com.google.common.io
Class Files

java.lang.Object
  com.google.common.io.Files

@Beta
public final class Files
extends Object

Provides utility methods for working with files.

All method parameters must be non-null unless documented otherwise.

Since:

1.0

Author:

Chris Nokleberg

Method Summary

static void	append(CharSequence from, File to, Charset charset) Appends a character sequence (such as a string) to a file using the given character set.
static void	copy(File from, Charset charset, Appendable to) Copies all characters from a file to an appendable object, using the given character set.
static <W extends Appendable & Closeable> void	copy(File from, Charset charset, OutputSupplier<W> to) Copies all characters from a file to a Appendable & Closeable object supplied by a factory, using the given character set.
static void	copy(File from, File to) Copies all the bytes from one file to another.
static void	copy(File from, OutputStream to) Copies all bytes from a file to an output stream.
static void	copy(File from, OutputSupplier<? extends OutputStream> to) Copies all bytes from a file to an OutputStream supplied by a factory.
static void	copy(InputSupplier<? extends InputStream> from, File to) Copies to a file all bytes from an InputStream supplied by a factory.
static <R extends Readable & Closeable> void	copy(InputSupplier<R> from, File to, Charset charset) Copies to a file all characters from a Readable and Closeable object supplied by a factory, using the given character set.
static void	createParentDirs(File file) Creates any necessary but nonexistent parent directories of the specified file.
static File	createTempDir() Atomically creates a new directory somewhere beneath the system's temporary directory (as defined by the java.io.tmpdir system property), and returns its name.
static boolean	equal(File file1, File file2) Returns true if the files contains the same bytes.
static long	getChecksum(File file, Checksum checksum) Computes and returns the checksum value for a file.
static String	getFileExtension(String fileName) Returns the file extension for the given file name, or the empty string if the file has no extension.
static HashCode	hash(File file, HashFunction hashFunction) Computes the hash code of the file using hashFunction.
static MappedByteBuffer	map(File file) Fully maps a file read-only in to memory as per FileChannel.map(java.nio.channels.FileChannel.MapMode, long, long).
static MappedByteBuffer	map(File file, FileChannel.MapMode mode) Fully maps a file in to memory as per FileChannel.map(java.nio.channels.FileChannel.MapMode, long, long) using the requested FileChannel.MapMode.
static MappedByteBuffer	map(File file, FileChannel.MapMode mode, long size) Maps a file in to memory as per FileChannel.map(java.nio.channels.FileChannel.MapMode, long, long) using the requested FileChannel.MapMode.
static void	move(File from, File to) Moves the file from one path to another.
static InputSupplier<FileInputStream>	newInputStreamSupplier(File file) Returns a factory that will supply instances of FileInputStream that read from a file.
static OutputSupplier<FileOutputStream>	newOutputStreamSupplier(File file) Returns a factory that will supply instances of FileOutputStream that write to a file.
static OutputSupplier<FileOutputStream>	newOutputStreamSupplier(File file, boolean append) Returns a factory that will supply instances of FileOutputStream that write to or append to a file.
static BufferedReader	newReader(File file, Charset charset) Returns a buffered reader that reads from a file using the given character set.
static InputSupplier<InputStreamReader>	newReaderSupplier(File file, Charset charset) Returns a factory that will supply instances of InputStreamReader that read a file using the given character set.
static BufferedWriter	newWriter(File file, Charset charset) Returns a buffered writer that writes to a file using the given character set.
static OutputSupplier<OutputStreamWriter>	newWriterSupplier(File file, Charset charset) Returns a factory that will supply instances of OutputStreamWriter that write to a file using the given character set.
static OutputSupplier<OutputStreamWriter>	newWriterSupplier(File file, Charset charset, boolean append) Returns a factory that will supply instances of OutputStreamWriter that write to or append to a file using the given character set.
static <T> T	readBytes(File file, ByteProcessor<T> processor) Process the bytes of a file.
static String	readFirstLine(File file, Charset charset) Reads the first line from a file.
static List<String>	readLines(File file, Charset charset) Reads all of the lines from a file.
static <T> T	readLines(File file, Charset charset, LineProcessor<T> callback) Streams lines from a File, stopping when our callback returns false, or we have read all of the lines.
static String	simplifyPath(String pathname) Returns the lexically cleaned form of the path name, usually (but not always) equivalent to the original.
static byte[]	toByteArray(File file) Reads all bytes from a file into a byte array.
static String	toString(File file, Charset charset) Reads all characters from a file into a String, using the given character set.
static void	touch(File file) Creates an empty file or updates the last updated timestamp on the same as the unix command of the same name.
static void	write(byte[] from, File to) Overwrites a file with the contents of a byte array.
static void	write(CharSequence from, File to, Charset charset) Writes a character sequence (such as a string) to a file using the given character set.

Methods inherited from class java.lang.Object

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

Method Detail

newReader

public static BufferedReader newReader(File file,
                                       Charset charset)
                                throws FileNotFoundException

Returns a buffered reader that reads from a file using the given character set.

Parameters:

file - the file to read from

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

Returns:

the buffered reader

Throws:

FileNotFoundException

newWriter

public static BufferedWriter newWriter(File file,
                                       Charset charset)
                                throws FileNotFoundException

Returns a buffered writer that writes to a file using the given character set.

Parameters:

file - the file to write to

charset - the charset used to encode the output stream; see Charsets for helpful predefined constants

Returns:

the buffered writer

Throws:

FileNotFoundException

newInputStreamSupplier

public static InputSupplier<FileInputStream> newInputStreamSupplier(File file)

Returns a factory that will supply instances of FileInputStream that read from a file.

Parameters:

file - the file to read from

Returns:

the factory

newOutputStreamSupplier

public static OutputSupplier<FileOutputStream> newOutputStreamSupplier(File file)

Returns a factory that will supply instances of FileOutputStream that write to a file.

Parameters:

file - the file to write to

Returns:

the factory

newOutputStreamSupplier

public static OutputSupplier<FileOutputStream> newOutputStreamSupplier(File file,
                                                                       boolean append)

Returns a factory that will supply instances of FileOutputStream that write to or append to a file.

Parameters:

file - the file to write to

append - if true, the encoded characters will be appended to the file; otherwise the file is overwritten

Returns:

the factory

newReaderSupplier

public static InputSupplier<InputStreamReader> newReaderSupplier(File file,
                                                                 Charset charset)

Returns a factory that will supply instances of InputStreamReader that read a file using the given character set.

Parameters:

file - the file to read from

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

Returns:

the factory

newWriterSupplier

public static OutputSupplier<OutputStreamWriter> newWriterSupplier(File file,
                                                                   Charset charset)

Returns a factory that will supply instances of OutputStreamWriter that write to a file using the given character set.

Parameters:

file - the file to write to

charset - the charset used to encode the output stream; see Charsets for helpful predefined constants

Returns:

the factory

newWriterSupplier

public static OutputSupplier<OutputStreamWriter> newWriterSupplier(File file,
                                                                   Charset charset,
                                                                   boolean append)

Returns a factory that will supply instances of OutputStreamWriter that write to or append to a file using the given character set.

Parameters:

file - the file to write to

charset - the charset used to encode the output stream; see Charsets for helpful predefined constants

append - if true, the encoded characters will be appended to the file; otherwise the file is overwritten

Returns:

the factory

toByteArray

public static byte[] toByteArray(File file)
                          throws IOException

Reads all bytes from a file into a byte array.

Parameters:

file - the file to read from

Returns:

a byte array containing all the bytes from file

Throws:

IllegalArgumentException - if the file is bigger than the largest possible byte array (2^31 - 1)

IOException - if an I/O error occurs

toString

public static String toString(File file,
                              Charset charset)
                       throws IOException

Reads all characters from a file into a String, using the given character set.

Parameters:

file - the file to read from

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

Returns:

a string containing all the characters from the file

Throws:

IOException - if an I/O error occurs

copy

public static void copy(InputSupplier<? extends InputStream> from,
                        File to)
                 throws IOException

Copies to a file all bytes from an InputStream supplied by a factory.

Parameters:

from - the input factory

to - the destination file

Throws:

IOException - if an I/O error occurs

write

public static void write(byte[] from,
                         File to)
                  throws IOException

Overwrites a file with the contents of a byte array.

Parameters:

from - the bytes to write

to - the destination file

Throws:

IOException - if an I/O error occurs

copy

public static void copy(File from,
                        OutputSupplier<? extends OutputStream> to)
                 throws IOException

Copies all bytes from a file to an OutputStream supplied by a factory.

Parameters:

from - the source file

to - the output factory

Throws:

IOException - if an I/O error occurs

copy

public static void copy(File from,
                        OutputStream to)
                 throws IOException

Copies all bytes from a file to an output stream.

Parameters:

from - the source file

to - the output stream

Throws:

IOException - if an I/O error occurs

copy

public static void copy(File from,
                        File to)
                 throws IOException

Copies all the bytes from one file to another. .

Parameters:

from - the source file

to - the destination file

Throws:

IOException - if an I/O error occurs

IllegalArgumentException - if from.equals(to)

copy

public static <R extends Readable & Closeable> void copy(InputSupplier<R> from,
                                                        File to,
                                                        Charset charset)
                 throws IOException

Copies to a file all characters from a Readable and Closeable object supplied by a factory, using the given character set.

Parameters:

from - the readable supplier

to - the destination file

charset - the charset used to encode the output stream; see Charsets for helpful predefined constants

Throws:

IOException - if an I/O error occurs

write

public static void write(CharSequence from,
                         File to,
                         Charset charset)
                  throws IOException

Writes a character sequence (such as a string) to a file using the given character set.

Parameters:

from - the character sequence to write

to - the destination file

charset - the charset used to encode the output stream; see Charsets for helpful predefined constants

Throws:

IOException - if an I/O error occurs

append

public static void append(CharSequence from,
                          File to,
                          Charset charset)
                   throws IOException

Appends a character sequence (such as a string) to a file using the given character set.

Parameters:

from - the character sequence to append

to - the destination file

charset - the charset used to encode the output stream; see Charsets for helpful predefined constants

Throws:

IOException - if an I/O error occurs

copy

public static <W extends Appendable & Closeable> void copy(File from,
                                                          Charset charset,
                                                          OutputSupplier<W> to)
                 throws IOException

Copies all characters from a file to a Appendable & Closeable object supplied by a factory, using the given character set.

Parameters:

from - the source file

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

to - the appendable supplier

Throws:

IOException - if an I/O error occurs

copy

public static void copy(File from,
                        Charset charset,
                        Appendable to)
                 throws IOException

Copies all characters from a file to an appendable object, using the given character set.

Parameters:

from - the source file

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

to - the appendable object

Throws:

IOException - if an I/O error occurs

equal

public static boolean equal(File file1,
                            File file2)
                     throws IOException

Returns true if the files contains the same bytes.

Throws:

IOException - if an I/O error occurs

createTempDir

public static File createTempDir()

Atomically creates a new directory somewhere beneath the system's temporary directory (as defined by the java.io.tmpdir system property), and returns its name.

Use this method instead of File.createTempFile(String, String) when you wish to create a directory, not a regular file. A common pitfall is to call createTempFile, delete the file and create a directory in its place, but this leads a race condition which can be exploited to create security vulnerabilities, especially when executable files are to be written into the directory.

This method assumes that the temporary volume is writable, has free inodes and free blocks, and that it will not be called thousands of times per second.

Returns:

the newly-created directory

Throws:

IllegalStateException - if the directory could not be created

touch

public static void touch(File file)
                  throws IOException

Creates an empty file or updates the last updated timestamp on the same as the unix command of the same name.

Parameters:

file - the file to create or update

Throws:

IOException - if an I/O error occurs

createParentDirs

public static void createParentDirs(File file)
                             throws IOException

Creates any necessary but nonexistent parent directories of the specified file. Note that if this operation fails it may have succeeded in creating some (but not all) of the necessary parent directories.

Throws:

IOException - if an I/O error occurs, or if any necessary but nonexistent parent directories of the specified file could not be created.

Since:

4.0

move

public static void move(File from,
                        File to)
                 throws IOException

Moves the file from one path to another. This method can rename a file or move it to a different directory, like the Unix mv command.

Parameters:

from - the source file

to - the destination file

Throws:

IOException - if an I/O error occurs

IllegalArgumentException - if from.equals(to)

readFirstLine

public static String readFirstLine(File file,
                                   Charset charset)
                            throws IOException

Reads the first line from a file. The line does not include line-termination characters, but does include other leading and trailing whitespace.

Parameters:

file - the file to read from

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

Returns:

the first line, or null if the file is empty

Throws:

IOException - if an I/O error occurs

readLines

public static List<String> readLines(File file,
                                     Charset charset)
                              throws IOException

Reads all of the lines from a file. The lines do not include line-termination characters, but do include other leading and trailing whitespace.

Parameters:

file - the file to read from

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

Returns:

a mutable List containing all the lines

Throws:

IOException - if an I/O error occurs

readLines

public static <T> T readLines(File file,
                              Charset charset,
                              LineProcessor<T> callback)
                   throws IOException

Streams lines from a File, stopping when our callback returns false, or we have read all of the lines.

Parameters:

file - the file to read from

charset - the charset used to decode the input stream; see Charsets for helpful predefined constants

callback - the LineProcessor to use to handle the lines

Returns:

the output of processing the lines

Throws:

IOException - if an I/O error occurs

readBytes

public static <T> T readBytes(File file,
                              ByteProcessor<T> processor)
                   throws IOException

Process the bytes of a file.

(If this seems too complicated, maybe you're looking for toByteArray(java.io.File).)

Parameters:

file - the file to read

processor - the object to which the bytes of the file are passed.

Returns:

the result of the byte processor

Throws:

IOException - if an I/O error occurs

getChecksum

public static long getChecksum(File file,
                               Checksum checksum)
                        throws IOException

Computes and returns the checksum value for a file. The checksum object is reset when this method returns successfully.

Parameters:

file - the file to read

checksum - the checksum object

Returns:

the result of Checksum.getValue() after updating the checksum object with all of the bytes in the file

Throws:

IOException - if an I/O error occurs

hash

public static HashCode hash(File file,
                            HashFunction hashFunction)
                     throws IOException

Computes the hash code of the file using hashFunction.

Parameters:

file - the file to read

hashFunction - the hash function to use to hash the data

Returns:

the HashCode of all of the bytes in the file

Throws:

IOException - if an I/O error occurs

Since:

12.0

map

public static MappedByteBuffer map(File file)
                            throws IOException

Fully maps a file read-only in to memory as per FileChannel.map(java.nio.channels.FileChannel.MapMode, long, long).

Files are mapped from offset 0 to its length.

This only works for files <= Integer.MAX_VALUE bytes.

Parameters:

file - the file to map

Returns:

a read-only buffer reflecting file

Throws:

FileNotFoundException - if the file does not exist

IOException - if an I/O error occurs

Since:

2.0

See Also:

FileChannel.map(MapMode, long, long)

map

public static MappedByteBuffer map(File file,
                                   FileChannel.MapMode mode)
                            throws IOException

Fully maps a file in to memory as per FileChannel.map(java.nio.channels.FileChannel.MapMode, long, long) using the requested FileChannel.MapMode.

Files are mapped from offset 0 to its length.

This only works for files <= Integer.MAX_VALUE bytes.

Parameters:

file - the file to map

mode - the mode to use when mapping file

Returns:

a buffer reflecting file

Throws:

FileNotFoundException - if the file does not exist

IOException - if an I/O error occurs

Since:

2.0

See Also:

FileChannel.map(MapMode, long, long)

map

public static MappedByteBuffer map(File file,
                                   FileChannel.MapMode mode,
                                   long size)
                            throws FileNotFoundException,
                                   IOException

Maps a file in to memory as per FileChannel.map(java.nio.channels.FileChannel.MapMode, long, long) using the requested FileChannel.MapMode.

Files are mapped from offset 0 to size.

If the mode is FileChannel.MapMode.READ_WRITE and the file does not exist, it will be created with the requested size. Thus this method is useful for creating memory mapped files which do not yet exist.

This only works for files <= Integer.MAX_VALUE bytes.

Parameters:

file - the file to map

mode - the mode to use when mapping file

Returns:

a buffer reflecting file

Throws:

IOException - if an I/O error occurs

FileNotFoundException

Since:

2.0

See Also:

FileChannel.map(MapMode, long, long)

simplifyPath

public static String simplifyPath(String pathname)

Returns the lexically cleaned form of the path name, usually (but not always) equivalent to the original. The following heuristics are used:

• empty string becomes .
• . stays as .
• fold out ./
• fold out ../ when possible
• collapse multiple slashes
• delete trailing slashes (unless the path is just "/")

These heuristics do not always match the behavior of the filesystem. In particular, consider the path a/../b, which simplifyPath will change to b. If a is a symlink to x, a/../b may refer to a sibling of x, rather than the sibling of a referred to by b.

Since:

11.0

getFileExtension

public static String getFileExtension(String fileName)

Returns the file extension for the given file name, or the empty string if the file has no extension. The result does not include the '.'.

Since:

11.0