java.lang.Object | ||
↳ | java.io.InputStream | |
↳ | java.io.FileInputStream |
Known Direct Subclasses |
Known Indirect Subclasses |
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.
Public Constructors | |||||||||||
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Constructs a new
FileInputStream based on file . | |||||||||||
Constructs a new
FileInputStream on the file named
fileName . |
Public Methods | |||||||||||
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Returns an estimated number of bytes that can be read or skipped without blocking for more
input.
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Closes this stream.
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Returns the
FileChannel equivalent to this input stream. | |||||||||||
Returns the
FileDescriptor representing the operating system
resource for this stream. | |||||||||||
Reads bytes from this stream and stores them in the byte array
buffer . | |||||||||||
Reads a single byte from this stream and returns it as an integer in the
range from 0 to 255.
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Reads at most
count bytes from this stream and stores them in the
byte array buffer starting at offset . | |||||||||||
Skips
count number of bytes in this stream. |
Protected Methods | |||||||||||
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Ensures that all resources for this stream are released when it is about
to be garbage collected.
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Inherited Methods | |||||||||||
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From class java.io.InputStream
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From class java.lang.Object
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From interface java.io.Closeable
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Constructs a new FileInputStream
based on file
.
file | the file from which this stream reads. |
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FileNotFoundException | if file does not exist. |
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SecurityException | if a SecurityManager is installed and it denies the
read request.
|
Constructs a new FileInputStream
on the FileDescriptor
fd
. The file must already be open, therefore no
FileNotFoundException
will be thrown.
fd | the FileDescriptor from which this stream reads. |
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NullPointerException | if fd is null . |
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SecurityException | if a SecurityManager is installed and it denies the
read request.
|
Constructs a new FileInputStream
on the file named
fileName
. The path of fileName
may be absolute or
relative to the system property "user.dir"
.
fileName | the path and name of the file from which this stream reads. |
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FileNotFoundException | if there is no file named fileName . |
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SecurityException | if a SecurityManager is installed and it denies the
read request.
|
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.
IOException |
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Closes this stream.
IOException | if an error occurs attempting to close this stream. |
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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 FileDescriptor
representing the operating system
resource for this stream.
FileDescriptor
for this stream.IOException | if an error occurs while getting this stream's
FileDescriptor .
|
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Reads bytes from this stream and stores them in the byte array
buffer
.
buffer | the byte array in which to store the bytes read. |
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IOException | if this stream is closed or another I/O error occurs. |
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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.
IOException | if this stream is closed or another I/O error occurs. |
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Reads at most count
bytes from this stream and stores them in the
byte array buffer
starting at offset
.
buffer | the byte array in which to store the bytes read. |
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offset | the initial position in buffer to store the bytes read
from this stream. |
count | the maximum number of bytes to store in buffer . |
IndexOutOfBoundsException | if offset < 0 or count < 0 , or if
offset + count is greater than the size of
buffer . |
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IOException | if the stream is closed or another IOException occurs. |
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.
count | the number of bytes to skip. |
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IOException | if count < 0 , this stream is closed or unseekable,
or another IOException occurs.
|
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Ensures that all resources for this stream are released when it is about to be garbage collected.
IOException | if an error occurs attempting to finalize this stream. |
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