not getting exact result when converting byte array to hex in java

Question

I'm trying to get hex string value from bytebuffer using below code. Reference: In Java, how do I convert a byte array to a string of hex digits while keeping leading zeros?

    public ByteBuffer convert(ByteBuffer in) {
    StringBuffer out = new StringBuffer();
    for (int iter = 0; iter < in.array().length; iter++) {
      byte high = (byte) ( (in.array()[iter] & 0xf0) >> 4);
      byte low =  (byte)   (in.array()[iter] & 0x0f);
      out.append(nibble2char(low));
      out.append(nibble2char(high));
    }
    return ByteBuffer.wrap(out.reverse().toString().getBytes());
   }
   private static char nibble2char(byte b) {
   byte nibble = (byte) (b & 0x0f);
   if (nibble < 10) {
     return (char) ('0' + nibble);
   }
   return (char) ('a' + nibble - 10);
  }

The value I got as 701000000000, Actually I'm expecting a value like this 000000000107. So I called a reverse method on stringbuffer object at the time of wrapping.

After this I'm always getting "ffffff000000" Can someone please help me on this.