on the URL location.
    URL url = source.getLocation();
    String protocol = url.getProtocol();
    if (protocol.equals("file"))
      {
        String file = url.getFile();

        // If the file end in / it must be an directory.
        if (file.endsWith("/") || file.endsWith(File.separator))
          {
            // Grant permission to read everything in that directory and
            // all subdirectories.
            permissions.add(new FilePermission(file + "-", "read"));
          }
        else
          {
            // It is a 'normal' file.
            // Grant permission to access that file.
            permissions.add(new FilePermission(file, "read"));
          }
      }
    else
      {
        // Grant permission to connect to and accept connections from host
        String host = url.getHost();
        if (host != null)
          permissions.add(new SocketPermission(host, "connect,accept"));
      }

    return permissions;
  }

  /**
   * Returns all the locations that this class loader currently uses the
   * resolve classes and resource. This includes both the initially supplied
   * URLs as any URLs added later by the loader.
   * @return All the currently used URLs
   */
  public URL[] getURLs()
  {
    return (URL[]) urls.toArray(new URL[urls.size()]);
  }

  /**
   * Creates a new instance of a <code>URLClassLoader</code> that gets
   * classes from the supplied <code>URL</code>s. This class loader
   * will have as parent the standard system class loader.
   *
   * @param urls the initial URLs used to resolve classes and
   * resources
   *
   * @return the class loader
   *
   * @exception SecurityException when the calling code does not have
   * permission to access the given <code>URL</code>s
   */
  public static URLClassLoader newInstance(URL[] urls)
    throws SecurityException
  {
    return newInstance(urls, null);
  }

  /**
   * Creates a new instance of a <code>URLClassLoader</code> that gets
   * classes from the supplied <code>URL</code>s and with the supplied
   * loader as parent class loader.
   *
   * @param urls the initial URLs used to resolve classes and
   * resources
   * @param parent the parent class loader
   *
   * @return the class loader
   *
   * @exception SecurityException when the calling code does not have
   * permission to access the given <code>URL</code>s
   */
  public static URLClassLoader newInstance(URL[] urls, final ClassLoader parent)
    throws SecurityException
  {
    SecurityManager sm = System.getSecurityManager();
    if (sm == null)
      return new URLClassLoader(urls, parent);
    else
      {
        final Object securityContext = sm.getSecurityContext();

        // XXX - What to do with anything else then an AccessControlContext?
        if (! (securityContext instanceof AccessControlContext))
          throw new SecurityException("securityContext must be AccessControlContext: "
                                      + securityContext);

        URLClassLoader loader =
          (URLClassLoader) AccessController.doPrivileged(new PrivilegedAction()
              {
                public Object run()
                {
                  return new URLClassLoader(parent,
                                            (AccessControlContext) securityContext);
                }
              });
        loader.addURLs(urls);
        return loader;
      }
  }
}