Introduction

On a website project at work i had to implement a feature that allowed the user to download one or more messages as a zip file. When i started, i really was shocked how complicated it is to zip or unzip a String in java. If you glance over to csharp the whole zip-thing looks easy as pie:

string startPath = @"c:examplestart";
string zipPath = @"c:exampleresult.zip";
string extractPath = @"c:exampleextract";

ZipFile.CreateFromDirectory(startPath, zipPath);

ZipFile.ExtractToDirectory(zipPath, extractPath);

Those wrapper classes from System.IO make it really easy to create and read archives. After a bit of trial and error i was able to create some easy to use java methods which do the same. So for you (and for me as a future reference), here’s the code.

Zipping / Unzipping a String

String -> ZIP

Lets have alook at the usual case where you need to zip a String.

public static byte[] zip(String s) throws IOException {
    Deflater compressor = new Deflater();
    ByteArrayOutputStream boas = new ByteArrayOutputStream();
    try {
        compressor.setInput(s.getBytes("UTF8"));
        compressor.finish();
        byte[] buf = new byte[1024];
        while (!compressor.finished()) {
            int count = compressor.deflate(buf);
            boas.write(buf, 0, count);
        }
    } finally {
        compressor.end();
    }
    return boas.toByteArray();
}

ZIP -> String

The code is really straight forward, but it looks ugly and you will possibly just copy & paste it into your project like almost the rest of the world, so why not create an easy to use API (I’m looking at you, Oracle ಠ_ಠ)?

Zipping / Unzipping several files

List -> ZIP

Sometimes you want to create a ZIP file just to combine several files to one archive as a usability feature to the users of your application.

The Map parameter carries the Strings you need to be zipped. The first String is the filename that should appear inside the ZIP file and the second String is the content of that file.

ZIP -> List

Same here, you provide an archive and get a Map with the files it contained. Again, the first String is the filename and the second String is the file content.

Conclusion

As you can see the whole thing is not really complicated but you wouldn’t be able to write the code without googling. Well, that’s what APIs are for, so lets hope, that in near future there will be a more pleasant way to zip and unzip files in java.

You can have a look at the whole class file in my github repo.

Happy coding!