How to GZip decompress a compressed String data with Java code

Question

I have some code to uncompress gzip a compressedString as below:

public static String decompress(String compressedString) throws IOException {
        byte[] byteCompressed = compressedString.getBytes(StandardCharsets.UTF_8)
        final StringBuilder outStr = new StringBuilder();
        if ((byteCompressed == null) || (byteCompressed.length == 0)) {
            return "";
        }
        if (isCompressed(byteCompressed)) {
            final GZIPInputStream gis = new GZIPInputStream(new ByteArrayInputStream(byteCompressed));
            final BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(gis, "UTF-8"));

            String line;
            while ((line = bufferedReader.readLine()) != null) {
                outStr.append(line);
            }
        } else {
            outStr.append(byteCompressed);
        }
        return outStr.toString();
    }

public static boolean isCompressed(final byte[] compressed) {
        return (compressed[0] == (byte) (GZIPInputStream.GZIP_MAGIC)) && (compressed[1] == (byte) (GZIPInputStream.GZIP_MAGIC >> 8));
    }

I use this code to uncompress a String as below: H4sIAAAAAAAAAHNJLQtJLS4BALwLiloHAAAA

But this code uncompress a unexpected String although I can uncompress online normally in the web

Anyone can help me give the right uncompress code? Thanks

Mark Rotteveel · Accepted Answer · 2021-10-28 08:56:44Z

4

Your string is base64 encoded gzip data, so you need to base64 decode it, instead of trying to encode it as UTF-8 bytes.

String input = "H4sIAAAAAAAAAHNJLQtJLS4BALwLiloHAAAA";
byte[] byteCompressed = Base64.getDecoder().decode(input);
// ... rest of your code

answered Oct 28, 2021 at 8:56

Mark Rotteveel

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