public class

FileInputStream

extends InputStream
implements Closeable
java.lang.Object
   ↳ java.io.InputStream
     ↳ java.io.FileInputStream
Known Direct Subclasses
Known Indirect Subclasses

Class Overview

A specialized InputStream that reads from a file in the file system. All read requests made by calling methods in this class are directly forwarded to the equivalent function of the underlying operating system. Since this may induce some performance penalty, in particular if many small read requests are made, a FileInputStream is often wrapped by a BufferedInputStream.

See Also

Summary

Public Constructors
FileInputStream(File file)
Constructs a new FileInputStream based on file.
FileInputStream(FileDescriptor fd)
Constructs a new FileInputStream on the FileDescriptor fd.
FileInputStream(String fileName)
Constructs a new FileInputStream on the file named fileName.
Public Methods
int available()
Returns an estimated number of bytes that can be read or skipped without blocking for more input.
void close()
Closes this stream.
FileChannel getChannel()
Returns the FileChannel equivalent to this input stream.
final FileDescriptor getFD()
Returns the FileDescriptor representing the operating system resource for this stream.
int read(byte[] buffer, int offset, int count)
Reads at most count bytes from this stream and stores them in the byte array buffer starting at offset.
int read(byte[] buffer)
Reads bytes from this stream and stores them in the byte array buffer.
int read()
Reads a single byte from this stream and returns it as an integer in the range from 0 to 255.
long skip(long count)
Skips count number of bytes in this stream.
Protected Methods
void finalize()
Ensures that all resources for this stream are released when it is about to be garbage collected.
[Expand]
Inherited Methods
From class java.io.InputStream
From class java.lang.Object
From interface java.io.Closeable

Public Constructors

public FileInputStream (File file)

Since: API Level 1

Constructs a new FileInputStream based on file.

Parameters
file the file from which this stream reads.
Throws
FileNotFoundException if file does not exist.
SecurityException if a SecurityManager is installed and it denies the read request.

public FileInputStream (FileDescriptor fd)

Since: API Level 1

Constructs a new FileInputStream on the FileDescriptor fd. The file must already be open, therefore no FileNotFoundException will be thrown.

Parameters
fd the FileDescriptor from which this stream reads.
Throws
NullPointerException if fd is null.
SecurityException if a SecurityManager is installed and it denies the read request.

public FileInputStream (String fileName)

Since: API Level 1

Constructs a new FileInputStream on the file named fileName. The path of fileName may be absolute or relative to the system property "user.dir".

Parameters
fileName the path and name of the file from which this stream reads.
Throws
FileNotFoundException if there is no file named fileName.
SecurityException if a SecurityManager is installed and it denies the read request.

Public Methods

public int available ()

Since: API Level 1

Returns an estimated number of bytes that can be read or skipped without blocking for more input.

Note that this method provides such a weak guarantee that it is not very useful in practice.

Firstly, the guarantee is "without blocking for more input" rather than "without blocking": a read may still block waiting for I/O to complete — the guarantee is merely that it won't have to wait indefinitely for data to be written. The result of this method should not be used as a license to do I/O on a thread that shouldn't be blocked.

Secondly, the result is a conservative estimate and may be significantly smaller than the actual number of bytes available. In particular, an implementation that always returns 0 would be correct. In general, callers should only use this method if they'd be satisfied with treating the result as a boolean yes or no answer to the question "is there definitely data ready?".

Thirdly, the fact that a given number of bytes is "available" does not guarantee that a read or skip will actually read or skip that many bytes: they may read or skip fewer.

It is particularly important to realize that you must not use this method to size a container and assume that you can read the entirety of the stream without needing to resize the container. Such callers should probably write everything they read to a ByteArrayOutputStream and convert that to a byte array. Alternatively, if you're reading from a file, length() returns the current length of the file (though assuming the file's length can't change may be incorrect, reading a file is inherently racy).

The default implementation of this method in InputStream always returns 0. Subclasses should override this method if they are able to indicate the number of bytes available.

Returns
  • the estimated number of bytes available
Throws
IOException

public void close ()

Since: API Level 1

Closes this stream.

Throws
IOException if an error occurs attempting to close this stream.

public FileChannel getChannel ()

Since: API Level 1

Returns the FileChannel equivalent to this input stream.

The file channel is read-only and has an initial position within the file that is the same as the current position of this stream within the file. All changes made to the underlying file descriptor state via the channel are visible by the input stream and vice versa.

Returns
  • the file channel for this stream.

public final FileDescriptor getFD ()

Since: API Level 1

Returns the FileDescriptor representing the operating system resource for this stream.

Returns
  • the FileDescriptor for this stream.
Throws
IOException if an error occurs while getting this stream's FileDescriptor.

public int read (byte[] buffer, int offset, int count)

Since: API Level 1

Reads at most count bytes from this stream and stores them in the byte array buffer starting at offset.

Parameters
buffer the byte array in which to store the bytes read.
offset the initial position in buffer to store the bytes read from this stream.
count the maximum number of bytes to store in buffer.
Returns
  • the number of bytes actually read or -1 if the end of the stream has been reached.
Throws
IndexOutOfBoundsException if offset < 0 or count < 0, or if offset + count is greater than the size of buffer.
IOException if the stream is closed or another IOException occurs.

public int read (byte[] buffer)

Since: API Level 1

Reads bytes from this stream and stores them in the byte array buffer.

Parameters
buffer the byte array in which to store the bytes read.
Returns
  • the number of bytes actually read or -1 if the end of the stream has been reached.
Throws
IOException if this stream is closed or another I/O error occurs.

public int read ()

Since: API Level 1

Reads a single byte from this stream and returns it as an integer in the range from 0 to 255. Returns -1 if the end of this stream has been reached.

Returns
  • the byte read or -1 if the end of this stream has been reached.
Throws
IOException if this stream is closed or another I/O error occurs.

public long skip (long count)

Since: API Level 1

Skips count number of bytes in this stream. Subsequent read()s will not return these bytes unless reset() is used. If the underlying stream is unseekable, an IOException is thrown.

Parameters
count the number of bytes to skip.
Returns
  • the number of bytes actually skipped.
Throws
IOException if count < 0, this stream is closed or unseekable, or another IOException occurs.

Protected Methods

protected void finalize ()

Since: API Level 1

Ensures that all resources for this stream are released when it is about to be garbage collected.

Throws
IOException if an error occurs attempting to finalize this stream.