Java Decompress a string compressed with zlib deflate

Question

As the title says. How do you decompress a compressed string which was compressed with zlib deflate? What is the solid way of doing it with an explanation?

Answer 1

Try this - it is a minimal working example:

package zlib.example;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.util.Arrays;
import java.util.zip.Deflater;
import java.util.zip.DeflaterOutputStream;
import java.util.zip.InflaterInputStream;

/**
 * Created by keocra on 08.10.15.
 */
public class Main {
    private final static String inputStr = "Hello World!";

    public static void main(String[] args) throws Exception {
        System.out.println("Will zlib compress following string: " + inputStr);

        // will compress "Hello World!"
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        DeflaterOutputStream dos = new DeflaterOutputStream(baos);
        dos.write(inputStr.getBytes());
        dos.flush();
        dos.close();

        // at this moment baos.toByteArray() holds the compressed data of "Hello World!"

        // will decompress compressed "Hello World!"
        ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray());
        InflaterInputStream iis = new InflaterInputStream(bais);

        String result = "";
        byte[] buf = new byte[5];
        int rlen = -1;
        while ((rlen = iis.read(buf)) != -1) {
            result += new String(Arrays.copyOf(buf, rlen));
        }

        // now result will contain "Hello World!"

        System.out.println("Decompress result: " + result);
    }
}

You should also easily be able to extend this example to compress/decompress files.

Hope it helps ;-)

Further readings:

• http://docs.oracle.com/javase/7/docs/api/java/util/zip/DeflaterOutputStream.html
• https://docs.oracle.com/javase/7/docs/api/java/util/zip/InflaterInputStream.html