Java tutorial
/* * 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.compress.compressors.xz; import java.util.HashMap; import java.util.Map; import org.apache.commons.compress.compressors.FileNameUtil; /** * Utility code for the xz compression format. * @ThreadSafe * @since 1.4 */ public class XZUtils { private static final FileNameUtil fileNameUtil; /** * XZ Header Magic Bytes begin a XZ file. * * <p>This is a copy of {@code org.tukaani.xz.XZ.HEADER_MAGIC} in * XZ for Java version 1.5.</p> */ private static final byte[] HEADER_MAGIC = { (byte) 0xFD, '7', 'z', 'X', 'Z', '\0' }; static enum CachedAvailability { DONT_CACHE, CACHED_AVAILABLE, CACHED_UNAVAILABLE } private static volatile CachedAvailability cachedXZAvailability; static { final Map<String, String> uncompressSuffix = new HashMap<>(); uncompressSuffix.put(".txz", ".tar"); uncompressSuffix.put(".xz", ""); uncompressSuffix.put("-xz", ""); fileNameUtil = new FileNameUtil(uncompressSuffix, ".xz"); cachedXZAvailability = CachedAvailability.DONT_CACHE; try { Class.forName("org.osgi.framework.BundleEvent"); } catch (final Exception ex) { setCacheXZAvailablity(true); } } /** Private constructor to prevent instantiation of this utility class. */ private XZUtils() { } /** * Checks if the signature matches what is expected for a .xz file. * * <p>This is more or less a copy of the version found in {@link * XZCompressorInputStream} but doesn't depend on the presence of * XZ for Java.</p> * * @param signature the bytes to check * @param length the number of bytes to check * @return true if signature matches the .xz magic bytes, false otherwise * @since 1.9 */ public static boolean matches(final byte[] signature, final int length) { if (length < HEADER_MAGIC.length) { return false; } for (int i = 0; i < HEADER_MAGIC.length; ++i) { if (signature[i] != HEADER_MAGIC[i]) { return false; } } return true; } /** * Are the classes required to support XZ compression available? * @since 1.5 * @return true if the classes required to support XZ compression are available */ public static boolean isXZCompressionAvailable() { final CachedAvailability cachedResult = cachedXZAvailability; if (cachedResult != CachedAvailability.DONT_CACHE) { return cachedResult == CachedAvailability.CACHED_AVAILABLE; } return internalIsXZCompressionAvailable(); } private static boolean internalIsXZCompressionAvailable() { try { XZCompressorInputStream.matches(null, 0); return true; } catch (final NoClassDefFoundError error) { return false; } } /** * Detects common xz suffixes in the given filename. * * @param filename name of a file * @return {@code true} if the filename has a common xz suffix, * {@code false} otherwise */ public static boolean isCompressedFilename(final String filename) { return fileNameUtil.isCompressedFilename(filename); } /** * Maps the given name of a xz-compressed file to the name that the * file should have after uncompression. Commonly used file type specific * suffixes like ".txz" are automatically detected and * correctly mapped. For example the name "package.txz" is mapped to * "package.tar". And any filenames with the generic ".xz" suffix * (or any other generic xz suffix) is mapped to a name without that * suffix. If no xz suffix is detected, then the filename is returned * unmapped. * * @param filename name of a file * @return name of the corresponding uncompressed file */ public static String getUncompressedFilename(final String filename) { return fileNameUtil.getUncompressedFilename(filename); } /** * Maps the given filename to the name that the file should have after * compression with xz. Common file types with custom suffixes for * compressed versions are automatically detected and correctly mapped. * For example the name "package.tar" is mapped to "package.txz". If no * custom mapping is applicable, then the default ".xz" suffix is appended * to the filename. * * @param filename name of a file * @return name of the corresponding compressed file */ public static String getCompressedFilename(final String filename) { return fileNameUtil.getCompressedFilename(filename); } /** * Whether to cache the result of the XZ for Java check. * * <p>This defaults to {@code false} in an OSGi environment and {@code true} otherwise.</p> * @param doCache whether to cache the result * @since 1.9 */ public static void setCacheXZAvailablity(final boolean doCache) { if (!doCache) { cachedXZAvailability = CachedAvailability.DONT_CACHE; } else if (cachedXZAvailability == CachedAvailability.DONT_CACHE) { final boolean hasXz = internalIsXZCompressionAvailable(); cachedXZAvailability = hasXz ? CachedAvailability.CACHED_AVAILABLE : CachedAvailability.CACHED_UNAVAILABLE; } } // only exists to support unit tests static CachedAvailability getCachedXZAvailability() { return cachedXZAvailability; } }