Lesson 10 Java File I/O (NIO.2)

Path interface to operate on file and directory paths
Use the

limited set of
file attributes
Performance issues
Scalability issues
Very basic

represented by a path, which is the relative or absolute

root node: / (Solaris) C:\ (Windows)

Admin

Documents and Settings

labs

student

finance.xls

logfile.txt

absolute.
An absolute path always contains the root element and the

...
/home/peter/statusReport
...

...
clarence/foo
...

the entry point for all file and directory operations. With

NIO.2 file and directory manipulation.
To obtain a Path object, obtain

Escaped backward slash

locate a file or a directory in a file system.

main(String[] args) {
Path p1 =

Run on a Windows machine. Note that except in a cmd shell, forward and backward slashes are legal.

to denote the current directory and “..” to denote the

/home/./clarence/foo
/home/peter/../clarence/foo

Path p = Paths.get("/home/peter/../clarence/foo");
Path normalizedPath = p.normalize();

/home/clarence/foo

by creating a subpath using the subpath method:
Path

Temp = 0
foo = 1
bar = 2

Include the element at index 2.

paths.
Example:


Passing an absolute path to the resolve method returns the

Path p1 = Paths.get("/home/clarence/foo");
p1.resolve("bar"); // Returns /home/clarence/foo/bar

Paths.get("foo").resolve("/home/clarence"); // Returns /home/clarence

to construct a path from one location in the file

Path p1 = Paths.get("peter");
Path p2 = Paths.get("clarence");

Path p1Top2 = p1.relativize(p2); // Result is ../clarence
Path p2Top1 = p2.relativize(p1); // Result is ../peter

do when a symbolic link is encountered, or
Provides an option

createSymbolicLink(Path, Path, FileAttribute)

createLink(Path, Path)

isSymbolicLink(Path)

readSymbolicLink(Path)

Creating a symbolic link

Creating a hard link

Detecting a symbolic link

Finding the target of a link

method would remove the redundant elements?
normalize
relativize
resolve
toAbsolutePath

sub = p.subPath (x, y);
What values for x and y

p3 = p1.resolve(p2).normalize();
System.out.println(p3);
What is the result?
Compiler error
IOException
D:\temp\foo\documents
D:\temp\bar\documents
D:\temp\foo\..\bar\documents

a File or Directory
Moving a File or Directory
Managing Metadata
Reading, Writing,

Random Access Files

Creating and Reading Directories

of a file or a directory location. Before you can

Optional argument

be accessed, the Files class provides the following boolean methods.
isReadable(Path)
isWritable(Path)
isExecutable(Path)
Note

one of the following methods:

Files.createFile (Path dir);

links. The Files class provides two methods:
delete(Path)
deleteIfExists(Path)
//...

Throws a NoSuchFileException,
DirectoryNotEmptyException, or
IOException

//...
Files.deleteIfExists(Path)
//...

No exception thrown

directory by using the copy(Path, Path, CopyOption...) method.
When directories are

//...
copy(Path, Path, CopyOption...)
//...

REPLACE_EXISTING COPY_ATTRIBUTES NOFOLLOW_LINKS

StandardCopyOption parameters

import static java.nio.file.StandardCopyOption.*;
//...
Files.copy(source, target, REPLACE_EXISTING, NOFOLLOW_LINKS);

be able to copy (or write) from a Stream to

directory by using the move(Path, Path, CopyOption...) method.
Moving a directory

//...
move(Path, Path, CopyOption...)
//...

REPLACE_EXISTING
ATOMIC_MOVE

StandardCopyOption parameters

import static java.nio.file.StandardCopyOption.*;
//...
Files.move(source, target, REPLACE_EXISTING);

iterate over all the entries in a directory.
Path dir

readAllLines method reads entire contents of the file in one

Path source = ...;
List lines;
Charset cs = Charset.defaultCharset();
lines = Files.readAllLines(file, cs);

Path target = ...;
Files.write(target, lines, cs, CREATE, TRUNCATE_EXISTING, WRITE);

StandardOpenOption enums.

while channel I/O reads a buffer at a time.
The ByteChannel

newByteChannel(Path, OpenOption...)
newByteChannel(Path, Set, FileAttribute...)

to a file’s contents.
To access a file randomly, open the

position()

position(long)

read(ByteBuffer)

write(ByteBuffer)

truncate(long)

file for reading.




The newBufferedWriter method writes to a file using

//...
BufferedReader reader = Files.newBufferedReader(file, charset);
line = reader.readLine();

//...
BufferedWriter writer = Files.newBufferedWriter(file, charset);
writer.write(s, 0, s.length());

a file, append to a file, or write to a

InputStream in = Files.newInputStream(file);
BufferedReader reader = new BufferedReader(new InputStreamReader(in));
line = reader.readLine();

import static java.nio.file.StandardOpenOption.*;
//...
Path logfile = ...;
String s = ...;
byte data[] = s.getBytes();
OutputStream out =
new BufferedOutputStream(file.newOutputStream(CREATE, APPEND);
out.write(data, 0, data.length);

or directory in a single call:

DosFileAttributes attrs =

= ...;
try { attrs =

POSIX file systems with their initial permissions set.

Path p

p2, StandardCopyOption.REPLACE_EXISTING);

If the peter2 directory does not exist, and the

source and target are not directories, how can you prevent

there are no exceptions, what is the result?
The contents of

file tree for recursive operations, such as copies and deletes.
walkFileTree

Files.walkFileTree(path, new PrintTree());
} catch (IOException e) {

directory. You could use a search tool, or a command,

syntax can be “glob” and “regex”.
The glob syntax is similar

// ... check for two arguments
Path root

private Path file;
private PathMatcher matcher;

usage information about a file system, such as the total,

for JDK 7 to provide forward compatibility with NIO.2.
Path path

Path interface to operate on file and directory paths
Use the

NIO.2, you must first create an instance of:
Path
Files
FileSystem
Channel

use to delete a file tree?
preVisitDirectory()
postVisitDirectory()
visitFile()
visitDirectory()

of a file tree (how many levels of directories), which