Java converts bytes to hexadecimal code sharing

Some of the code in this article is excerpted from the web and tidy-up for converting between bytes and hexadecimal.

/**
 * reference apache commons <a
 * href="http://commons.apache.org/codec/">http://commons.apache.org/codec/</a>
 * 
 * byte Take up 8 Bit, hexadecimal character occupancy 4 position So we can take one byte Convert to two corresponding hexadecimal characters byte The high 4 And the low 4 position  *  Convert to corresponding hexadecimal characters respectively H and L, And put them together. The same is true for the opposite transformation. 
 * 
 */
public class Hex {
 
  
  private static final char[] DIGITS_LOWER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
      'a', 'b', 'c', 'd', 'e', 'f' };
 
  
  private static final char[] DIGITS_UPPER = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
      'A', 'B', 'C', 'D', 'E', 'F' };
 
  
  public static char[] encodeHex(final byte[] data) {
    return encodeHex(data, true);
  }
 
  /**
   *  Converts a byte array to a hexadecimal character array. 
   * 
   *  Returns because two characters represent a byte char[] Length will be the parameter byte[] Twice the length. 
   * 
   * @param data
   *       Used to convert to hexadecimal characters byte[]
   * @param toLowerCase
   *      <code>true</code>  Convert to lowercase   .  <code>false</code>  Transfer to uppercase 
   * @return  Containing hexadecimal characters char[]
   */
  public static char[] encodeHex(final byte[] data, final boolean toLowerCase) {
    return encodeHex(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
  }
 
  
  protected static char[] encodeHex(final byte[] data, final char[] toDigits) {
    int l = data.length;
    char[] out = new char[l << 1];
    // two characters form the hex value.
    for (int i = 0, j = 0; i < l; i++) {
      out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
      out[j++] = toDigits[0x0F & data[i]];
    }
    return out;
  }
 
  
  public static String encodeHexStr(final byte[] data) {
    return encodeHexStr(data, true);
  }
 
  /**
   *  Converts a byte array to a hexadecimal string. 
   * 
   *  Because two characters represent a byte, the length of the returned string will be an argument byte[] Twice the length. 
   * 
   * @param data
   *       Used to convert to hexadecimal characters byte[]
   * @param toLowerCase
   *      <code>true</code>  Convert to lowercase   .  <code>false</code>  Transfer to uppercase 
   * @return  Hexadecimal string 
   */
  public static String encodeHexStr(byte[] data, boolean toLowerCase) {
    return encodeHexStr(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
  }
 
  
  protected static String encodeHexStr(byte[] data, char[] toDigits) {
    return new String(encodeHex(data, toDigits));
  }
 
  
  public static byte[] decodeHex(char[] data) {
    int len = data.length;
 
    if ((len & 0x01) != 0) {
      throw new RuntimeException("Odd number of characters.");
    }
 
    //A byte corresponds to two hexadecimal characters, and the byte[] size is set to half the size of the char[]
    byte[] out = new byte[len >> 1];
 
    // two characters form the hex value.
    for (int i = 0, j = 0; j < len; i++) {
      int f = toDigit(data[j], j) << 4;
      j++;
      f = f | toDigit(data[j], j);
      j++;
      out[i] = (byte) (f & 0xFF);
    }
 
    return out;
  }
 
  
  protected static int toDigit(final char ch, final int index) {
    final int digit = Character.digit(ch, 16);
    if (digit == -1) {
      throw new RuntimeException("Illegal hexadecimal character " + ch + " at index " + index);
    }
    return digit;
  }
 
  public static void main(String[] args) {
    String srcStr = "HelloWorld!";
    String encodeStr = encodeHexStr(srcStr.getBytes(), false);
    String decodeStr = new String(decodeHex(encodeStr.toCharArray()));
    System.out.println(" Source string: " + srcStr);
    System.out.println(" String encoded in hexadecimal: " + encodeStr);
    System.out.println(" Hexadecimal decoding as a string: " + decodeStr);
  }
 
}