md5加密的工具类（from 韩顺平）

输入一个字符串，然后可以进行md5加密

import java.security.*;
import java.security.spec.*;
public class MyTools {
	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;
		   }
	}
}