Why import org.apache.commons.lang.StringUtils cannot be imported in android by default.

Do i have to include an external library? Then where can i find that library on the web?

package com.myapps.urlencoding;

import android.app.Activity;
import org.apache.commons.lang.StringUtils;

public class EncodeIdUtil extends Activity {
    /** Called when the activity is first created. */
     private static Long multiplier=Long.parseLong("1zzzz",36);

        /**
         * Encodes the id.
         * @param id the id to encode
         * @return encoded string
         */
        public static String encode(Long id) {
            return StringUtils.reverse(Long.toString((id*multiplier), 35));
        }

        /**
         * Decodes the encoded id.
         * @param encodedId the encodedId to decode
         * @return the Id
         * @throws IllegalArgumentException if encodedId is not a validly encoded id.
         */
        public static Long decode(String encodedId) 
            throws IllegalArgumentException {
            long product;
            try {
                product = Long.parseLong(StringUtils.reverse(encodedId), 35);
            } catch (Exception e) {
                throw new IllegalArgumentException();
            }
            if ( 0 != product % multiplier || product < 0) {
                throw new IllegalArgumentException();
            }
            return product/multiplier;
        }
}