Java : GZIPInputStream (ZIP) with Examples

// --------
// Compression
final var out = new ByteArrayOutputStream();
try (final var gos = new GZIPOutputStream(out)) {
    gos.write("aaaaa".getBytes());
    gos.write("ZZZZZ".getBytes());
}

final var compressed = out.toByteArray();

// [31, -117, 8, 0, 0, 0, 0, 0, 0, -1, 75, 76, 4,
//  -126, 40, 16, 0, 0, -86, 55, 77, 24, 10, 0, 0, 0]
System.out.println(Arrays.toString(compressed));

// --------
// Decompression
try (final var gis = new GZIPInputStream(new ByteArrayInputStream(compressed))) {
    final var uncompressed = gis.readAllBytes();

    // [97, 97, 97, 97, 97, 90, 90, 90, 90, 90]
    System.out.println(Arrays.toString(uncompressed));

    // aaaaaZZZZZ
    System.out.println(new String(uncompressed));
}

Helper method for code examples

Code examples on this page use the helper method below.

// Compress a string.
public byte[] deflate(String str) throws IOException {
    final var out = new ByteArrayOutputStream();
    try (final var gos = new GZIPOutputStream(out)) {
        gos.write(str.getBytes());
    }

    return out.toByteArray();
}

protected CRC32 crc

CRC-32 for uncompressed data.

protected. I think it's rare to create a subclass of this class. Therefore, the code example is omitted.

protected boolean eos

Indicates end of input stream.

protected. I think it's rare to create a subclass of this class. Therefore, the code example is omitted.

static final int GZIP_MAGIC

GZIP header magic number.

System.out.printf("%#x", GZIPInputStream.GZIP_MAGIC); // 0x8b1f

buf, inf, len

Please see the link below.

• Java API Examples : InflaterInputStream

in

Please see the link below.

• Java API Examples : FilterInputStream

GZIPInputStream (InputStream in)

Creates a new input stream with a default buffer size.

The deflate method is here.

final var bytes = deflate("aaaaa");

// [31, -117, 8, 0, 0, 0, 0, 0, 0, -1, 75, 76, 4, 2,
//  0, -71, -109, -84, -18, 5, 0, 0, 0]
System.out.println(Arrays.toString(bytes));

try (final var gis = new GZIPInputStream(new ByteArrayInputStream(bytes))) {
    final var uncompressed = gis.readAllBytes();

    // [97, 97, 97, 97, 97]
    System.out.println(Arrays.toString(uncompressed));

    // aaaaa
    System.out.println(new String(uncompressed));
}

GZIPInputStream (InputStream in, int size)

Creates a new input stream with the specified buffer size.

The deflate method is here.

Please see GZIPInputStream(InputStream in) for in parameter.

class MyInputStream extends GZIPInputStream {
    public MyInputStream(InputStream in) throws IOException {
        super(in);
    }

    public MyInputStream(InputStream in, int size) throws IOException {
        super(in, size);
    }

    int getSize() {
        return buf.length;
    }
}

final var bytes = deflate("");

// [31, -117, 8, 0, 0, 0, 0, 0, 0, -1, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0]
System.out.println(Arrays.toString(bytes));

try (final var is = new MyInputStream(new ByteArrayInputStream(bytes))) {
    System.out.println(is.getSize()); // 512
}

try (final var is = new MyInputStream(new ByteArrayInputStream(bytes), 1024)) {
    System.out.println(is.getSize()); // 1024
}

void close ()

Closes this input stream and releases any system resources associated with the stream.

The deflate method is here.

final var file = Path.of("R:", "java-work", "aaa.gz");
System.out.println(file); // R:\java-work\aaa.gz

final var bytes = deflate("aaaaa");

// [31, -117, 8, 0, 0, 0, 0, 0, 0, -1, 75, 76, 4, 2,
//  0, -71, -109, -84, -18, 5, 0, 0, 0]
System.out.println(Arrays.toString(bytes));
Files.write(file, bytes);

try (final var gis = new GZIPInputStream(Files.newInputStream(file))) {
    final var uncompressed = gis.readAllBytes();

    // [97, 97, 97, 97, 97]
    System.out.println(Arrays.toString(uncompressed));

    // aaaaa
    System.out.println(new String(uncompressed));
}

An example without try-with-resources.

final var file = Path.of("R:", "java-work", "aaa.gz");
System.out.println(file); // R:\java-work\aaa.gz

final var bytes = deflate("aaaaa");

// [31, -117, 8, 0, 0, 0, 0, 0, 0, -1, 75, 76, 4, 2,
//  0, -71, -109, -84, -18, 5, 0, 0, 0]
System.out.println(Arrays.toString(bytes));
Files.write(file, bytes);

final var gis = new GZIPInputStream(Files.newInputStream(file));
try {
    final var uncompressed = gis.readAllBytes();

    // [97, 97, 97, 97, 97]
    System.out.println(Arrays.toString(uncompressed));

    // aaaaa
    System.out.println(new String(uncompressed));
} finally {
    gis.close();
}

int read (byte[] buf, int off, int len)

Reads uncompressed data into an array of bytes.

The deflate method is here.

final var str = "abcdef";
System.out.println(Arrays.toString(str.getBytes())); // [97, 98, 99, 100, 101, 102]

final var bytes = deflate(str);

// [31, -117, 8, 0, 0, 0, 0, 0, 0, -1, 75, 76, 74, 78,
//  73, 77, 3, 0, -17, 57, -114, 75, 6, 0, 0, 0]
System.out.println(Arrays.toString(bytes));

try (final var gis = new GZIPInputStream(new ByteArrayInputStream(bytes))) {
    final var b1 = new byte[5];
    System.out.println(gis.read(b1, 0, 3)); // 3
    System.out.println(Arrays.toString(b1)); // [97, 98, 99, 0, 0]

    final var b2 = new byte[5];
    System.out.println(gis.read(b2, 1, 2)); // 2
    System.out.println(Arrays.toString(b2)); // [0, 100, 101, 0, 0]

    final var b3 = new byte[5];
    System.out.println(gis.read(b3, 0, 5)); // 1
    System.out.println(Arrays.toString(b3)); // [102, 0, 0, 0, 0]
}

available, fill, mark, markSupported, read, reset, skip

Please see the link below.

• Java API Examples : InflaterInputStream

read

Please see the link below.

• Java API Examples : FilterInputStream

nullInputStream, readAllBytes, readNBytes, readNBytes, skipNBytes, transferTo

Please see the link below.

• Java API Examples : InputStream