NIO.2 review of java

Following on from java IO and NIO, review NIO.2. !!

IO : https://qiita.com/liguofeng29/items/e08dc21b16c0057f601e NIO : https://qiita.com/liguofeng29/items/c827af3d62f219e17755

What is NIO.2?

Simply put, it is an improvement over the existing NIO.

1. Enhanced FileIO
2. Enhanced IO based on asynchronous Channle

FileIO enhancement

Core API

Chat: Paths and Files follow java's consistent naming conventions.

• Paths, Path utility class
• While saying the utility class __ of Files, File, the argument was almost Path! !! __
• Arrays, Array utility class
• Collections, Collection Utility Classes
• Objects, Object utility class

Path, Paths

Path sample(I wanted to get it with markdown)

private static void showPath(Path path) {
    System.out.println("|Acquisition contents|result|");
    System.out.println("|---|---|");
    System.out.printf("|%s | %s |\r\n", "Element count", path.getNameCount());
    System.out.printf("|%s | %s |\r\n", "Specified element name", path.getName(0));
    System.out.printf("|%s | %s |\r\n", "file name", path.getFileName());
    System.out.printf("|%s | %s |\r\n", "File system name", path.getFileSystem());
    System.out.printf("|%s | %s |\r\n", "parent", path.getParent());
    System.out.printf("|%s | %s |\r\n", "root", path.getRoot());
    System.out.printf("|%s | %s |\r\n", "Is it an absolute pass?", path.isAbsolute());
}

Path,Paths

private static void path_test() {
    //Relative path
    Path relativePath = Paths.get(".", "NIO2", "sub", "nio2-file.txt");
    System.out.println("----Relative path----");
    showPath(relativePath);
    //Absolute path
    System.out.println("----Absolute path----");
    showPath(relativePath.toAbsolutePath());
}

• Relative path

• Absolute path

1. The result to be obtained differs depending on the absolute path and relative path.
2. sun.nio.fs.WindowsFileSystem, which makes __ "platform independent" __?
3. Get a Path instance from Paths # get (__File to Path, Path to File is also possible __)

Files

Files sample

nio2-src.txt

1st line, AIC
Second line, UTF-8?
3rd line

Files sample(I wanted to get it with markdown)

private static void testFiles(Path path) {
    System.out.println("|Acquisition contents|result|");
    System.out.println("|---|---|");
    try {
        System.out.printf("|%s | %s |\r\n", "Is it a directory?", Files.isDirectory(path));
        System.out.printf("|%s | %s |\r\n", "Hidden", Files.isHidden(path));
        System.out.printf("|%s | %s |\r\n", "Is it a directory?", Files.isWritable(path));
        System.out.printf("|%s | %s |\r\n", "The size is", Files.size(path));
        System.out.printf("|%s | " , "Get file contents");
        Files.lines(path).forEach(line -> {
            System.out.printf("%s<br>" , line);
        });
        System.out.printf("|\r\n");
        System.out.printf("|%s | " , "Get directory elements");
        Files.list(path.getParent()).forEach(p -> {
            System.out.printf("%s<br>" , p);
        });
        System.out.printf("|\r\n");
        System.out.printf("|%s | %s |\r\n", "Storage capacity", Files.getFileStore(path).getTotalSpace() / 1024 / 1024 / 1024 + "GB");
        System.out.printf("|%s | %s |\r\n", "Available capacity", Files.getFileStore(path).getUsableSpace() / 1024 / 1024 / 1024 + "GB");
        System.out.printf("|%s | %s |\r\n", "Unallocated capacity", Files.getFileStore(path).getUnallocatedSpace() / 1024 / 1024 / 1024 + "GB");
        System.out.printf("|%s | %s |\r\n", "Does it exist", Files.exists(path));
        Files.delete(path);
        System.out.printf("|%s | %s |\r\n", "delete", "Deleted");
        System.out.printf("|%s | %s |\r\n", "Does it exist", Files.exists(path));
    } catch (IOException e) {
        e.printStackTrace();
    }
}

File#WalkTree With existing IO, I had to implement recursive scanning myself, and the code was complicated and not easy to use.

In 1.7, Files # walkFileTree allows recursive scanning.

There were samples of walkFileTree here and there, so I'll omit them!

Files#walk In 1.8, Files # walk is convenient!

Files.walk

Files.walk(Paths.get(".", "NIO2"), FileVisitOption.FOLLOW_LINKS)
    //Swap directory and file
    .sorted(Comparator.reverseOrder())
    //Confirmation of deletion target
    .peek(System.out::println)
    //Delete
    .forEach(path -> {
        try {
            Files.delete(path);
        } catch (IOException e) {
            e.printStackTrace();
        }
    });

Other

WatchService It is a mechanism to monitor File changes. In the traditional way, possible implementations

1. Launch another thread
2. Save the state
3. Scan at regular intervals and compare with the previous state

You can easily create files with WatchService.

WatchService sample

try {
    WatchService watchService = FileSystems.getDefault().newWatchService();
    Paths.get(".").register(
        watchService,
        StandardWatchEventKinds.ENTRY_CREATE, //CREATE monitor
        StandardWatchEventKinds.ENTRY_DELETE, //DELETE monitoring
        StandardWatchEventKinds.ENTRY_MODIFY  //MODIFY monitoring
    );
    System.out.println("-----watch start-----");
    while (true) {
        //Keep waiting
        WatchKey key = watchService.take();
        key.pollEvents().stream()
            .forEach(
                watchEvent -> {
                    System.out.println("Type of occurrence: " + watchEvent.kind().name());
                    System.out.println("Target name: " + watchEvent.context());
                });
        //Next monitoring
        if (!key.reset()) {
            break;
        }
    }
} catch (IOException | InterruptedException e) {
    e.printStackTrace();
}

1. Generate WatchService
2. Register WatchService and monitor contents
3. Get WatchKey

• take (): Keep waiting until you get WatchKey
• poll (): Get WatchKey, otherwise null
• poll (long timeout, TimeUnit unit): Wait for timeout

4. Processing
5. WatchKey reset

Attribute read / write

Roughly, it is an implementation of FileAttributeView, and it seems that you can operate detailed attributes.

• AclFileAttributeView
• BasicFileAttributeView
• DocFileAttributeView
• FileOnwerFileAttributeView
• PosixFileFileAttributeView
• UserDefinedFileAttributeView

BasicFileAttributeView sample

Path path = Paths.get(".", "NIO2", "nio2-src.txt");

BasicFileAttributeView view = Files.getFileAttributeView(path, BasicFileAttributeView.class);
BasicFileAttributes attributes = view.readAttributes();

System.out.println("Last access: " + attributes.lastAccessTime());
System.out.println("Latest correction time: " + attributes.lastModifiedTime());