java.lang.Object | |
↳ | java.io.InputStream |
Known Direct Subclasses |
The base class for all input streams. An input stream is a means of reading data from a source in a byte-wise manner.
Some input streams also support marking a position in the input stream and
returning to this position later. This abstract class does not provide a
fully working implementation, so it needs to be subclassed, and at least the
read()
method needs to be overridden. Overriding some of the
non-abstract methods is also often advised, since it might result in higher
efficiency.
Many specialized input streams for purposes like reading from a file already exist in this package.
Public Constructors | |||||||||||
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This constructor does nothing.
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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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Sets a mark position in this InputStream.
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Indicates whether this stream supports the
mark() and
reset() methods. | |||||||||||
Reads bytes from this stream and stores them in the byte array
b . | |||||||||||
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
length bytes from this stream and stores them in
the byte array b starting at offset . | |||||||||||
Resets this stream to the last marked location.
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Skips at most
n bytes in this stream. |
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Inherited Methods | |||||||||||
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From class java.lang.Object
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From interface java.io.Closeable
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This constructor does nothing. It is provided for signature compatibility.
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 | if this stream is closed or an error occurs |
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Closes this stream. Concrete implementations of this class should free any resources during close. This implementation does nothing.
IOException | if an error occurs while closing this stream. |
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Sets a mark position in this InputStream. The parameter readlimit
indicates how many bytes can be read before the mark is invalidated.
Sending reset()
will reposition the stream back to the marked
position provided readLimit
has not been surpassed.
This default implementation does nothing and concrete subclasses must provide their own implementation.
readlimit | the number of bytes that can be read from this stream before the mark is invalidated. |
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Reads bytes from this stream and stores them in the byte array b
.
b | the byte array in which to store the bytes read. |
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IOException | if this stream is closed or another IOException 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 the stream has been reached. Blocks until one byte has been read, the end of the source stream is detected or an exception is thrown.
IOException | if the stream is closed or another IOException occurs. |
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Reads at most length
bytes from this stream and stores them in
the byte array b
starting at offset
.
b | 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. |
length | the maximum number of bytes to store in b . |
IndexOutOfBoundsException | if offset < 0 or length < 0 , or if
offset + length is greater than the length of
b . |
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IOException | if the stream is closed or another IOException occurs. |
Resets this stream to the last marked location. Throws an
IOException
if the number of bytes read since the mark has been
set is greater than the limit provided to mark
, or if no mark
has been set.
This implementation always throws an IOException
and concrete
subclasses should provide the proper implementation.
IOException | if this stream is closed or another IOException occurs. |
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Skips at most n
bytes in this stream. This method does nothing and returns
0 if n
is negative.
Note the "at most" in the description of this method: this method may choose to skip fewer bytes than requested. Callers should always check the return value.
This default implementation reads bytes into a temporary buffer. Concrete subclasses should provide their own implementation.
byteCount | the number of bytes to skip. |
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IOException | if this stream is closed or another IOException occurs. |
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