Question: 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;
        }
}

```

Answer: 
Apache Commons lang is a separate library. You can find it [here](http://commons.apache.org/lang/).
If you are using Android Studio try to use workflow provided to add dependencies rather than manually adding the downloaded library or manually changing gradle files. 

1. File -> Project Structure -> Modules -> app -> Dependencies Tab
2. Click '+' in the bottom left corner and select "Library dependency"
3. In the search field type: "org.apache.commons:commons-lang3" and click Search
4. Select "org.apache.commons:commons-lang3:3.7"

[![enter image description here](https://i.stack.imgur.com/XFSMO.png)](https://i.stack.imgur.com/XFSMO.png)