public class MD5Digest
{

    private MessageDigest __md5 = null;
    private StringBuffer __digestBuffer = null;

    public MD5Digest()
        throws NoSuchAlgorithmException
    {
        __md5 = MessageDigest.getInstance("MD5");
        __digestBuffer = new StringBuffer();
    }

    public String md5crypt(String s)
    {
        __digestBuffer.setLength(0);
        byte abyte0[] = __md5.digest(s.getBytes());
        for(int i = 0; i < abyte0.length; i++)
            __digestBuffer.append(toHex(abyte0[i]));

        return __digestBuffer.toString();
    }
    public String toHex(byte one){
   String HEX="0123456789ABCDEF";
   char[] result=new char[2];
   result[0]=HEX.charAt((one & 0xf0) >> 4);
   result[1]=HEX.charAt(one & 0x0f);
   String mm=new String(result);
   return mm;
  }
}

--------------------------------------------------------------------------------
/************************************************
MD5 算法的Java Bean
@author:Topcat Tuppin
Last Modified:10,Mar,2001
*************************************************/
package beartool;
import java.lang.reflect.*;
/*************************************************
md5 类实现了RSA Data Security, Inc.在提交给IETF
的RFC1321中的MD5 message-digest 算法。
*************************************************/

public class MD5 {
/* 下面这些S11-S44实际上是一个4*4的矩阵，在原始的C实现中是用#define 实现的，
这里把它们实现成为static final是表示了只读，切能在同一个进程空间内的多个
Instance间共享*/
        static final int S11 = 7;
        static final int S12 = 12;
        static final int S13 = 17;
        static final int S14 = 22;

        static final int S21 = 5;
        static final int S22 = 9;
        static final int S23 = 14;
        static final int S24 = 20;