Java system path separator

The conversion of a pathname string to or from an abstract pathname is inherently system-dependent. When an abstract pathname is converted into a pathname string, each name is separated from the next by a single copy of the default separator character. The default name-separator character is defined by the system property file.separator , and is made available in the public static fields separator and separatorChar of this class. When a pathname string is converted into an abstract pathname, the names within it may be separated by the default name-separator character or by any other name-separator character that is supported by the underlying system.

A pathname, whether abstract or in string form, may be either absolute or relative. An absolute pathname is complete in that no other information is required in order to locate the file that it denotes. A relative pathname, in contrast, must be interpreted in terms of information taken from some other pathname. By default the classes in the java.io package always resolve relative pathnames against the current user directory. This directory is named by the system property user.dir , and is typically the directory in which the Java virtual machine was invoked.

The parent of an abstract pathname may be obtained by invoking the getParent() method of this class and consists of the pathname’s prefix and each name in the pathname’s name sequence except for the last. Each directory’s absolute pathname is an ancestor of any File object with an absolute abstract pathname which begins with the directory’s absolute pathname. For example, the directory denoted by the abstract pathname «/usr» is an ancestor of the directory denoted by the pathname «/usr/local/bin» .

For UNIX platforms, the prefix of an absolute pathname is always «/» . Relative pathnames have no prefix. The abstract pathname denoting the root directory has the prefix «/» and an empty name sequence.
For Microsoft Windows platforms, the prefix of a pathname that contains a drive specifier consists of the drive letter followed by «:» and possibly followed by «\\» if the pathname is absolute. The prefix of a UNC pathname is «\\\\» ; the hostname and the share name are the first two names in the name sequence. A relative pathname that does not specify a drive has no prefix.

Instances of this class may or may not denote an actual file-system object such as a file or a directory. If it does denote such an object then that object resides in a partition. A partition is an operating system-specific portion of storage for a file system. A single storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may contain multiple partitions. The object, if any, will reside on the partition named by some ancestor of the absolute form of this pathname.

A file system may implement restrictions to certain operations on the actual file-system object, such as reading, writing, and executing. These restrictions are collectively known as access permissions. The file system may have multiple sets of access permissions on a single object. For example, one set may apply to the object’s owner, and another may apply to all other users. The access permissions on an object may cause some methods in this class to fail.

Instances of the File class are immutable; that is, once created, the abstract pathname represented by a File object will never change.

Interoperability with java.nio.file package

The java.nio.file package defines interfaces and classes for the Java virtual machine to access files, file attributes, and file systems. This API may be used to overcome many of the limitations of the java.io.File class. The toPath method may be used to obtain a Path that uses the abstract path represented by a File object to locate a file. The resulting Path may be used with the Files class to provide more efficient and extensive access to additional file operations, file attributes, and I/O exceptions to help diagnose errors when an operation on a file fails.

Читайте также: Java arrays and objects

Источник

Class File

For UNIX platforms, the prefix of an absolute pathname is always «/» . Relative pathnames have no prefix. The abstract pathname denoting the root directory has the prefix «/» and an empty name sequence.
For Microsoft Windows platforms, the prefix of a pathname that contains a drive specifier consists of the drive letter followed by «:» and possibly followed by «\\» if the pathname is absolute. The prefix of a UNC pathname is «\\\\» ; the hostname and the share name are the first two names in the name sequence. A relative pathname that does not specify a drive has no prefix.

Instances of the File class are immutable; that is, once created, the abstract pathname represented by a File object will never change.

Interoperability with java.nio.file package

Источник

Get file path separator in Java

In this article, we will present how to get a file path separator in Java. A file separator is platform-dependent what means in Unix we will have a different separator than in Windows OS. That’s why it is important to use Java-built methods to retrieve it when we are working with files.

We can get file path separator in three ways:

using System.getProperty(«file.separator») ,
with FileSystems.getDefault().getSeparator() method from the latest Java NIO,
using File.separator from Java IO API.

2. Get a file path separator using a system property

In system properties JVM holds information about the configuration of the current working environment such as a current version of Java runtime («java.version»), current user («user.name»), and also the character used to separate elements of the file pathname («file.separator»).

Let’s check the example code that makes use of that system properties to get file path separator:

package com.frontbackend.java.io.separator; public class FilePathSeparatorFromSystemProperty < public static void main(String[] args) < String pathSeparator = System.getProperty("file.separator"); System.out.println(pathSeparator); // in Unix /, in Windows \ >>

Note that System.getProperties() can be overridden using System.setProperty(String key, String value) or with command line parameters -Dfile.separator=/ , so we could not rely on this parameter in 100%.

3. Retrieve path separator with FileSystems.getDefault().getSeparator() method

Another method to get a file path separator comes with Java NIO API. This API provides a dedicated method called on FilesSystems class to get the name of the separator used to separate names in a path string.

The following example shows how to use a platform-independent method from Java NIO to get a file path separator:

package com.frontbackend.java.io.separator; import java.nio.file.FileSystems; public class FilePathSeparatorUsingJavaNIO < public static void main(String[] args) < String pathSeparator = FileSystems.getDefault() .getSeparator(); System.out.println(pathSeparator); // in Unix / , in Windows \ >>

4. File path separator using Java IO File.separator

In older Java IO API there is also a property that holds a file path separator File.separator :

package com.frontbackend.java.io.separator; import java.io.File; public class FilePathSeparatorUsingJavaIOAPI < public static void main(String[] args) < String pathSeparator = File.separator; System.out.println(pathSeparator); // Unix / , Windows \ >>

We recommend using the FileSystems.getDefault().getSeparator() method that was provided in Java NIO.

5. Conclusion

This article covered methods used to get a file path separator in Java. It is important to use methods available in Java IO or NIO API, instead of hardcoded values. This will prevent unexpected exceptions and errors when working with files in Java applications.

As always code snippets used in this article are available under the GitHub repository.

Источник