Java - Zipping and Unzipping

In this quick tutorial, we'll discuss how to zip a file into an archive and how to unzip the archive – all using core libraries provided by Java.

These core libraries are part of the java.util.zip package – where we can find all zipping and unzipping related utilities.

Zip a File

Let's first have a look at a simple operation – zipping a single file.

For our example here we'll zip a file named test1.txt into an archived named compressed.zip.

We'll of course first access the file from disk – let's have a look:

public class ZipFile {
    public static void main(String[] args) throws IOException {
        String sourceFile = "test1.txt";
        FileOutputStream fos = new FileOutputStream("compressed.zip");
        ZipOutputStream zipOut = new ZipOutputStream(fos);
        File fileToZip = new File(sourceFile);
        FileInputStream fis = new FileInputStream(fileToZip);
        ZipEntry zipEntry = new ZipEntry(fileToZip.getName());
        zipOut.putNextEntry(zipEntry);
        byte[] bytes = new byte[1024];
        int length;
        while((length = fis.read(bytes)) >= 0) {
            zipOut.write(bytes, 0, length);
        }
        zipOut.close();
        fis.close();
        fos.close();
    }
}

Zip Multiple Files

Next, let's see how to zip multiple files into one zip file. We will compress test1.txt and test2.txt into multiCompressed.zip:

public class ZipMultipleFiles {
    public static void main(String[] args) throws IOException {
        List srcFiles = Arrays.asList("test1.txt", "test2.txt");
        FileOutputStream fos = new FileOutputStream("multiCompressed.zip");
        ZipOutputStream zipOut = new ZipOutputStream(fos);
        for (String srcFile : srcFiles) {
            File fileToZip = new File(srcFile);
            FileInputStream fis = new FileInputStream(fileToZip);
            ZipEntry zipEntry = new ZipEntry(fileToZip.getName());
            zipOut.putNextEntry(zipEntry);
 
            byte[] bytes = new byte[1024];
            int length;
            while((length = fis.read(bytes)) >= 0) {
                zipOut.write(bytes, 0, length);
            }
            fis.close();
        }
        zipOut.close();
        fos.close();
    }
}

Zip a Directory

Now, let's discuss how to zip an entire directory. We will directory zipTest into dirCompressed.zip 

public class ZipDirectory {
    public static void main(String[] args) throws IOException {
        String sourceFile = "zipTest";
        FileOutputStream fos = new FileOutputStream("dirCompressed.zip");
        ZipOutputStream zipOut = new ZipOutputStream(fos);
        File fileToZip = new File(sourceFile);
 
        zipFile(fileToZip, fileToZip.getName(), zipOut);
        zipOut.close();
        fos.close();
    }
 
    private static void zipFile(File fileToZip, String fileName, ZipOutputStream zipOut) throws IOException {
        if (fileToZip.isHidden()) {
            return;
        }
        if (fileToZip.isDirectory()) {
            if (fileName.endsWith("/")) {
                zipOut.putNextEntry(new ZipEntry(fileName));
                zipOut.closeEntry();
            } else {
                zipOut.putNextEntry(new ZipEntry(fileName + "/"));
                zipOut.closeEntry();
            }
            File[] children = fileToZip.listFiles();
            for (File childFile : children) {
                zipFile(childFile, fileName + "/" + childFile.getName(), zipOut);
            }
            return;
        }
        FileInputStream fis = new FileInputStream(fileToZip);
        ZipEntry zipEntry = new ZipEntry(fileName);
        zipOut.putNextEntry(zipEntry);
        byte[] bytes = new byte[1024];
        int length;
        while ((length = fis.read(bytes)) >= 0) {
            zipOut.write(bytes, 0, length);
        }
        fis.close();
    }
}

Note that:

• To zip sub-directories, we iterate through them recursively.
• Every time we find a directory, we append its name to the descendants ZipEntry name to save the hierarchy.
• We also create a directory entry for every empty directory