Compression / Decompression of Strings using the deflater

Question

I want to compress/decompress and serialize/deserialize String content. I'm using the following two static functions.

/**
 * Compress data based on the {@link Deflater}.
 * 
 * @param pToCompress
 *            input byte-array
 * @return compressed byte-array
 * @throws NullPointerException
 *             if {@code pToCompress} is {@code null}
 */
public static byte[] compress(@Nonnull final byte[] pToCompress) {
    checkNotNull(pToCompress);

    // Compressed result.
    byte[] compressed = new byte[] {};

    // Create the compressor.
    final Deflater compressor = new Deflater();
    compressor.setLevel(Deflater.BEST_SPEED);

    // Give the compressor the data to compress.
    compressor.setInput(pToCompress);
    compressor.finish();

    /*
     * Create an expandable byte array to hold the compressed data.
     * You cannot use an array that's the same size as the orginal because
     * there is no guarantee that the compressed data will be smaller than
     * the uncompressed data.
     */
    try (ByteArrayOutputStream bos = new ByteArrayOutputStream(pToCompress.length)) {
        // Compress the data.
        final byte[] buf = new byte[1024];
        while (!compressor.finished()) {
            final int count = compressor.deflate(buf);
            bos.write(buf, 0, count);
        }

        // Get the compressed data.
        compressed = bos.toByteArray();
    } catch (final IOException e) {
        LOGWRAPPER.error(e.getMessage(), e);
        throw new RuntimeException(e);
    }


    return compressed;
}

/**
 * Decompress data based on the {@link Inflater}.
 * 
 * @param pCompressed
 *            input string
 * @return compressed byte-array
 * @throws NullPointerException
 *             if {@code pCompressed} is {@code null}
 */
public static byte[] decompress(@Nonnull final byte[] pCompressed) {
    checkNotNull(pCompressed);

    // Create the decompressor and give it the data to compress.
    final Inflater decompressor = new Inflater();
    decompressor.setInput(pCompressed);

    byte[] decompressed = new byte[] {};

    // Create an expandable byte array to hold the decompressed data.
    try (final ByteArrayOutputStream bos = new ByteArrayOutputStream(pCompressed.length)) {
        // Decompress the data.
        final byte[] buf = new byte[1024];
        while (!decompressor.finished()) {
            try {
                final int count = decompressor.inflate(buf);
                bos.write(buf, 0, count);
            } catch (final DataFormatException e) {
                LOGWRAPPER.error(e.getMessage(), e);
                throw new RuntimeException(e);
            }
        }
        // Get the decompressed data.
        decompressed = bos.toByteArray();
    } catch (final IOException e) {
        LOGWRAPPER.error(e.getMessage(), e);
    }

    return decompressed;
}

Yet, compared to non-compressed values it's orders of magnitudes slower even if I'm caching the decompressed-result and the values are only decompressed if the content is really needed.

That is, it's used for a DOM-like persistable tree-structure and XPath-queries which force the decompression of the String-values are about 50 times if not even more slower (not really benchmarked, just executed unit tests). My laptop even freezes after some unit tests (everytime, checked it about 5-times), because Eclipse isn't responding anymore due to heavy disk I/O and what not. I've even set the compression level to Deflater.BEST_SPEED, whereas other compression levels might be better, maybe I'm providing a configuration option parameter which can be set for resources. Maybe I've messed something up as I haven't used the deflater before. I'm even only compressing content where the String lenght is > 10.

Edit: After considering to extract the Deflater instantiation to a static field it seems creating an instance of deflater and inflater is very costly as the performance bottleneck is gone and perhaps without microbenchmarks or the like I can't see any performance loss :-) I'm just resetting the deflater/inflater before using a new input.

How are you measuring the performance of your compression and decompression algorithms? Could you please share your idea/code regarding this? Are you calculating compression ratio and compression time of your algorithm? if so, could you please share the experience with me? I have implemented compression and decompression algorithm for random strings and now I am in need of measuring the performance of my algorithms by calculating compression ratio, compression time etc. Any kind of help will be appreciated. Thanks! — K M Rakibul Islam

tom tom · Accepted Answer · 2012-03-03T08:02:38

How you considered using the higher level api like Gzip.

Here is an example for compressing:

public static byte[] compressToByte(final String data, final String encoding)
    throws IOException
{
    if (data == null || data.length == 0)
    {
        return null;
    }
    else
    {
        byte[] bytes = data.getBytes(encoding);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        GZIPOutputStream os = new GZIPOutputStream(baos);
        os.write(bytes, 0, bytes.length);
        os.close();
        byte[] result = baos.toByteArray();
        return result;
    }
}

Here is an example for uncompressing:

public static String unCompressString(final byte[] data, final String encoding)
    throws IOException
{
    if (data == null || data.length == 0)
    {
        return null;
    }
    else
    {
        ByteArrayInputStream bais = new ByteArrayInputStream(data);
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();
        GZIPInputStream is = new GZIPInputStream(bais);
        byte[] tmp = new byte[256];
        while (true)
        {
            int r = is.read(tmp);
            if (r < 0)
            {
                break;
            }
            buffer.write(tmp, 0, r);
        }
        is.close();

        byte[] content = buffer.toByteArray();
        return new String(content, 0, content.length, encoding);
    }
}

We get very good performance and compression ratio with this.

The zip api is also an option.

Compression / Decompression of Strings using the deflater

2 Answers