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.
BufferedInputStream,
ByteArrayInputStream,
DataInputStream,
FilterInputStream,
read(),
OutputStream,
PushbackInputStream| 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 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 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.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 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 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.