I also faced the need to decompress .Z archives, looked through internet but have found no better answer than mine below. One can use Apache Commons Compress
FileInputStream fin = new FileInputStream("archive.tar.Z");
BufferedInputStream in = new BufferedInputStream(fin);
FileOutputStream out = new FileOutputStream("archive.tar");
ZCompressorInputStream zIn = new ZCompressorInputStream(in);
final byte[] buffer = new byte[buffersize];
int n = 0;
while (-1 != (n = zIn.read(buffer))) {
out.write(buffer, 0, n);
}
out.close();
zIn.close();
Check this link
This really works