/**
     * Encode a string using algorithm specified in web.xml and return the
     * resulting encrypted password. If exception, the plain credentials
     * string is returned
     *
     * @param password Password or other credentials to use in authenticating
     *        this username
     * @param algorithm Algorithm used to do the digest(加密算法：MD5,SHA)
     *
     * @return encypted password based on the algorithm.
     */
    public static String encodePassword(String password, String algorithm) {
        byte[] unencodedPassword = password.getBytes();
        
        MessageDigest md = null;
        
        try {
            // first create an instance, given the provider
            md = MessageDigest.getInstance(algorithm);
        } catch (Exception e) {
            mLogger.error("Exception: " + e);
            return password;
        }
        
        md.reset();
        
        // call the update method one or more times
        // (useful when you don't know the size of your data, eg. stream)
        md.update(unencodedPassword);
        
        // now calculate the hash
        byte[] encodedPassword = md.digest();
        
        StringBuffer buf = new StringBuffer();
        
        for (int i = 0; i < encodedPassword.length; i++) {
            if ((encodedPassword[i] & 0xff) < 0x10) {
                buf.append("0");
            }
            
            buf.append(Long.toString(encodedPassword[i] & 0xff, 16));
        }
        
        return buf.toString();
    }
    
    /**
     * Encode a string using Base64 encoding. Used when storing passwords
     * as cookies.
     *
     * This is weak encoding in that anyone can use the decodeString
     * routine to reverse the encoding.
     *
     * @param str
     * @return String
     * @throws IOException
     */
    public static String encodeString(String str) throws IOException {
        Base64 base64 = new Base64();
        String encodedStr = new String(base64.encodeBase64(str.getBytes()));        
        return (encodedStr.trim());
    }
    
    /**
     * Decode a string using Base64 encoding.
     *
     * @param str
     * @return String
     * @throws IOException
     */
    public static String decodeString(String str) throws IOException {
        Base64 base64 = new Base64();
        String value = new String(base64.decodeBase64(str.getBytes()));        
        return (value);
    }