Convert a hexidecimal string generated by toHexString() back into a byte array. : String vs Byte Array « Data Type « Java Tutorial

1. Java Tutorial
2. Data Type
3. String vs Byte Array

import java.io.IOException;
import java.io.InputStream;
import java.util.Enumeration;
import java.util.Locale;
import java.util.Properties;

/*

   Derby - Class org.apache.derby.iapi.util.PropertyUtil

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to you under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.

 */



public class Main {

  private static char[] hex_table = {
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
    'a', 'b', 'c', 'd', 'e', 'f'
};
  
  /**
    Convert a hexidecimal string generated by toHexString() back
    into a byte array.

    @param s String to convert
    @param offset starting character (zero based) to convert.
    @param length number of characters to convert.

    @return the converted byte array. Returns null if the length is
    not a multiple of 2.
  */
  public static byte[] fromHexString(String s, int offset, int length)
  {
    if ((length%2) != 0)
      return null;

    byte[] byteArray = new byte[length/2];

    int j = 0;
    int end = offset+length;
    for (int i = offset; i < end; i += 2)
    {
      int high_nibble = Character.digit(s.charAt(i), 16);
      int low_nibble = Character.digit(s.charAt(i+1), 16);

      if (high_nibble == -1 || low_nibble == -1)
      {
        // illegal format
        return null;
      }

      byteArray[j++] = (byte)(((high_nibble << 4) & 0xf0) | (low_nibble & 0x0f));
    }
    return byteArray;
  }

}