20190903 On Java8 Chapter XVI of code check

Chapter XVII file

In Java7 in on the action file introduces huge improvements. These new elements are placed in java.nio.filethe package below, in the past it usually niois nunderstood as newthat is the new io, should now be treated as non-blockinga non-blocking io (io is the input / output I / O).

File operations two basic components:

1. File or directory path;
2. File itself.

File and directory paths

Paths

An Pathobject represents a file or directory path, abstract a cross-operating system (OS) and a file system, aimed at constructing a path without paying attention to the underlying operating system, the code can be run on different operating without modification of on the system. java.nio.file.PathsOverload class contains a method static get(), which accepts a series of Strings string or a Uniform Resource Identifier (URI) as an argument, and returns a conversion Pathobject.

Partial fragment selected path

public class PartsOfPaths {
    public static void main(String[] args) {
        System.out.println(System.getProperty("os.name"));
        Path p = Paths.get("PartsOfPaths.java").toAbsolutePath();
        for (int i = 0; i < p.getNameCount(); i++)
            System.out.println(p.getName(i));
        System.out.println("ends with '.java': " + p.endsWith(".java"));
        for (Path pp : p) {
            System.out.print(pp + ": ");
            System.out.print(p.startsWith(pp) + " : ");
            System.out.println(p.endsWith(pp));
        }
        System.out.println("Starts with " + p.getRoot() + " " + p.startsWith(p.getRoot()));
    }
}

You can getName()be indexed Patheach part until it reaches the upper limit getNameCount(). PathAlso inherited the Iterableinterface, we can traverse through enhanced for loop. Please note that even if the path to ending .java, using endsWith()also the method returns false . This is because endsWith()the comparison is part of the entire path, the file will not contain a suffix path. By using startsWith()and endsWith()can be completed traverse path. But we can see that traverse the Path object does not contain the root path, only the use of startsWith()return will detect when the root path to true .

Path Analysis

FilesThe method includes a full range of tools used to obtain Pathrelevant information.

Paths increase or decrease modification

public class AddAndSubtractPaths {
    static Path base = Paths.get("..", "..", "..").toAbsolutePath().normalize();

    static void show(int id, Path result) {
        if (result.isAbsolute())
            System.out.println("(" + id + ")r " + base.relativize(result));
        else
            System.out.println("(" + id + ")  " + result);
        try {
            System.out.println("RealPath: " + result.toRealPath());
        } catch (IOException e) {
            System.out.println(e);
        }
    }

    public static void main(String[] args) {
        System.out.println(System.getProperty("os.name"));
        System.out.println(base);
        Path p = Paths.get("src","files","AddAndSubtractPaths.java").toAbsolutePath();
        show(1, p);
        Path convoluted = p.getParent().getParent().resolve("strings").resolve("..")
                .resolve(p.getParent().getFileName());
        show(2, convoluted);
        show(3, convoluted.normalize());

        Path p2 = Paths.get("..", "..");
        show(4, p2);
        show(5, p2.normalize());
        show(6, p2.toAbsolutePath().normalize());

        Path p3 = Paths.get(".").toAbsolutePath();
        Path p4 = p3.resolve(p2);
        show(7, p4);
        show(8, p4.normalize());

        Path p5 = Paths.get("").toAbsolutePath();
        show(9, p5);
        show(10, p5.resolveSibling("strings"));
        show(11, Paths.get("nonexistent"));
    }
}

table of Contents

Delete a file or directory:

public class RmDir {
    public static void rmdir(Path dir) throws IOException {
        Files.walkFileTree(dir, new SimpleFileVisitor<Path>() {
            @Override
            public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
                Files.delete(file);
                return FileVisitResult.CONTINUE;
            }

            @Override
            public FileVisitResult postVisitDirectory(Path dir, IOException exc) throws IOException {
                Files.delete(dir);
                return FileVisitResult.CONTINUE;
            }
        });
    }
}

File system

Use FileSystemstools to obtain a "default" file system. "

public class FileSystemDemo {
    static void show(String id, Object o) {
        System.out.println(id + ": " + o);
    }

    public static void main(String[] args) {
        System.out.println(System.getProperty("os.name"));
        FileSystem fsys = FileSystems.getDefault();
        for (FileStore fs : fsys.getFileStores())
            show("File Store", fs);
        for (Path rd : fsys.getRootDirectories())
            show("Root Directory", rd);
        show("Separator", fsys.getSeparator());
        show("UserPrincipalLookupService", fsys.getUserPrincipalLookupService());
        show("isOpen", fsys.isOpen());
        show("isReadOnly", fsys.isReadOnly());
        show("FileSystemProvider", fsys.provider());
        show("File Attribute Views", fsys.supportedFileAttributeViews());
    }
}

Path monitor

By WatchServiceresponding to changes in the directory you can set up a process.

File search

By FileSystemcalling on the object getPathMatcher()to get a PathMatcher, then pass mode you are interested in. Mode has two options: globand regex.

File read and write

Files.readAllLines()Once read the entire file (Therefore, the "small" file is necessary), to produce a List<String>. There is a readAllLines()heavy-duty version, which contains a Charsetparameter to Unicode encoded file is stored.

Files.write()Overload is written to bytethe array, or any Iterable object (which is also Charset option).

Files.lines()Easily convert the file to the line Stream.