Is there any way to check if InputStream has been gzipped? Here's the code:
public static InputStream decompressStream(InputStream input) {
try {
GZIPInputStream gs = new GZIPInputStream(input);
return gs;
} catch (IOException e) {
logger.info("Input stream not in the GZIP format, using standard format");
return input;
}
}
I tried this way but it doesn't work as expected - values read from the stream are invalid. EDIT: Added the method I use to compress data:
public static byte[] compress(byte[] content) {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
try {
GZIPOutputStream gs = new GZIPOutputStream(baos);
gs.write(content);
gs.close();
} catch (IOException e) {
logger.error("Fatal error occured while compressing data");
throw new RuntimeException(e);
}
double ratio = (1.0f * content.length / baos.size());
if (ratio > 1) {
logger.info("Compression ratio equals " + ratio);
return baos.toByteArray();
}
logger.info("Compression not needed");
return content;
}
It's not foolproof but it's probably the easiest and doesn't rely on any external data. Like all decent formats, GZip too begins with a magic number which can be quickly checked without reading the entire stream.
public static InputStream decompressStream(InputStream input) {
PushbackInputStream pb = new PushbackInputStream( input, 2 ); //we need a pushbackstream to look ahead
byte [] signature = new byte[2];
int len = pb.read( signature ); //read the signature
pb.unread( signature, 0, len ); //push back the signature to the stream
if( signature[ 0 ] == (byte) 0x1f && signature[ 1 ] == (byte) 0x8b ) //check if matches standard gzip magic number
return new GZIPInputStream( pb );
else
return pb;
}
(Source for the magic number: GZip file format specification)
Update: I've just dicovered that there is also a constant called GZIP_MAGIC
in GZipInputStream
which contains this value, so if you really want to, you can use the lower two bytes of it.