Class InputStream
- All Implemented Interfaces:
Closeable
,AutoCloseable
- Direct Known Subclasses:
AudioInputStream
,ByteArrayInputStream
,FileInputStream
,FilterInputStream
,ObjectInputStream
,PipedInputStream
,SequenceInputStream
,StringBufferInputStream
Applications that need to define a subclass of InputStream
must always provide a method that returns the next byte of input.
- Since:
- 1.0
- See Also:
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Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionint
Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected.void
close()
Closes this input stream and releases any system resources associated with the stream.void
mark
(int readlimit) Marks the current position in this input stream.boolean
Tests if this input stream supports themark
andreset
methods.static InputStream
Returns a newInputStream
that reads no bytes.abstract int
read()
Reads the next byte of data from the input stream.int
read
(byte[] b) Reads some number of bytes from the input stream and stores them into the buffer arrayb
.int
read
(byte[] b, int off, int len) Reads up tolen
bytes of data from the input stream into an array of bytes.byte[]
Reads all remaining bytes from the input stream.int
readNBytes
(byte[] b, int off, int len) Reads the requested number of bytes from the input stream into the given byte array.byte[]
readNBytes
(int len) Reads up to a specified number of bytes from the input stream.void
reset()
Repositions this stream to the position at the time themark
method was last called on this input stream.long
skip
(long n) Skips over and discardsn
bytes of data from this input stream.void
skipNBytes
(long n) Skips over and discards exactlyn
bytes of data from this 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.
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Constructor Details
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InputStream
public InputStream()Constructor for subclasses to call.
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-
Method Details
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nullInputStream
Returns a newInputStream
that reads no bytes. The returned stream is initially open. The stream is closed by calling theclose()
method. Subsequent calls toclose()
have no effect.While the stream is open, the
available()
,read()
,read(byte[])
,read(byte[], int, int)
,readAllBytes()
,readNBytes(byte[], int, int)
,readNBytes(int)
,skip(long)
,skipNBytes(long)
, andtransferTo()
methods all behave as if end of stream has been reached. After the stream has been closed, these methods all throwIOException
.The
markSupported()
method returnsfalse
. Themark()
method does nothing, and thereset()
method throwsIOException
.- Returns:
- an
InputStream
which contains no bytes - Since:
- 11
-
read
Reads the next byte of data from the input stream. The value byte is returned as anint
in the range0
to255
. If no byte is available because the end of the stream has been reached, the value-1
is returned. This method blocks until input data is available, the end of the stream is detected, or an exception is thrown.- Returns:
- the next byte of data, or
-1
if the end of the stream is reached. - Throws:
IOException
- if an I/O error occurs.
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read
Reads some number of bytes from the input stream and stores them into the buffer arrayb
. The number of bytes actually read is returned as an integer. This method blocks until input data is available, end of file is detected, or an exception is thrown.If the length of
b
is zero, then no bytes are read and0
is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at the end of the file, the value-1
is returned; otherwise, at least one byte is read and stored intob
.The first byte read is stored into element
b[0]
, the next one intob[1]
, and so on. The number of bytes read is, at most, equal to the length ofb
. Let k be the number of bytes actually read; these bytes will be stored in elementsb[0]
throughb[
k-1]
, leaving elementsb[
k]
throughb[b.length-1]
unaffected.- Implementation Requirements:
- The
read(b)
method for classInputStream
has the same effect as:read(b, 0, b.length)
- 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 stream has been reached. - Throws:
IOException
- If the first byte cannot be read for any reason other than the end of the file, if the input stream has been closed, or if some other I/O error occurs.NullPointerException
- ifb
isnull
.- See Also:
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read
Reads up tolen
bytes of data from the input stream into an array of bytes. An attempt is made to read as many aslen
bytes, but a smaller number may be read. The number of bytes actually read is returned as an integer.This method blocks until input data is available, end of file is detected, or an exception is thrown.
If
len
is zero, then no bytes are read and0
is returned; otherwise, there is an attempt to read at least one byte. If no byte is available because the stream is at end of file, the value-1
is returned; otherwise, at least one byte is read and stored intob
.The first byte read is stored into element
b[off]
, the next one intob[off+1]
, and so on. The number of bytes read is, at most, equal tolen
. Let k be the number of bytes actually read; these bytes will be stored in elementsb[off]
throughb[off+
k-1]
, leaving elementsb[off+
k]
throughb[off+len-1]
unaffected.In every case, elements
b[0]
throughb[off-1]
and elementsb[off+len]
throughb[b.length-1]
are unaffected.- Implementation Requirements:
- The
read(b, off, len)
method for classInputStream
simply calls the methodread()
repeatedly. If the first such call results in anIOException
, that exception is returned from the call to theread(b,
off,
len)
method. If any subsequent call toread()
results in aIOException
, the exception is caught and treated as if it were end of file; the bytes read up to that point are stored intob
and the number of bytes read before the exception occurred is returned. The default implementation of this method blocks until the requested amount of input datalen
has been read, end of file is detected, or an exception is thrown. Subclasses are encouraged to provide a more efficient implementation of this method. - 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:
IOException
- If the first byte cannot be read for any reason other than end of file, or if the input stream has been closed, or if some other I/O error occurs.NullPointerException
- Ifb
isnull
.IndexOutOfBoundsException
- Ifoff
is negative,len
is negative, orlen
is greater thanb.length - off
- See Also:
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readAllBytes
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.
- Implementation Requirements:
- This method invokes
readNBytes(int)
with a length ofInteger.MAX_VALUE
. - Returns:
- a byte array containing the bytes read from this input stream
- Throws:
IOException
- if an I/O error occursOutOfMemoryError
- if an array of the required size cannot be allocated.- Since:
- 9
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readNBytes
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.
- Implementation Note:
- The number of bytes allocated to read data from this stream and return
the result is bounded by
2*(long)len
, inclusive. - Parameters:
len
- the maximum number of bytes to read- Returns:
- a byte array containing the bytes read from this input stream
- Throws:
IllegalArgumentException
- iflength
is negativeIOException
- if an I/O error occursOutOfMemoryError
- if an array of the required size cannot be allocated.- Since:
- 11
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readNBytes
Reads the requested number of bytes from the input stream into the given byte array. This method blocks untillen
bytes of input data have been read, end of stream is detected, or an exception is thrown. The number of bytes actually read, possibly zero, is returned. This method does not close the input stream.In the case where end of stream is reached before
len
bytes have been read, then the actual number of bytes read will be returned. When this stream reaches end of stream, further invocations of this method will return zero.If
len
is zero, then no bytes are read and0
is returned; otherwise, there is an attempt to read up tolen
bytes.The first byte read is stored into element
b[off]
, the next one in tob[off+1]
, and so on. The number of bytes read is, at most, equal tolen
. Let k be the number of bytes actually read; these bytes will be stored in elementsb[off]
throughb[off+
k-1]
, leaving elementsb[off+
k]
throughb[off+len-1]
unaffected.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 of
b
have been updated with data from the input stream. Consequently the input stream andb
may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.- Parameters:
b
- the byte array into which the data is readoff
- the start offset inb
at which the data is writtenlen
- the maximum number of bytes to read- Returns:
- the actual number of bytes read into the buffer
- Throws:
IOException
- if an I/O error occursNullPointerException
- ifb
isnull
IndexOutOfBoundsException
- Ifoff
is negative,len
is negative, orlen
is greater thanb.length - off
- Since:
- 9
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skip
Skips over and discardsn
bytes of data from this input stream. Theskip
method may, for a variety of reasons, end up skipping over some smaller number of bytes, possibly0
. This may result from any of a number of conditions; reaching end of file beforen
bytes have been skipped is only one possibility. The actual number of bytes skipped is returned. Ifn
is negative, theskip
method for classInputStream
always returns 0, and no bytes are skipped. Subclasses may handle the negative value differently.- Implementation Requirements:
- The
skip
method implementation of this class creates a byte array and then repeatedly reads into it untiln
bytes have been read or the end of the stream has been reached. Subclasses are encouraged to provide a more efficient implementation of this method. For instance, the implementation may depend on the ability to seek. - Parameters:
n
- the number of bytes to be skipped.- Returns:
- the actual number of bytes skipped which might be zero.
- Throws:
IOException
- if an I/O error occurs.- See Also:
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skipNBytes
Skips over and discards exactlyn
bytes of data from this input stream. Ifn
is zero, then no bytes are skipped. Ifn
is negative, then no bytes are skipped. Subclasses may handle the negative value differently.This method blocks until the requested number of bytes has been skipped, end of file is reached, or an exception is thrown.
If end of stream is reached before the stream is at the desired position, then an
EOFException
is thrown.If an I/O error occurs, then the input stream may be in an inconsistent state. It is strongly recommended that the stream be promptly closed if an I/O error occurs.
- Implementation Requirements:
- If
n
is zero or negative, then no bytes are skipped. Ifn
is positive, the default implementation of this method invokesskip()
repeatedly with its parameter equal to the remaining number of bytes to skip until the requested number of bytes has been skipped or an error condition occurs. If at any point the return value ofskip()
is negative or greater than the remaining number of bytes to be skipped, then anIOException
is thrown. Ifskip()
ever returns zero, thenread()
is invoked to read a single byte, and if it returns-1
, then anEOFException
is thrown. Any exception thrown byskip()
orread()
will be propagated. - Implementation Note:
- Subclasses are encouraged to provide a more efficient implementation of this method.
- Parameters:
n
- the number of bytes to be skipped.- Throws:
EOFException
- if end of stream is encountered before the stream can be positionedn
bytes beyond its position when this method was invoked.IOException
- if the stream cannot be positioned properly or if an I/O error occurs.- Since:
- 12
- See Also:
-
available
Returns an estimate of the number of bytes that can be read (or skipped over) from this input stream without blocking, which may be 0, or 0 when end of stream is detected. The read might be on 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.Note that while some implementations of
InputStream
will return the total number of bytes in the stream, many will not. It is never correct to use the return value of this method to allocate a buffer intended to hold all data in this stream.A subclass's implementation of this method may choose to throw an
IOException
if this input stream has been closed by invoking theclose()
method.- API Note:
- This method should be overridden by subclasses.
- Implementation Requirements:
- The
available
method ofInputStream
always returns0
. - Returns:
- an estimate of the number of bytes that can be read (or
skipped over) from this input stream without blocking or
0
when it reaches the end of the input stream. - Throws:
IOException
- if an I/O error occurs.
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close
Closes this input stream and releases any system resources associated with the stream.- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Implementation Requirements:
- The
close
method ofInputStream
does nothing. - Throws:
IOException
- if an I/O error occurs.
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mark
public void mark(int readlimit) Marks the current position in this input stream. A subsequent call to thereset
method repositions this stream at the last marked position so that subsequent reads re-read the same bytes.The
readlimit
arguments tells this input stream to allow that many bytes to be read before the mark position gets invalidated.The general contract of
mark
is that, if the methodmarkSupported
returnstrue
, the stream somehow remembers all the bytes read after the call tomark
and stands ready to supply those same bytes again if and whenever the methodreset
is called. However, the stream is not required to remember any data at all if more thanreadlimit
bytes are read from the stream beforereset
is called.Marking a closed stream should not have any effect on the stream.
- Implementation Requirements:
- The
mark
method ofInputStream
does nothing. - Parameters:
readlimit
- the maximum limit of bytes that can be read before the mark position becomes invalid.- See Also:
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reset
Repositions this stream to the position at the time themark
method was last called on this input stream.The general contract of
reset
is:- If the method
markSupported
returnstrue
, then:- If the method
mark
has not been called since the stream was created, or the number of bytes read from the stream sincemark
was last called is larger than the argument tomark
at that last call, then anIOException
might be thrown. - If such an
IOException
is not thrown, then the stream is reset to a state such that all the bytes read since the most recent call tomark
(or since the start of the file, ifmark
has not been called) will be resupplied to subsequent callers of theread
method, followed by any bytes that otherwise would have been the next input data as of the time of the call toreset
.
- If the method
- If the method
markSupported
returnsfalse
, then:- The call to
reset
may throw anIOException
. - If an
IOException
is not thrown, then the stream is reset to a fixed state that depends on the particular type of the input stream and how it was created. The bytes that will be supplied to subsequent callers of theread
method depend on the particular type of the input stream.
- The call to
- Implementation Requirements:
- The method
reset
for classInputStream
does nothing except throw anIOException
. - Throws:
IOException
- if this stream has not been marked or if the mark has been invalidated.- See Also:
- If the method
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markSupported
public boolean markSupported()Tests if this input stream supports themark
andreset
methods. Whether or notmark
andreset
are supported is an invariant property of a particular input stream instance.- Implementation Requirements:
- The
markSupported
method ofInputStream
returnsfalse
. - Returns:
true
if this stream instance supports the mark and reset methods;false
otherwise.- See Also:
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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.
- Parameters:
out
- the output stream, non-null- Returns:
- the number of bytes transferred
- Throws:
IOException
- if an I/O error occurs when reading or writingNullPointerException
- ifout
isnull
- Since:
- 9
-