In previous post we have explored and wrote a utility class for zipping and unzipping files and folders using java Zip api. Now we will see another api provided by java named FileSystem under java.nio.file.

FileSystem:

FileSystem api of java non-blocking io’s file is an interface to underlying file system. It’s the factory for object to access File and other objects in the file system.

The default file system, obtained by invoking the FileSystems.getDefault() method, provides access to the file system that is accessible to the Java virtual machine. The FileSystems class defines methods to create file systems that provide access to other types of (custom) file systems.

In java there are 3 file system providers.

A provider is a factory for one or more FileSystem instances. Each file system is identified by a URI where the URI’s scheme matches the provider’s scheme. The default file system, for example, is identified by the URI "file:///". A memory-based file system, for example, may be identified by a URI such as "memory:///?name=logfs". The newFileSystem method may be used to create a file system, and the getFileSystem method may be used to obtain a reference to an existing file system created by the provider. Where a provider is the factory for a single file system then it is provider dependent if the file system is created when the provider is initialized, or later when the newFileSystem method is invoked. In the case of the default provider, the FileSystem is created when the provider is initialized.

FileSystemProviders:

A Service-provider class for file systems. A file system provider is a concrete implementation of this class that implements the abstract methods defined by this class. A provider is identified by a URI scheme. The default provider is identified by the URI scheme “file”. It creates the FileSystem that provides access to the file systems accessible to the Java virtual machine. The FileSystems class defines how file system providers are located and loaded. The default provider is typically a system-default provider but may be overridden if the system property java.nio.file.spi.DefaultFileSystemProvider is set. In that case, the provider has a one argument constructor whose formal parameter type is FileSystemProvider. All other providers have a zero argument constructor that initializes the provider.

ZipFileSystemProvider:

The zip file system provider treats a zip or JAR file as a file system and provides the ability to manipulate the contents of the file. The zip file system provider creates multiple file systems — one file system for each zip or JAR file.

ZipFileSystemProvider to create a Folder.zip and archive a single file and a direcotry/folder

Single File to Zip file
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public static void ZipSingleFile(Path source, String fileName) {
            if (!Files.isRegularFile(source)) {
                System.err.println("Please provide a file.");
                return;
            }

            Map<String, String> env = new HashMap<>();
            // Create the zip file if it doesn't exist
            env.put("create", "true");

            URI uri = URI.create("jar:file:/home/mohibulhasan/Documents/" + fileName);

            try (FileSystem zipFileSystem = FileSystems.newFileSystem(uri, env)) {
                Path pathInZipfile = zipFileSystem.getPath(source.getFileName().toString());

                // Copy a file into the zip file path
                Files.copy(source, pathInZipfile, StandardCopyOption.REPLACE_EXISTING);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }

        }
Folder to Zip:
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public static void zipFolder(Path source) throws IOException {

    // get current working directory
    String currentPath = System.getProperty("user.dir") + File.separator;

    // get folder name as zip file name
    // can be other extension, .foo .bar .whatever
    String zipFileName = source.getFileName().toString() + ".zip";
    URI uri = URI.create("jar:file:" + currentPath + zipFileName);

    Files.walkFileTree(source, new SimpleFileVisitor<>() {
        @Override
        public FileVisitResult visitFile(Path file, BasicFileAttributes attributes) {

            // don't copy symboliclink as its not supported
            if (attributes.isSymbolicLink()) {
                return FileVisitResult.CONTINUE;
            }

            Map<String, String> env = new HashMap<>();
            env.put("create", "true");

            try (FileSystem zipfs = FileSystems.newFileSystem(uri, env)) {

                Path targetFile = source.relativize(file);
                Path pathInZipfile = zipfs.getPath(targetFile.toString());

                // NoSuchFileException, need create parent directories in zip path
                if (pathInZipfile.getParent() != null) {
                    Files.createDirectories(pathInZipfile.getParent());
                }

                // copy file attributes
                CopyOption[] options = {StandardCopyOption.REPLACE_EXISTING, StandardCopyOption.COPY_ATTRIBUTES, LinkOption.NOFOLLOW_LINKS};
                // Copy a file into the zip file path
                Files.copy(file, pathInZipfile, options);

            } catch (IOException e) {
                e.printStackTrace();
            }

            return FileVisitResult.CONTINUE;
        }

        @Override
        public FileVisitResult visitFileFailed(Path file, IOException exc) {
            System.err.printf("Unable to zip : %s%n%s%n", file, exc);
            return FileVisitResult.CONTINUE;
        }

    });

}

In this case by accessing and then copying the file from the Folder.zip file to and external folder will behave like unzip.