HashService.java

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class HashService {

    public static char[] HEX_CHARS = new char[] {
      '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D',
      'E', 'F'};

  /**
   * Computes the MD5 hash for the specified byte array.
   *
   * @return a big fat string encoding of the MD5 for the content, suitably
   *         formatted for use as a file name
   */
  public static String getMD5Hash(byte[] content) {
    MessageDigest md5;
    try {
      md5 = MessageDigest.getInstance("MD5");
    } catch (NoSuchAlgorithmException e) {
      throw new RuntimeException("Error initializing MD5", e);
    }

    md5.update(content);
    return toHexString(md5.digest());
  }


  /**
   * Returns a string representation of the byte array as a series of
   * hexadecimal characters.
   *
   * @param bytes byte array to convert
   * @return a string representation of the byte array as a series of
   *         hexadecimal characters
   */
  public static String toHexString(byte[] bytes) {
    char[] hexString = new char[2 * bytes.length];
    int j = 0;
    for (int i = 0; i < bytes.length; i++) {
      hexString[j++] = HEX_CHARS[(bytes[i] & 0xF0) >> 4];
      hexString[j++] = HEX_CHARS[bytes[i] & 0x0F];
    }
    return new String(hexString);
  }
}