public abstract class InputStream extends Object implements Closeable
Applications that need to define a subclass of InputStream must always provide a
method that returns the next byte of input.
ByteArrayInputStream,
DataInputStream,
FilterInputStream,
read(),
OutputStream| Constructor and Description |
|---|
InputStream() |
| Modifier and Type | Method and Description |
|---|---|
int |
available()
Returns an estimate of the number of 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 input stream and releases any system resources associated with the stream.
|
void |
mark(int readlimit)
Marks the current position in this input stream.
|
boolean |
markSupported()
Tests if this input stream supports the
mark and reset methods. |
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 array
b. |
int |
read(byte[] b,
int off,
int len)
Reads up to
len bytes of data from the input stream into an array of bytes. |
void |
reset()
Repositions this stream to the position at the time the
mark method was last called
on this input stream. |
long |
skip(long n)
Skips over and discards
n bytes of data from this input stream. |
public int available()
throws IOException
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' implementation of this method may choose to throw an IOException if this
input stream has been closed by invoking the close() method.
The available method for class InputStream always returns 0.
This method should be overridden by subclasses.
0 when it reaches the end of the input stream.IOException - if an I/O error occurs.public void close()
throws IOException
The close method of InputStream does nothing.
close in interface Closeableclose in interface AutoCloseableIOException - if an I/O error occurs.public void mark(int readlimit)
reset
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 method markSupported
returns true, the stream somehow remembers all the bytes read after the call to
mark and stands ready to supply those same bytes again if and whenever the method
reset is called. However, the stream is not required to remember any data at all if
more than readlimit bytes are read from the stream before reset is
called.
Marking a closed stream should not have any effect on the stream.
The mark method of InputStream does nothing.
readlimit - the maximum limit of bytes that can be read before the mark position becomes invalid.reset()public boolean markSupported()
mark and reset methods. Whether
or not mark and reset are supported is an invariant property of a
particular input stream instance. The markSupported method of
InputStream returns false.public abstract int read()
throws IOException
int in the range 0 to 255. 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.
A subclass must provide an implementation of this method.
-1 if the end of the stream is reached.IOException - if an I/O error occurs.public int read(byte[] b)
throws IOException
b. 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 and 0 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 into b.
The first byte read is stored into element b[0], the next one into
b[1], and so on. The number of bytes read is, at most, equal to the length of
b. Let k be the number of bytes actually read; these bytes will be stored in
elements b[0] through b[k-1], leaving elements
b[k] through b[b.length-1] unaffected.
The read(b) method for class InputStream has the same effect as:
read(b, 0, b.length)
b - the buffer into which the data is read.-1 if there is no more
data because the end of the stream has been reached.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 - if b is null.read(byte[], int, int)public int read(byte[] b,
int off,
int len)
throws IOException
len bytes of data from the input stream into an array of bytes. An
attempt is made to read as many as len 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 and 0 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 into b.
The first byte read is stored into element b[off], the next one into
b[off+1], and so on. The number of bytes read is, at most, equal to
len. Let k be the number of bytes actually read; these bytes will be stored
in elements b[off] through b[off+k-1], leaving
elements b[off+k] through b[off+len-1] unaffected.
In every case, elements b[0] through b[off] and elements
b[off+len] through b[b.length-1] are unaffected.
The read(b, off, len) method for class
InputStream simply calls the method read() repeatedly. If the first
such call results in an IOException, that exception is returned from the call to the
read(b, off, len) method. If any subsequent call to
read() results in a IOException, the exception is caught and treated as
if it were end of file; the bytes read up to that point are stored into b 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 data len 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.
b - the buffer into which the data is read.off - the start offset in array b at which the data is written.len - the maximum number of bytes to read.-1 if there is no more
data because the end of the stream has been reached.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 - If b is null.IndexOutOfBoundsException - If off is negative, len is negative, or len is
greater than b.length - offread()public void reset()
throws IOException
mark method was last called
on this input stream.
The general contract of reset is:
markSupported returns true, then:
mark has not been called since the stream was created, or the
number of bytes read from the stream since mark was last called is larger than the
argument to mark at that last call, then an IOException might be
thrown.
IOException is not thrown, then the stream is reset to a state such
that all the bytes read since the most recent call to mark (or since the start of
the file, if mark has not been called) will be resupplied to subsequent callers of
the read method, followed by any bytes that otherwise would have been the next input
data as of the time of the call to reset.
markSupported returns false, then:
reset may throw an IOException.
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 the read method depend on the particular type of
the input stream.
The method reset for class InputStream does nothing except throw an
IOException.
IOException - if this stream has not been marked or if the mark has been invalidated.mark(int),
IOExceptionpublic long skip(long n)
throws IOException
n bytes of data from this input stream. The
skip method may, for a variety of reasons, end up skipping over some smaller number
of bytes, possibly 0. This may result from any of a number of conditions; reaching
end of file before n bytes have been skipped is only one possibility. The actual
number of bytes skipped is returned. If n is negative, no bytes are skipped.
The skip method of this class creates a byte array and then repeatedly reads into it
until n 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.
n - the number of bytes to be skipped.IOException - if the stream does not support seek, or if some other I/O error occurs.