Class FileOutputStream

All Implemented Interfaces:
Closeable, Flushable, AutoCloseable 
public class FileOutputStream
extends OutputStream

A file output stream is an output stream for writing data to a File or to a FileDescriptor. Whether or not a file is available or may be created depends upon the underlying platform. Some platforms, in particular, allow a file to be opened for writing by only one FileOutputStream (or other file-writing object) at a time. In such situations the constructors in this class will fail if the file involved is already open.

FileOutputStream is meant for writing streams of raw bytes such as image data. For writing streams of characters, consider using FileWriter.

API Note:
To release resources used by this stream close() should be called directly or by try-with-resources. Subclasses are responsible for the cleanup of resources acquired by the subclass. Subclasses that override finalize() in order to perform cleanup should be modified to use alternative cleanup mechanisms such as Cleaner and remove the overriding finalize method.
Implementation Requirements:
If this FileOutputStream has been subclassed and the close() method has been overridden, the close() method will be called when the FileInputStream is unreachable. Otherwise, it is implementation specific how the resource cleanup described in close() is performed.
Since:
1.0
See Also:
File, FileDescriptor, FileInputStream, Files.newOutputStream(java.nio.file.Path, java.nio.file.OpenOption...)

Constructors

Constructor Description
FileOutputStream​(File file)

Creates a file output stream to write to the file represented by the specified File object.
FileOutputStream​(FileDescriptor fdObj)

Creates a file output stream to write to the specified file descriptor, which represents an existing connection to an actual file in the file system.
FileOutputStream​(File file, boolean append)

Creates a file output stream to write to the file represented by the specified File object.
FileOutputStream​(String name)

Creates a file output stream to write to the file with the specified name.
FileOutputStream​(String name, boolean append)

Creates a file output stream to write to the file with the specified name.

Methods

Modifier and Type Method Description
void close()

Closes this file output stream and releases any system resources associated with this stream.
protected void finalize()

Deprecated, for removal: This API element is subject to removal in a future version.

The finalize method has been deprecated and will be removed.
FileChannel getChannel()

Returns the unique FileChannel object associated with this file output stream.
FileDescriptor getFD()

Returns the file descriptor associated with this stream.
void write​(byte[] b)

Writes b.length bytes from the specified byte array to this file output stream.
void write​(byte[] b, int off, int len)

Writes len bytes from the specified byte array starting at offset off to this file output stream.
void write​(int b)

Writes the specified byte to this file output stream.

Methods declared in class java.io.OutputStream

flush, nullOutputStream

Methods declared in class java.lang.Object

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

Constructors

FileOutputStream

public FileOutputStream(String name)
                 throws FileNotFoundException

Creates a file output stream to write to the file with the specified name. A new FileDescriptor object is created to represent this file connection.

First, if there is a security manager, its checkWrite method is called with name as its argument.

If the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason then a FileNotFoundException is thrown.

Implementation Requirements:
Invoking this constructor with the parameter name is equivalent to invoking new FileOutputStream(name, false).
Parameters:
name - the system-dependent filename
Throws:
FileNotFoundException - if the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason
SecurityException - if a security manager exists and its checkWrite method denies write access to the file.
See Also:
SecurityManager.checkWrite(java.lang.String)

FileOutputStream

public FileOutputStream(String name,
                        boolean append)
                 throws FileNotFoundException

Creates a file output stream to write to the file with the specified name. If the second argument is true, then bytes will be written to the end of the file rather than the beginning. A new FileDescriptor object is created to represent this file connection.

First, if there is a security manager, its checkWrite method is called with name as its argument.

If the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason then a FileNotFoundException is thrown.

Parameters:
name - the system-dependent file name
append - if true, then bytes will be written to the end of the file rather than the beginning
Throws:
FileNotFoundException - if the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason.
SecurityException - if a security manager exists and its checkWrite method denies write access to the file.
Since:
1.1
See Also:
SecurityManager.checkWrite(java.lang.String)

FileOutputStream

public FileOutputStream(File file)
                 throws FileNotFoundException

Creates a file output stream to write to the file represented by the specified File object. A new FileDescriptor object is created to represent this file connection.

First, if there is a security manager, its checkWrite method is called with the path represented by the file argument as its argument.

If the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason then a FileNotFoundException is thrown.

Parameters:
file - the file to be opened for writing.
Throws:
FileNotFoundException - if the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason
SecurityException - if a security manager exists and its checkWrite method denies write access to the file.
See Also:
File.getPath(), SecurityException, SecurityManager.checkWrite(java.lang.String)

FileOutputStream

public FileOutputStream(File file,
                        boolean append)
                 throws FileNotFoundException

Creates a file output stream to write to the file represented by the specified File object. If the second argument is true, then bytes will be written to the end of the file rather than the beginning. A new FileDescriptor object is created to represent this file connection.

First, if there is a security manager, its checkWrite method is called with the path represented by the file argument as its argument.

If the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason then a FileNotFoundException is thrown.

Parameters:
file - the file to be opened for writing.
append - if true, then bytes will be written to the end of the file rather than the beginning
Throws:
FileNotFoundException - if the file exists but is a directory rather than a regular file, does not exist but cannot be created, or cannot be opened for any other reason
SecurityException - if a security manager exists and its checkWrite method denies write access to the file.
Since:
1.4
See Also:
File.getPath(), SecurityException, SecurityManager.checkWrite(java.lang.String)

FileOutputStream

public FileOutputStream(FileDescriptor fdObj)

Creates a file output stream to write to the specified file descriptor, which represents an existing connection to an actual file in the file system.

First, if there is a security manager, its checkWrite method is called with the file descriptor fdObj argument as its argument.

If fdObj is null then a NullPointerException is thrown.

This constructor does not throw an exception if fdObj is invalid. However, if the methods are invoked on the resulting stream to attempt I/O on the stream, an IOException is thrown.

Parameters:
fdObj - the file descriptor to be opened for writing
Throws:
SecurityException - if a security manager exists and its checkWrite method denies write access to the file descriptor
See Also:
SecurityManager.checkWrite(java.io.FileDescriptor)

Methods

write

public void write(int b)
           throws IOException

Writes the specified byte to this file output stream. Implements the write method of OutputStream.

Specified by:
write in class OutputStream
Parameters:
b - the byte to be written.
Throws:
IOException - if an I/O error occurs.

write

public void write(byte[] b)
           throws IOException

Writes b.length bytes from the specified byte array to this file output stream.

Overrides:
write in class OutputStream
Parameters:
b - the data.
Throws:
IOException - if an I/O error occurs.
See Also:
OutputStream.write(byte[], int, int)

write

public void write(byte[] b,
                  int off,
                  int len)
           throws IOException

Writes len bytes from the specified byte array starting at offset off to this file output stream.

Overrides:
write in class OutputStream
Parameters:
b - the data.
off - the start offset in the data.
len - the number of bytes to write.
Throws:
IOException - if an I/O error occurs.

close

public void close()
           throws IOException

Closes this file output stream and releases any system resources associated with this stream. This file output stream may no longer be used for writing bytes.

If this stream has an associated channel then the channel is closed as well.

Specified by:
close in interface AutoCloseable
Specified by:
close in interface Closeable
Overrides:
close in class OutputStream
API Note:
Overriding close() to perform cleanup actions is reliable only when called directly or when called by try-with-resources. Do not depend on finalization to invoke close; finalization is not reliable and is deprecated. If cleanup of native resources is needed, other mechanisms such as Cleaner should be used.
Throws:
IOException - if an I/O error occurs.

getFD

public final FileDescriptor getFD()
                           throws IOException

Returns the file descriptor associated with this stream.

Returns:
the FileDescriptor object that represents the connection to the file in the file system being used by this FileOutputStream object.
Throws:
IOException - if an I/O error occurs.
See Also:
FileDescriptor

getChannel

public FileChannel getChannel()

Returns the unique FileChannel object associated with this file output stream.

The initial position of the returned channel will be equal to the number of bytes written to the file so far unless this stream is in append mode, in which case it will be equal to the size of the file. Writing bytes to this stream will increment the channel's position accordingly. Changing the channel's position, either explicitly or by writing, will change this stream's file position.

Returns:
the file channel associated with this file output stream
Since:
1.4

finalize

@Deprecated(since="9",
            forRemoval=true)
protected void finalize()
                 throws IOException
Deprecated, for removal: This API element is subject to removal in a future version.
The finalize method has been deprecated and will be removed. Subclasses that override finalize in order to perform cleanup should be modified to use alternative cleanup mechanisms and to remove the overriding finalize method. When overriding the finalize method, its implementation must explicitly ensure that super.finalize() is invoked as described in Object.finalize(). See the specification for Object.finalize() for further information about migration options.

Cleans up the connection to the file, and ensures that the close() method of this file output stream is called when there are no more references to this stream. The finalize() method does not call close() directly.

Overrides:
finalize in class Object
API Note:
To release resources used by this stream close() should be called directly or by try-with-resources.
Implementation Requirements:
If this FileOutputStream has been subclassed and the close() method has been overridden, the close() method will be called when the FileOutputStream is unreachable. Otherwise, it is implementation specific how the resource cleanup described in close() is performed.
Throws:
IOException - if an I/O error occurs.
See Also:
FileInputStream.close()

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/io/FileOutputStream.html