Information shortener, can be used for shorten info like urls.

InfoShortener.java

/**
 * Abstract generic info shortener that can be modified
 * to generate short ids for desired classes. 
 * 
 * @author eaorak
 */
public abstract class InfoShortener<T> {

    private static int    ALPCNT = 62;
    private static String cstr   = new String();
    private final int     threshold;

    static {
        for (int i = '0'; i <= 'z'; i++) {
            if (Character.isAlphabetic(i) || Character.isDigit(i)) {
                cstr += (char) i;
            }
        }
    }

    /**
     * @param threshold Minimum number to start
     */
    public InfoShortener(int threshold) {
        this.threshold = threshold;
    }

    /**
     * Shorten given string info.
     * 
     * @param str String to shorten
     * @return Shortened info string
     */
    public String shorten(String str) {
        return this.convertToStr(this.getIdFor(str) + this.threshold);
    }

    /**
     * Reverse given shortened info to actual one.
     * 
     * @param str Shortened info string
     * @return Actual info string
     */
    public T reverse(String str) {
        return this.getInfoFor(this.convertToId(str) - this.threshold);
    }

    protected abstract long getIdFor(String str);

    protected abstract T getInfoFor(long id);

    protected long convertToId(String str) {
        long num = 0;
        for (int i = 0; i < str.length(); i++) {
            num += Math.pow(ALPCNT, i) * this.cstr.indexOf(str.charAt(i));
        }
        return num;
    }

    protected String convertToStr(long id) {
        StringBuilder str = new StringBuilder();
        while (id > 0) {
            long x = id % ALPCNT;
            id = (id - x) / ALPCNT;
            str.append(cstr.charAt((int) x));
        }
        return str.toString();
    }

}

SampleGenerator.java

/**
 * Sample class that extends InfoShortener to generate shortened strings 
 * for Camera serial numbers, then back to Camera objects.
 */
public class SampleGenerator extends InfoShortener<Camera> {

    public SampleGenerator() {
        super(1000);
    }

    @Override
    protected long getIdFor(String str) {
        // Find camera object with serial (str) from database
        Camera camera = Camera.find("serial_no = ?", str).first();
        if (camera == null) {
            throw new RuntimeException("No camera could be found with serial number: " + str);
        }
        return camera.getId();
    }

    @Override
    protected Camera getInfoFor(long id) {
        // Find camera object with given id from database
        Camera camera = Camera.findById(id);
        if (camera == null) {
            throw new RuntimeException("No camera could be found with id: " + id);
        }
        return camera;
    }

    // Sample execution
    public static void main(String[] args) {
        SampleGenerator gen = new SampleGenerator();
        String shortened = gen.shorten("29jd37hd39dehbv");
        System.out.println(shortened);
        // 9G
        System.out.println(gen.reverse(shortened));
        // Camera [serialNo=29jd37hd39dehbv, model=cm512, status=ACTIVE]
    }

}