Decompressing a string using Java.util.zip.Inflate

问题:

I'm trying to decode a string that I receive. It's compressed using the deflater here: https://github.com/dankogai/js-deflate And then base64 encoded.

However when I use the java inflater I get the following error message: unknown compression method.

    import sun.misc.BASE64Decoder;

    public void org() throws Exception{
    BASE64Decoder decoder = new BASE64Decoder();

    try {      

         String inputString = "84VWAVDY";
         byte[] decodedByteArray = decoder.decodeBuffer(inputString);

         // Decompress the bytes
         Inflater decompresser = new Inflater();
         decompresser.setInput(decodedByteArray);
         byte[] result = new byte[100];

         int resultLength = decompresser.inflate(result);
         decompresser.end();

         // Decode the bytes into a String
         String outputString = new String(result, 0, resultLength);
         System.out.println("OUTPUT:" + outputString);

    } catch (Exception e){
        System.out.println("Exception: " + e);
    }
}

This code is basically a copy/paste from the Java API. I have also tried to use the new Inflater(true); I.e the nowrap

"Note: When using the 'nowrap' option it is also necessary to provide an extra "dummy" byte as input. This is required by the ZLIB native library in order to support certain optimizations."

So where is this dummy byte supposed to be added? At the beginning or end of the "byte[] decodedByteArray" ?

So any ideas how to solve this problem? Do I only have to add the dummy byte, do I need to use some other methodes etc?

Well, that's it I guess, all help is appreciated!

Regards

John

回答1:

The dummy byte would be added at the end. However it is only needed for zlib 1.1.4 and earlier. The current versions of zlib don't need it. I'm not sure what version of zlib is used by java.util.zip.

回答2:

The base64 decode of "84VWAVDY" (f3 85 56 01 50 d8) is not a valid raw deflate stream, nor a valid wrapped (zlib nor gzip) deflate stream. So no matter what, you will get no satisfaction trying to inflate that data.