url编码，只对汉字有效

public static String toUtf8String(String s) {

    StringBuffer sb = new StringBuffer();
    for (int i = 0; i < s.length(); i++) {
        char c = s.charAt(i);
        if (c >= 0 && c <= 255) {
            sb.append(c);
        } else {
            byte[] b;
            try {
                b = String.valueOf(c).getBytes("utf-8");
            } catch (Exception ex) {
                System.out.println(ex);
                b = new byte[0];
            }
            for (int j = 0; j < b.length; j++) {
                int k = b[j];
                if (k < 0)
                    k += 256;
                sb.append("%" + Integer.toHexString(k).toUpperCase());
            }
        }
    }
    return sb.toString();
}