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Apache Commons VFS is a Virtual File System library.
There is a newer version: 2.9.0
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.vfs2.provider.jar;

import java.io.File;
import java.io.IOException;
import java.util.Collection;
import java.util.jar.Attributes;
import java.util.jar.Attributes.Name;
import java.util.jar.JarFile;
import java.util.jar.Manifest;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;

import org.apache.commons.vfs2.Capability;
import org.apache.commons.vfs2.FileObject;
import org.apache.commons.vfs2.FileSystemException;
import org.apache.commons.vfs2.FileSystemOptions;
import org.apache.commons.vfs2.provider.AbstractFileName;
import org.apache.commons.vfs2.provider.zip.ZipFileObject;
import org.apache.commons.vfs2.provider.zip.ZipFileSystem;

/**
 * A read-only file system for Jar files.
 */
public class JarFileSystem extends ZipFileSystem {
    private Attributes attributes;

    protected JarFileSystem(final AbstractFileName rootName, final FileObject file,
            final FileSystemOptions fileSystemOptions) throws FileSystemException {
        super(rootName, file, fileSystemOptions);
    }

    // @Override
    // protected FileObject createFile(AbstractFileName name) throws FileSystemException
    // {
    // return new JarFileObject(name, null, this, false);
    // }

    @Override
    protected ZipFile createZipFile(final File file) throws FileSystemException {
        try {
            return new JarFile(file);
        } catch (final IOException ioe) {
            throw new FileSystemException("vfs.provider.jar/open-jar-file.error", file, ioe);
        }
    }

    @Override
    protected ZipFileObject createZipFileObject(final AbstractFileName name, final ZipEntry entry)
            throws FileSystemException {
        return new JarFileObject(name, entry, this, true);
    }

    /**
     * Returns the capabilities of this file system.
     */
    @Override
    protected void addCapabilities(final Collection caps) {
        // super.addCapabilities(caps);
        caps.addAll(JarFileProvider.capabilities);
    }

    Attributes getAttributes() throws IOException {
        if (attributes == null) {
            final Manifest man = ((JarFile) getZipFile()).getManifest();
            if (man == null) {
                attributes = new Attributes(1);
            } else {
                attributes = man.getMainAttributes();
                if (attributes == null) {
                    attributes = new Attributes(1);
                }
            }
        }

        return attributes;
    }

    Object getAttribute(final Name attrName) throws FileSystemException {
        try {
            final Attributes attr = getAttributes();
            final String value = attr.getValue(attrName);
            return value;
        } catch (final IOException ioe) {
            throw new FileSystemException(attrName.toString(), ioe);
        }
    }

    Name lookupName(final String attrName) {
        if (Name.CLASS_PATH.toString().equals(attrName)) {
            return Name.CLASS_PATH;
        } else if (Name.CONTENT_TYPE.toString().equals(attrName)) {
            return Name.CONTENT_TYPE;
        } else if (Name.EXTENSION_INSTALLATION.toString().equals(attrName)) {
            return Name.EXTENSION_INSTALLATION;
        } else if (Name.EXTENSION_LIST.toString().equals(attrName)) {
            return Name.EXTENSION_LIST;
        } else if (Name.EXTENSION_NAME.toString().equals(attrName)) {
            return Name.EXTENSION_NAME;
        } else if (Name.IMPLEMENTATION_TITLE.toString().equals(attrName)) {
            return Name.IMPLEMENTATION_TITLE;
        } else if (Name.IMPLEMENTATION_URL.toString().equals(attrName)) {
            return Name.IMPLEMENTATION_URL;
        } else if (Name.IMPLEMENTATION_VENDOR.toString().equals(attrName)) {
            return Name.IMPLEMENTATION_VENDOR;
        } else if (Name.IMPLEMENTATION_VENDOR_ID.toString().equals(attrName)) {
            return Name.IMPLEMENTATION_VENDOR_ID;
        } else if (Name.IMPLEMENTATION_VERSION.toString().equals(attrName)) {
            return Name.IMPLEMENTATION_VENDOR;
        } else if (Name.MAIN_CLASS.toString().equals(attrName)) {
            return Name.MAIN_CLASS;
        } else if (Name.MANIFEST_VERSION.toString().equals(attrName)) {
            return Name.MANIFEST_VERSION;
        } else if (Name.SEALED.toString().equals(attrName)) {
            return Name.SEALED;
        } else if (Name.SIGNATURE_VERSION.toString().equals(attrName)) {
            return Name.SIGNATURE_VERSION;
        } else if (Name.SPECIFICATION_TITLE.toString().equals(attrName)) {
            return Name.SPECIFICATION_TITLE;
        } else if (Name.SPECIFICATION_VENDOR.toString().equals(attrName)) {
            return Name.SPECIFICATION_VENDOR;
        } else if (Name.SPECIFICATION_VERSION.toString().equals(attrName)) {
            return Name.SPECIFICATION_VERSION;
        } else {
            return new Name(attrName);
        }
    }

    /**
     * Retrives the attribute with the specified name. The default implementation simply throws an exception.
     *
     * @param attrName The attiribute's name.
     * @return The value of the attribute.
     * @throws FileSystemException if an error occurs.
     */
    @Override
    public Object getAttribute(final String attrName) throws FileSystemException {
        final Name name = lookupName(attrName);
        return getAttribute(name);
    }

    @Override
    protected ZipFile getZipFile() throws FileSystemException {
        // make accessible
        return super.getZipFile();
    }

}