Using Java to Zip/Unzip files

There's been a ZipFile class in Java sinds a long time. But nowadays sinds JDK7 there's also a ZipFileSystem which is a bit easier to work with in some cases and can do more things.

Below are two examples, one using ZipFile and one using ZipFileSystem.

Using ZipFile

Unzipping works as follows:

  @Test
  public void testOldZip() throws URISyntaxException, IOException {
    URL resource = UnzipperTest.class.getResource("/test.zip");
    assert resource != null;
    Path path = Path.of(resource.toURI());
    try (var zipFile = new ZipFile(path.toFile())) {
      Enumeration<? extends ZipEntry> entries = zipFile.entries();
      while (entries.hasMoreElements()) {
        ZipEntry nextElement = entries.nextElement();
        if (nextElement.isDirectory()) {
          log.add("File " + nextElement.getName() + " from zipfile is a directory - skipped");
        }
        else if (nextElement.getName().contains("__MACOSX")) {
          log.add("File " + nextElement.getName() + " from zipfile is a MACOS file/dir - skipped");
        }
        else {
          log.add("File " + nextElement.getName() + " retrieved from zip.");
          var filename = nextElement.getName();
          InputStream inputStream = zipFile.getInputStream(nextElement);
          result.add(new FileContents(filename, inputStream.readAllBytes()));
        }
      }
    }
    assertThat(result).hasSize(6);
    assertThat(result.stream().map(x -> x.filename).collect(Collectors.toList())).isEqualTo(
        List.of("test/test1.txt",
            "test/test/ziptest.zip",
            "test/test/ziptest/zippem2.txt",
            "test/test/ziptest/zippem.txt",
            "test/test2/test2.txt",
            "test/test2/text3.xml"));
    assertThat(log).hasSize(11)
        .isEqualTo(List.of("File test/ from zipfile is a directory - skipped",
            "File test/test1.txt retrieved from zip.",
            "File test/test/ from zipfile is a directory - skipped",
            "File test/test/ziptest.zip retrieved from zip.",
            "File test/test/ziptest/ from zipfile is a directory - skipped",
            "File test/test/ziptest/zippem2.txt retrieved from zip.",
            "File test/test/ziptest/zippem.txt retrieved from zip.",
            "File test/test2/ from zipfile is a directory - skipped",
            "File test/test2/test2.txt retrieved from zip.",
            "File test/test2/test3/ from zipfile is a directory - skipped",
            "File test/test2/text3.xml retrieved from zip."));
  }

Using ZipFileSystem

Apparently it is also possible to mount a zip file as a FileSystem (sinds JDK 7).

It's a bit easier to work with, and has less problems with leaking resources/streams, and allows easy editing and removing items from the zip.

On the other hand, some FileSystem operations are not available in a ZipFileSystem, and then you get a UnsupportedOperationException.

  private static class ZipVisitor
      extends SimpleFileVisitor<Path> {

    private final List<FileContents> result;
    private final List<String> log;

    private ZipVisitor(List<FileContents> result, List<String> log) {
      this.result = result;
      this.log = log;
    }

    @Override
    public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
      if (file.toString().contains("__MACOSX")) {
        log.add("File " + file + " from zipfile is a MACOS file/dir - skipped");
        return FileVisitResult.CONTINUE;
      }
      if (Objects.equals(file.toString(), ".DS_Store")) {
        log.add("File " + file + " from zipfile is a .DS_Store file/dir - skipped");
        return FileVisitResult.CONTINUE;
      }
      log.add("File " + file + " retrieved from zip.");
      String filename = file.toString();
      // file.toFile() -> unsupported operation.
      result.add(new FileContents(filename, Files.readAllBytes(file)));
      return FileVisitResult.CONTINUE;
    }
  }

  @Test
  public void testNewZip() throws URISyntaxException, IOException {
    URL resource = UnzipperTest.class.getResource("/test.zip");
    assert resource != null;
    var path = Path.of(resource.toURI());
    try (FileSystem filesystem = FileSystems.newFileSystem(path, Collections.emptyMap())) {
      var rootDirectories = filesystem.getRootDirectories();
      rootDirectories.forEach(root ->
              //walk the zip file tree
          {
            try {
              Files.walkFileTree(root, new ZipVisitor(result, log));
            }
            catch (IOException e) {
              throw new RuntimeException(e);
            }
          }
      );
    }
    assertThat(result).hasSize(6);
    assertThat(result.stream().map(x -> x.filename).collect(Collectors.toList())).isEqualTo(
        List.of("/test/test2/text3.xml",
            "/test/test2/test2.txt",
            "/test/test/ziptest/zippem.txt",
            "/test/test/ziptest/zippem2.txt",
            "/test/test/ziptest.zip",
            "/test/test1.txt"));
    assertThat(log).hasSize(6)
        .isEqualTo(List.of("File /test/test2/text3.xml retrieved from zip.",
            "File /test/test2/test2.txt retrieved from zip.",
            "File /test/test/ziptest/zippem.txt retrieved from zip.",
            "File /test/test/ziptest/zippem2.txt retrieved from zip.",
            "File /test/test/ziptest.zip retrieved from zip.",
            "File /test/test1.txt retrieved from zip."));
  }

References

fahd.blog - Java 7: Working with Zip Files

https://fahdshariff.blogspot.com/2011/08/java-7-working-with-zip-files.html

Oracle Java Documentation - Zip File System Provider

https://docs.oracle.com/javase/8/docs/technotes/guides/io/fsp/zipfilesystemprovider.html