Class FileInputStream
- All Implemented Interfaces:
Closeable
,AutoCloseable
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:
- The
close()
method should be called to release resources used by this stream, either directly, or with thetry
-with-resources statement. - Implementation Requirements:
- Subclasses are responsible for the cleanup of resources acquired by the subclass.
Subclasses requiring that resource cleanup take place after a stream becomes
unreachable should use
Cleaner
or some other mechanism. - Since:
- 1.0
- See Also:
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Constructor Summary
ConstructorDescriptionFileInputStream
(File file) Creates aFileInputStream
to read from an existing file represented by theFile
objectfile
.FileInputStream
(FileDescriptor fdObj) Creates aFileInputStream
by using the file descriptorfdObj
, which represents an existing connection to an actual file in the file system.FileInputStream
(String name) Creates aFileInputStream
to read from an existing file named by the path namename
. -
Method Summary
Modifier and TypeMethodDescriptionint
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.Returns the uniqueFileChannel
object associated with this file input stream.final FileDescriptor
getFD()
Returns theFileDescriptor
object that represents the connection to the actual file in the file system being used by thisFileInputStream
.int
read()
Reads a byte of data from this input stream.int
read
(byte[] b) Reads up tob.length
bytes of data from this input stream into an array of bytes.int
read
(byte[] b, int off, int len) Reads up tolen
bytes of data from this input stream into an array of bytes.byte[]
Reads all remaining bytes from the input stream.byte[]
readNBytes
(int len) Reads up to a specified number of bytes from the input stream.long
skip
(long n) Skips over and discardsn
bytes of data from the input stream.long
transferTo
(OutputStream out) Reads all bytes from this input stream and writes the bytes to the given output stream in the order that they are read.Methods inherited from class java.io.InputStream
mark, markSupported, nullInputStream, readNBytes, reset, skipNBytes
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Constructor Details
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FileInputStream
Creates aFileInputStream
to read from an existing file named by the path namename
. Symbolic links are automatically redirected to the target of the link. A newFileDescriptor
object is created to represent this file connection.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.
-
FileInputStream
Creates aFileInputStream
to read from an existing file represented by theFile
objectfile
. Symbolic links are automatically redirected to the target of the link. A newFileDescriptor
object is created to represent this file connection.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.- See Also:
-
FileInputStream
Creates aFileInputStream
by using the file descriptorfdObj
, which represents an existing connection to an actual file in the file system.If
fdObj
is null then aNullPointerException
is thrown.This constructor does not throw an exception if
fdObj
isinvalid
. However, if the methods are invoked on the resulting stream to attempt I/O on the stream, anIOException
is thrown.- Parameters:
fdObj
- the file descriptor to be opened for reading.
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Method Details
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read
Reads a byte of data from this input stream. This method blocks if no input is yet available.- Specified by:
read
in classInputStream
- 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
Reads up tob.length
bytes of data from this input stream into an array of bytes. This method blocks until some input is available.- Overrides:
read
in classInputStream
- 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:
-
read
Reads up tolen
bytes of data from this input stream into an array of bytes. Iflen
is not zero, the method blocks until some input is available; otherwise, no bytes are read and0
is returned.- Overrides:
read
in classInputStream
- Parameters:
b
- the buffer into which the data is read.off
- the start offset in arrayb
at which the data is written.len
- the maximum number of bytes to read.- Returns:
- the total number of bytes read into the buffer, or
-1
if there is no more data because the end of the stream has been reached. - Throws:
NullPointerException
- Ifb
isnull
.IndexOutOfBoundsException
- Ifoff
is negative,len
is negative, orlen
is greater thanb.length - off
IOException
- if an I/O error occurs.- See Also:
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readAllBytes
Description copied from class:InputStream
Reads all remaining bytes from the input stream. This method blocks until all remaining bytes have been read and end of stream is detected, or an exception is thrown. This method does not close the input stream.When this stream reaches end of stream, further invocations of this method will return an empty byte array.
Note that this method is intended for simple cases where it is convenient to read all bytes into a byte array. It is not intended for reading input streams with large amounts of data.
The behavior for the case where the input stream is asynchronously closed, or the thread interrupted during the read, is highly input stream specific, and therefore not specified.
If an I/O error occurs reading from the input stream, then it may do so after some, but not all, bytes have been read. Consequently the input stream may not be at end of stream and may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.
- Overrides:
readAllBytes
in classInputStream
- Returns:
- a byte array containing the bytes read from this input stream
- Throws:
IOException
- if an I/O error occurs
-
readNBytes
Description copied from class:InputStream
Reads up to a specified number of bytes from the input stream. This method blocks until the requested number of bytes has been read, end of stream is detected, or an exception is thrown. This method does not close the input stream.The length of the returned array equals the number of bytes read from the stream. If
len
is zero, then no bytes are read and an empty byte array is returned. Otherwise, up tolen
bytes are read from the stream. Fewer thanlen
bytes may be read if end of stream is encountered.When this stream reaches end of stream, further invocations of this method will return an empty byte array.
Note that this method is intended for simple cases where it is convenient to read the specified number of bytes into a byte array. The total amount of memory allocated by this method is proportional to the number of bytes read from the stream which is bounded by
len
. Therefore, the method may be safely called with very large values oflen
provided sufficient memory is available.The behavior for the case where the input stream is asynchronously closed, or the thread interrupted during the read, is highly input stream specific, and therefore not specified.
If an I/O error occurs reading from the input stream, then it may do so after some, but not all, bytes have been read. Consequently the input stream may not be at end of stream and may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.
- Overrides:
readNBytes
in classInputStream
- Parameters:
len
- the maximum number of bytes to read- Returns:
- a byte array containing the bytes read from this input stream
- Throws:
IOException
- if an I/O error occurs- Since:
- 11
-
transferTo
Reads all bytes from this input stream and writes the bytes to the given output stream in the order that they are read. On return, this input stream will be at end of stream. This method does not close either stream.This method may block indefinitely reading from the input stream, or writing to the output stream. The behavior for the case where the input and/or output stream is asynchronously closed, or the thread interrupted during the transfer, is highly input and output stream specific, and therefore not specified.
If the total number of bytes transferred is greater than Long.MAX_VALUE, then
Long.MAX_VALUE
will be returned.If an I/O error occurs reading from the input stream or writing to the output stream, then it may do so after some bytes have been read or written. Consequently the input stream may not be at end of stream and one, or both, streams may be in an inconsistent state. It is strongly recommended that both streams be promptly closed if an I/O error occurs.
- Overrides:
transferTo
in classInputStream
- Parameters:
out
- the output stream, non-null- Returns:
- the number of bytes transferred
- Throws:
IOException
- if an I/O error occurs when reading or writing
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skip
Skips over and discardsn
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, possibly0
. Ifn
is negative, the method will try to skip backwards. In case the backing file does not support backward skip at its current position, anIOException
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 classInputStream
- 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.- See Also:
-
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. 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 classInputStream
- 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 callingclose
or an I/O error occurs.
-
close
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 interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Overrides:
close
in classInputStream
- API Note:
- Overriding
close()
to perform cleanup actions is reliable only when called directly or when called by try-with-resources. - Implementation Requirements:
- Subclasses requiring that resource cleanup take place after a stream becomes
unreachable should use the
Cleaner
mechanism.If this stream has an associated channel then this method will close the channel, which in turn will close this stream. Subclasses that override this method should be prepared to handle possible reentrant invocation.
- Throws:
IOException
- if an I/O error occurs.
-
getFD
Returns theFileDescriptor
object that represents the connection to the actual file in the file system being used by thisFileInputStream
.- Returns:
- the file descriptor object associated with this stream.
- Throws:
IOException
- if an I/O error occurs.- See Also:
-
getChannel
Returns the uniqueFileChannel
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
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