Utilities for working with GZIP archives.

GZIPUtils.java

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.util.LinkedList;
import java.util.List;
import java.util.zip.GZIPInputStream;

import org.apache.commons.compress.archivers.ArchiveException;
import org.apache.commons.compress.archivers.ArchiveStreamFactory;
import org.apache.commons.compress.archivers.tar.TarArchiveEntry;
import org.apache.commons.compress.archivers.tar.TarArchiveInputStream;
import org.apache.commons.compress.utils.IOUtils;

import travel.opas.core.util.Log;

/**
 * Utilities for working with GZIP archives.
 * 
 * @author e.shishkin
 * 
 */
public class GZIPUtils {
	private static final String LOG_TAG = GZIPUtils.class.getSimpleName();
	
	/**
	 * Invisible constructor.
	 */
	private GZIPUtils() {}

	/**
	 * Untar an input file into an output file.
	 * <p>
	 * The output file is created in the output folder, having the same name as
	 * the input file, minus the '.tar' extension.
	 * 
	 * @param inputFile the input .tar file
	 * @param outputDir the output directory file.
	 * @return The {@link List} of {@link File}s with the untared content.
	 * @throws IOException
	 * @throws FileNotFoundException
	 * @throws ArchiveException
	 */
	public static List<File> unTar(final File inputFile, final File outputDir)
			throws FileNotFoundException, IOException, ArchiveException {
		Log.v(LOG_TAG, "unTar() called: inputFile=[%s], outputDir=[%s]",
				inputFile.getAbsoluteFile(), outputDir.getAbsoluteFile());
		
		final List<File> untaredFiles = new LinkedList<File>();
		final TarArchiveInputStream in = 
				(TarArchiveInputStream) new ArchiveStreamFactory()
				.createArchiveInputStream("tar", new FileInputStream(inputFile));
		try {
			TarArchiveEntry entry = null;
			while ((entry = (TarArchiveEntry) in.getNextEntry()) != null) {
				final File outputFile = new File(outputDir, entry.getName());
				if (entry.isDirectory()) {
					Log.d(LOG_TAG, "Attempting to write output directory %s.",
							outputFile.getAbsolutePath());
					if (!outputFile.exists()) {
						Log.d(LOG_TAG, "Attempting to create output directory %s.",
								outputFile.getAbsolutePath());
						if (!outputFile.mkdirs()) {
							throw new IllegalStateException(String.format(
									"Couldn't create directory %s.",
									outputFile.getAbsolutePath()));
						}
					}
				} else {
					Log.d(LOG_TAG, "Creating output file %s.", outputFile.getAbsolutePath());
					final OutputStream out = new FileOutputStream(outputFile);
					try {
						IOUtils.copy(in, out);
					} finally {
						out.close();
					}
				}
				untaredFiles.add(outputFile);
			}
		} finally {
			in.close();
		}

		return untaredFiles;
	}

	/**
	 * Ungzip an input file into an output file.
	 * <p>
	 * The output file is created in the output folder, having the same name as
	 * the input file, minus the '.gz' extension.
	 * 
	 * @param inputFile the input .gz file
	 * @param outputDir the output directory file.
	 * @return The {@File} with the ungzipped content.
	 * @throws IOException
	 * @throws FileNotFoundException
	 */
	public static File unGzip(final File inputFile, final File outputDir)
			throws FileNotFoundException, IOException {
		Log.v(LOG_TAG, "unGzip() called: inputFile=[%s], outputDir=[%s]",
				inputFile.getAbsoluteFile(), outputDir.getAbsoluteFile());
		
		final File outputFile = new File(outputDir, inputFile.getName()
				.substring(0, inputFile.getName().length() - 3));

		final GZIPInputStream in = new GZIPInputStream(new FileInputStream(inputFile));
		final FileOutputStream out = new FileOutputStream(outputFile);
		
		// this is storage overwritten on each iteration with bytes
		int bufferSize = 1024 * 4; // 4 kB
		byte[] buffer = new byte[bufferSize];
		try {
			// we need to know how may bytes were read to write them to the output
			int len = 0;
			while ((len = in.read(buffer)) != -1) {
				out.write(buffer, 0, len);
			}
			out.flush();
		} finally {
			out.close();
			in.close();
		}

		return outputFile;
	}

}

Wrap InputStream to BufferInputStream and OutputStream to BufferOutputStream