DevTut

# New File I/O

# Manipulating paths

# Joining Two Paths

Paths can be joined using the resolve() method. The path passed has to be a partial path, which is a path that doesn't include the root element.

Path p5 = Paths.get("/home/");
Path p6 = Paths.get("arthur/files");
Path joined = p5.resolve(p6);
Path otherJoined = p5.resolve("ford/files");


joined.toString() == "/home/arthur/files"
otherJoined.toString() == "/home/ford/files"

# Normalizing a path

Paths may contain the elements . (which points to the directory you're currently in) and ..(which points to the parent directory).

When used in a path, . can be removed at any time without changing the path's destination, and .. can be removed together with the preceding element.

With the Paths API, this is done using the .normalize() method:

Path p7 = Paths.get("/home/./arthur/../ford/files");
Path p8 = Paths.get("C:\\Users\\.\\..\\Program Files");


p7.normalize().toString() == "/home/ford/files"
p8.normalize().toString() == "C:\\Program Files"

# Creating paths

The Path class is used to programmaticaly represent a path in the file system (and can therefore point to files as well as directories, even to non-existent ones)

A path can be obtained using the helper class Paths:

Path p1 = Paths.get("/var/www");
Path p2 = Paths.get(URI.create("file:///home/testuser/File.txt"));
Path p3 = Paths.get("C:\\Users\\DentAr\\Documents\\HHGTDG.odt");
Path p4 = Paths.get("/home", "arthur", "files", "diary.tex");

# Retrieving information about a path

Information about a path can be get using the methods of a Path object:

  • `toString()` returns the string representation of the path 
    Path p1 = Paths.get("/var/www"); // p1.toString() returns "/var/www"
  • `getFileName()` returns the file name (or, more specifically, the last element of the path 
    Path p1 = Paths.get("/var/www"); // p1.getFileName() returns "www"
Path p3 = Paths.get("C:\\Users\\DentAr\\Documents\\HHGTDG.odt"); // p3.getFileName() returns "HHGTDG.odt"
  • `getNameCount()` returns the number of elements that form the path 
    Path p1 = Paths.get("/var/www"); // p1.getNameCount() returns 2
  • `getName(int index)` returns the element at the given index 
    Path p1 = Paths.get("/var/www"); // p1.getName(0) returns "var", p1.getName(1) returns "www"
  • `getParent()` returns the path of the parent directory 
    Path p1 = Paths.get("/var/www"); // p1.getParent().toString() returns "/var"
  • `getRoot()` returns the root of the path 
    Path p1 = Paths.get("/var/www"); // p1.getRoot().toString() returns "/"
Path p3 = Paths.get("C:\\Users\\DentAr\\Documents\\HHGTDG.odt"); // p3.getRoot().toString() returns "C:\\"

    • # Retrieving information using the filesystem

    To interact with the filesystem you use the methods of the class Files.

    # Checking existence

    To check the existence of the file or directory a path points to, you use the following methods:

    Files.exists(Path path)

    and

    Files.notExists(Path path)

    !Files.exists(path) does not neccesarily have to be equal to Files.notExists(path), because there are three possible scenarios:

    • A file's or directory's existence is verified (exists returns true and notExists returns false in this case)
    • A file's or directory's nonexistence is verfied (exists returns false and notExists returns true)
    • Neither the existence nor the nonexistence of a file or a directory can be verified (for example due to access restrictions): Both exists and nonExists return false.

    # Checking whether a path points to a file or a directory

    This is done using Files.isDirectory(Path path) and Files.isRegularFile(Path path)

    Path p1 = Paths.get("/var/www");
Path p2 = Paths.get("/home/testuser/File.txt");


    Files.isDirectory(p1) == true
Files.isRegularFile(p1) == false

Files.isDirectory(p2) == false
Files.isRegularFile(p2) == true

    # Getting properties

    This can be done using the following methods:

    Files.isReadable(Path path)
Files.isWritable(Path path)
Files.isExecutable(Path path)

Files.isHidden(Path path)
Files.isSymbolicLink(Path path)

    # Getting MIME type

    Files.probeContentType(Path path)

    This tries to get the MIME type of a file. It returns a MIME type String, like this:

    • text/plain for text files
    • text/html for HTML pages
    • application/pdf for PDF files
    • image/png for PNG files

    # Reading files

    Files can be read byte- and line-wise using the Files class.

    Path p2 = Paths.get(URI.create("file:///home/testuser/File.txt"));
byte[] content = Files.readAllBytes(p2);
List<String> linesOfContent = Files.readAllLines(p2);

    Files.readAllLines() optionally takes a charset as parameter (default is StandardCharsets.UTF_8):

    List<String> linesOfContent = Files.readAllLines(p2, StandardCharsets.ISO_8859_1);

    # Writing files

    Files can be written bite- and line-wise using the Files class

    Path p2 = Paths.get("/home/testuser/File.txt");
List<String> lines = Arrays.asList(
    new String[]{"First line", "Second line", "Third line"});

Files.write(p2, lines);


    Files.write(Path path, byte[] bytes)

    Existing files wile be overridden, non-existing files will be created.

    # Syntax

    • Paths.get(String first, String... more) // Creates a Path instance by its String elements
    • Paths.get(URI uri) // Creates a Path instance by a URI

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