How to check if InputStream is Gzipped?

Question

Is there any way to check if InputStream has been gzipped? Here\'s the code:

public static InputStream decompressStream(InputStream input) {
    try {
               


        

Answer 1

I found this useful example that provides a clean implementation of isCompressed():

/*
 * Determines if a byte array is compressed. The java.util.zip GZip
 * implementation does not expose the GZip header so it is difficult to determine
 * if a string is compressed.
 * 
 * @param bytes an array of bytes
 * @return true if the array is compressed or false otherwise
 * @throws java.io.IOException if the byte array couldn't be read
 */
 public boolean isCompressed(byte[] bytes)
 {
      if ((bytes == null) || (bytes.length < 2))
      {
           return false;
      }
      else
      {
            return ((bytes[0] == (byte) (GZIPInputStream.GZIP_MAGIC)) && (bytes[1] == (byte) (GZIPInputStream.GZIP_MAGIC >> 8)));
      }
 }

I tested it with success:

@Test
public void testIsCompressed() {
    assertFalse(util.isCompressed(originalBytes));
    assertTrue(util.isCompressed(compressed));
}