java md5

import java.security.*;import java.security.spec.*;class MD5_test { public final static String MD5(String s) {  char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',    'a', 'b', 'c', 'd', 'e', 'f' };  try {   byte[] strTemp = s.getBytes();   MessageDigest mdTemp = MessageDigest.getInstance("MD5");   mdTemp.update(strTemp);   byte[] md = mdTemp.digest();   int j = md.length;   char str[] = new char[j * 2];   int k = 0;   for (int i = 0; i < j; i++) {    byte byte0 = md[i];    str[k++] = hexDigits[byte0 >>> 4 & 0xf];    str[k++] = hexDigits[byte0 & 0xf];   }   return new String(str);  } catch (Exception e) {   return null;  } } public static void main(String[] args) {  // MD5_Test aa = new MD5_Test();  System.out.print(MD5_test.MD5("b")); }}