New File I/O
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
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 pathPath p1 = Paths.get("/var/www"); // p1.toString() returns "/var/www"
-
getFileName()
returns the file name (or, more specifically, the last element of the pathPath 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 pathPath p1 = Paths.get("/var/www"); // p1.getNameCount() returns 2
-
getName(int index)
returns the element at the given indexPath p1 = Paths.get("/var/www"); // p1.getName(0) returns "var", p1.getName(1) returns "www"
-
getParent()
returns the path of the parent directoryPath p1 = Paths.get("/var/www"); // p1.getParent().toString() returns "/var"
-
getRoot()
returns the root of the pathPath p1 = Paths.get("/var/www"); // p1.getRoot().toString() returns "/" Path p3 = Paths.get("C:\\Users\\DentAr\\Documents\\HHGTDG.odt"); // p3.getRoot().toString() returns "C:\\"
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"
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
returnstrue
andnotExists
returnsfalse
in this case) - A file’s or directory’s nonexistence is verfied (
exists
returnsfalse
andnotExists
returnstrue
) - Neither the existence nor the nonexistence of a file or a directory can be verified (for example due to access restrictions): Both
exists
andnonExists
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 filestext/html
for HTML pagesapplication/pdf
for PDF filesimage/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.