Class FileInputStream

All Implemented Interfaces:
Closeable, AutoCloseable 
public class FileInputStream
extends InputStream

A FileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment.

FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader.

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 FileInputStream 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, FileOutputStream, Files.newInputStream(java.nio.file.Path, java.nio.file.OpenOption...)

Constructors

Constructor Description
FileInputStream​(File file)

Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system.
FileInputStream​(FileDescriptor fdObj)

Creates a FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system.
FileInputStream​(String name)

Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system.

Methods

Modifier and Type Method Description
int available()

Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream.
void close()

Closes this file input stream and releases any system resources associated with the 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 input stream.
FileDescriptor getFD()

Returns the FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream.
int read()

Reads a byte of data from this input stream.
int read​(byte[] b)

Reads up to b.length bytes of data from this input stream into an array of bytes.
int read​(byte[] b, int off, int len)

Reads up to len bytes of data from this input stream into an array of bytes.
long skip​(long n)

Skips over and discards n bytes of data from the input stream.

Methods declared in class java.io.InputStream

mark, markSupported, nullInputStream, readAllBytes, readNBytes, readNBytes, reset, transferTo

Methods declared in class java.lang.Object

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

Constructors

FileInputStream

public FileInputStream(String name)
                throws FileNotFoundException

Creates a FileInputStream by opening a connection to an actual file, the file named by the path name name in the file system. A new FileDescriptor object is created to represent this file connection.

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

If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown.

Parameters:
name - the system-dependent file name.
Throws:
FileNotFoundException - if the file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading.
SecurityException - if a security manager exists and its checkRead method denies read access to the file.
See Also:
SecurityManager.checkRead(java.lang.String)

FileInputStream

public FileInputStream(File file)
                throws FileNotFoundException

Creates a FileInputStream by opening a connection to an actual file, the file named by the File object file in the file system. A new FileDescriptor object is created to represent this file connection.

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

If the named file does not exist, is a directory rather than a regular file, or for some other reason cannot be opened for reading then a FileNotFoundException is thrown.

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

FileInputStream

public FileInputStream(FileDescriptor fdObj)

Creates a FileInputStream by using the file descriptor fdObj, which represents an existing connection to an actual file in the file system.

If there is a security manager, its checkRead method is called with the file descriptor fdObj as its argument to see if it's ok to read the file descriptor. If read access is denied to the file descriptor a SecurityException is thrown.

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 reading.
Throws:
SecurityException - if a security manager exists and its checkRead method denies read access to the file descriptor.
See Also:
SecurityManager.checkRead(java.io.FileDescriptor)

Methods

read

public int read()
         throws IOException

Reads a byte of data from this input stream. This method blocks if no input is yet available.

Specified by:
read in class InputStream
Returns:
the next byte of data, or -1 if the end of the file is reached.
Throws:
IOException - if an I/O error occurs.

read

public int read(byte[] b)
         throws IOException

Reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.

Overrides:
read in class InputStream
Parameters:
b - the buffer into which the data is read.
Returns:
the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.
Throws:
IOException - if an I/O error occurs.
See Also:
InputStream.read(byte[], int, int)

read

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

Reads up to len bytes of data from this input stream into an array of bytes. If len is not zero, the method blocks until some input is available; otherwise, no bytes are read and 0 is returned.

Overrides:
read in class InputStream
Parameters:
b - the buffer into which the data is read.
off - the start offset in the destination array b
len - the maximum number of bytes read.
Returns:
the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.
Throws:
NullPointerException - If b is null.
IndexOutOfBoundsException - If off is negative, len is negative, or len is greater than b.length - off
IOException - if an I/O error occurs.
See Also:
InputStream.read()

skip

public long skip(long n)
          throws IOException

Skips over and discards n bytes of data from the input stream.

The skip method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly 0. If n is negative, the method will try to skip backwards. In case the backing file does not support backward skip at its current position, an IOException is thrown. The actual number of bytes skipped is returned. If it skips forwards, it returns a positive value. If it skips backwards, it returns a negative value.

This method may skip more bytes than what are remaining in the backing file. This produces no exception and the number of bytes skipped may include some number of bytes that were beyond the EOF of the backing file. Attempting to read from the stream after skipping past the end will result in -1 indicating the end of the file.

Overrides:
skip in class InputStream
Parameters:
n - the number of bytes to be skipped.
Returns:
the actual number of bytes skipped.
Throws:
IOException - if n is negative, if the stream does not support seek, or if an I/O error occurs.

available

public int available()
              throws IOException

Returns an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking by the next invocation of a method for this input stream. Returns 0 when the file position is beyond EOF. The next invocation might be the same thread or another thread. A single read or skip of this many bytes will not block, but may read or skip fewer bytes.

In some cases, a non-blocking read (or skip) may appear to be blocked when it is merely slow, for example when reading large files over slow networks.

Overrides:
available in class InputStream
Returns:
an estimate of the number of remaining bytes that can be read (or skipped over) from this input stream without blocking.
Throws:
IOException - if this file input stream has been closed by calling close or an I/O error occurs.

close

public void close()
           throws IOException

Closes this file input stream and releases any system resources associated with the stream.

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 InputStream
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 FileDescriptor object that represents the connection to the actual file in the file system being used by this FileInputStream.

Returns:
the file descriptor object associated with this stream.
Throws:
IOException - if an I/O error occurs.
See Also:
FileDescriptor

getChannel

public FileChannel getChannel()

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

The initial position of the returned channel will be equal to the number of bytes read from the file so far. Reading bytes from this stream will increment the channel's position. Changing the channel's position, either explicitly or by reading, will change this stream's file position.

Returns:
the file channel associated with this file input 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.

Ensures that the close() method of this file input stream is called when there are no more references to it. 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 FileInputStream 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.
Throws:
IOException - if an I/O error occurs.
See Also:
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/FileInputStream.html