src/java/org/apache/commons/vfs/provider/AbstractLayeredFileProvider.java

/*
 * Copyright 2002-2005 The Apache Software Foundation.
 * 
 * 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
 * 
 *      http://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.apache.commons.vfs.provider;

import org.apache.commons.vfs.FileName;
import org.apache.commons.vfs.FileObject;
import org.apache.commons.vfs.FileSystem;
import org.apache.commons.vfs.FileSystemException;
import org.apache.commons.vfs.FileSystemOptions;

/**
 * A {@link FileProvider} that is layered on top of another, such as the
 * contents of a zip or tar file.
 *
 * @author <a href="mailto:adammurdoch@apache.org">Adam Murdoch</a>
 * @version $Revision$ $Date$
 */
public abstract class AbstractLayeredFileProvider
    extends AbstractFileProvider
    implements FileProvider
{
    public AbstractLayeredFileProvider()
    {
        super();
        setFileNameParser(LayeredFileNameParser.getInstance());
    }

    /**
     * Locates a file object, by absolute URI.
     */
    public FileObject findFile(final FileObject baseFile,
                               final String uri,
                               final FileSystemOptions properties) throws FileSystemException
    {
        // Split the URI up into its parts
        final LayeredFileName name = (LayeredFileName) parseUri(baseFile!=null?baseFile.getName():null, uri);

        // Make the URI canonical

        // Resolve the outer file name
        final FileName fileName = name.getOuterName();
        final FileObject file = getContext().resolveFile(baseFile, fileName.getURI(), properties);

        // Create the file system
        final FileObject rootFile = createFileSystem(name.getScheme(), file, properties);

        // Resolve the file
        return rootFile.resolveFile(name.getPath());
    }

    /**
     * Creates a layered file system.
     */
    public synchronized FileObject createFileSystem(final String scheme,
                                                    final FileObject file,
                                                    final FileSystemOptions fileSystemOptions)
        throws FileSystemException
    {
        // Check if cached
        final FileName rootName = file.getName();
        FileSystem fs = findFileSystem(rootName, null);
        if (fs == null)
        {
            // Create the file system
            fs = doCreateFileSystem(scheme, file, fileSystemOptions);
            addFileSystem(rootName, fs);
        }
        return fs.getRoot();
    }

    /**
     * Creates a layered file system.  This method is called if the file system
     * is not cached.  The file system may implement {@link VfsComponent}.
     *
     * @param scheme The URI scheme.
     * @param file   The file to create the file system on top of.
     * @return The file system.
     */
    protected abstract FileSystem doCreateFileSystem(final String scheme,
                                                     final FileObject file,
                                                     final FileSystemOptions fileSystemOptions)
        throws FileSystemException;

}