Test.java

package test;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.zip.GZIPInputStream;
import java.util.zip.GZIPOutputStream;

public class Test {

    public static void main(String[] args) {
        String comp = compress("poooooooo");
        System.out.println('"' + comp + '"'); // "af)AAAAAAAv()yVOC")+?~!BAAAA"
        System.out.println('"' + decompress(comp) + '"'); // "poooooooo"
    }

    public static String compress(String input) {
        byte[] data = input.getBytes(StandardCharsets.US_ASCII);
        try {
            ByteArrayOutputStream byteStream = new ByteArrayOutputStream(data.length);
            try (GZIPOutputStream compressStream = new GZIPOutputStream(byteStream)) {
                compressStream.write(data);
            }
            return new String(Base91.encode(byteStream.toByteArray()), StandardCharsets.US_ASCII.name());
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return null;
    }

    public static String decompress(String input) {
        byte[] data = Base91.decode(input.getBytes(StandardCharsets.US_ASCII));
        try (GZIPInputStream compressStream = new GZIPInputStream(new ByteArrayInputStream(data));
                ByteArrayOutputStream byteOutputStream = new ByteArrayOutputStream()) {
            while (compressStream.available() != 0) {
                byteOutputStream.write(compressStream.read());
            }
            return new String(byteOutputStream.toByteArray(), StandardCharsets.US_ASCII);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
        return null;
    }
}