java实现MD5

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

public class MD5 {

  private final static String[] hexDigits = {
      "0", "1", "2", "3", "4", "5", "6", "7",
      "8", "9", "a", "b", "c", "d", "e", "f"};

  public static String byteArrayToHexString(byte[] b) {
    StringBuffer resultSb = new StringBuffer();
    for (int i = 0; i < b.length; i++) {
      resultSb.append(byteToHexString(b[i]));
    }
    return resultSb.toString();
  }

  private static String byteToHexString(byte b) {
    int n = b;
    if (n < 0)
      n = 256 + n;
    int d1 = n / 16;
    int d2 = n % 16;
    return hexDigits[d1] + hexDigits[d2];
  }

  public static String MD5Encode(String origin) {
    String resultString = null;

    try {
      resultString=new String(origin);
      MessageDigest md = MessageDigest.getInstance("MD5");
      resultString=byteArrayToHexString(md.digest(resultString.getBytes()));
    }
    catch (Exception ex) {

    }
    return resultString;
  }

  public static void main(String[] args){
    System.err.println(MD5Encode("a"));
  }
}