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java.nio.file
Class Files

java.lang.Object
  java.nio.file.Files

public final class Files
extends Object

This class consists exclusively of static methods that operate on files or directories.

Since:

1.7

Method Summary

Modifier and Type	Method and Description
static void	createDirectories(Path dir, FileAttribute<?>... attrs) Creates a directory by creating all nonexistent parent directories first.
static String	probeContentType(FileRef file) Probes the content type of a file.
static void	walkFileTree(Path start, FileVisitor<? super Path> visitor) Walks a file tree.
static void	walkFileTree(Path start, Set<FileVisitOption> options, int maxDepth, FileVisitor<? super Path> visitor) Walks a file tree.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

probeContentType

public static String probeContentType(FileRef file)
                               throws IOException

Probes the content type of a file.

This method uses the installed FileTypeDetector implementations to probe the given file to determine its content type. Each file type detector's probeContentType is invoked, in turn, to probe the file type. If the file is recognized then the content type is returned. If the file is not recognized by any of the installed file type detectors then a system-default file type detector is invoked to guess the content type.

A given invocation of the Java virtual machine maintains a system-wide list of file type detectors. Installed file type detectors are loaded using the service-provider loading facility defined by the ServiceLoader class. Installed file type detectors are loaded using the system class loader. If the system class loader cannot be found then the extension class loader is used; If the extension class loader cannot be found then the bootstrap class loader is used. File type detectors are typically installed by placing them in a JAR file on the application class path or in the extension directory, the JAR file contains a provider-configuration file named java.nio.file.spi.FileTypeDetector in the resource directory META-INF/services, and the file lists one or more fully-qualified names of concrete subclass of FileTypeDetector that have a zero argument constructor. If the process of locating or instantiating the installed file type detectors fails then an unspecified error is thrown. The ordering that installed providers are located is implementation specific.

The return value of this method is the string form of the value of a Multipurpose Internet Mail Extension (MIME) content type as defined by RFC 2045: Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies. The string is guaranteed to be parsable according to the grammar in the RFC.

Parameters:

file - The file reference

Returns:

The content type of the file, or null if the content type cannot be determined

Throws:

IOException - If an I/O error occurs

SecurityException - If a security manager is installed and it denies an unspecified permission required by a file type detector implementation.

walkFileTree

public static void walkFileTree(Path start,
                                Set<FileVisitOption> options,
                                int maxDepth,
                                FileVisitor<? super Path> visitor)
                         throws IOException

Walks a file tree.

This method walks a file tree rooted at a given starting file. The file tree traversal is depth-first with the given FileVisitor invoked for each file encountered. File tree traversal completes when all accessible files in the tree have been visited, or a visit method returns a result of TERMINATE. Where a visit method terminates due an IOException, an uncaught error, or runtime exception, then the traversal is terminated and the error or exception is propagated to the caller of this method.

For each file encountered this method attempts to gets its BasicFileAttributes. If the file is not a directory then the visitFile method is invoked with the file attributes. If the file attributes cannot be read, due to an I/O exception, then the visitFileFailed method is invoked with the I/O exception.

Where the file is a directory, and the directory could not be opened, then the visitFileFailed method is invoked with the I/O exception, after which, the file tree walk continues, by default, at the next sibling of the directory.

Where the directory is opened successfully, then the entries in the directory, and their descendants are visited. When all entries have been visited, or an I/O error occurs during iteration of the directory, then the directory is closed and the visitor's postVisitDirectory method is invoked. The file tree walk then continues, by default, at the next sibling of the directory.

By default, symbolic links are not automatically followed by this method. If the options parameter contains the FOLLOW_LINKS option then symbolic links are followed. When following links, and the attributes of the target cannot be read, then this method attempts to get the BasicFileAttributes of the link. If they can be read then the visitFile method is invoked with the attributes of the link (otherwise the visitFileFailed method is invoked as specified above).

If the options parameter contains the FOLLOW_LINKS option then this method keeps track of directories visited so that cycles can be detected. A cycle arises when there is an entry in a directory that is an ancestor of the directory. Cycle detection is done by recording the file-key of directories, or if file keys are not available, by invoking the isSameFile method to test if a directory is the same file as an ancestor. When a cycle is detected it is treated as an I/O error, and the visitFileFailed method is invoked with an instance of FileSystemLoopException.

The maxDepth parameter is the maximum number of levels of directories to visit. A value of 0 means that only the starting file is visited, unless denied by the security manager. A value of MAX_VALUE may be used to indicate that all levels should be visited. The visitFile method is invoked for all files, including directories, encountered at maxDepth, unless the basic file attributes cannot be read, in which case the visitFileFailed method is invoked.

If a visitor returns a result of null then NullPointerException is thrown.

When a security manager is installed and it denies access to a file (or directory), then it is ignored and the visitor is not invoked for that file (or directory).

Parameters:

start - The starting file

options - Options to configure the traversal

maxDepth - The maximum number of directory levels to visit

visitor - The file visitor to invoke for each file

Throws:

IllegalArgumentException - If the maxDepth parameter is negative

SecurityException - If the security manager denies access to the starting file. In the case of the default provider, the checkRead method is invoked to check read access to the directory.

IOException - If an I/O error is thrown by a visitor method

walkFileTree

public static void walkFileTree(Path start,
                                FileVisitor<? super Path> visitor)
                         throws IOException

Walks a file tree.

This method works as if invoking it were equivalent to evaluating the expression:

 walkFileTree(start, EnumSet.noneOf(FileVisitOption.class), Integer.MAX_VALUE, visitor)
 

Parameters:

start - The starting file

visitor - The file visitor to invoke for each file

Throws:

SecurityException - If the security manager denies access to the starting file. In the case of the default provider, the checkRead method is invoked to check read access to the directory.

IOException - If an I/O error is thrown by a visitor method

createDirectories

public static void createDirectories(Path dir,
                                     FileAttribute<?>... attrs)
                              throws IOException

Creates a directory by creating all nonexistent parent directories first.

The attrs parameter is an optional array of file-attributes to set atomically when creating the nonexistent directories. Each file attribute is identified by its name. If more than one attribute of the same name is included in the array then all but the last occurrence is ignored.

If this method fails, then it may do so after creating some, but not all, of the parent directories.

Parameters:

dir - the directory to create

attrs - an optional list of file attributes to set atomically when creating the directory

Throws:

UnsupportedOperationException - if the array contains an attribute that cannot be set atomically when creating the directory

FileAlreadyExistsException - if dir exists but is not a directory (optional specific exception)

IOException - if an I/O error occurs

SecurityException - in the case of the default provider, and a security manager is installed, the checkWrite method is invoked prior to attempting to create a directory and its checkRead is invoked for each parent directory that is checked. If dir is not an absolute path then its toAbsolutePath may need to be invoked to get its absolute path. This may invoke the security manager's checkPropertyAccess method to check access to the system property user.dir