public class PushbackInputStream extends FilterInputStream
InputStream and adds functionality to "push back"
bytes that have been read, so that they can be read again. Parsers may find
this useful. The number of bytes which may be pushed back can be specified
during construction. If the buffer of pushed back bytes is empty, bytes are
read from the underlying input stream.| Modifier and Type | Field and Description |
|---|---|
protected byte[] |
buf
The buffer that contains pushed-back bytes.
|
protected int |
pos
The current position within
buf. |
in| Constructor and Description |
|---|
PushbackInputStream(InputStream in)
Constructs a new
PushbackInputStream with the specified input
stream as source. |
PushbackInputStream(InputStream in,
int size)
Constructs a new
PushbackInputStream with in as source
input stream. |
| Modifier and Type | Method and Description |
|---|---|
int |
available()
Returns an estimated number of bytes that can be read or skipped without blocking for more
input.
|
void |
close()
Closes this stream.
|
void |
mark(int readlimit)
Marks the current position in this stream.
|
boolean |
markSupported()
Indicates whether this stream supports the
mark(int) and
reset() methods. |
int |
read()
Reads a single byte from this stream and returns it as an integer in the
range from 0 to 255.
|
int |
read(byte[] buffer,
int offset,
int length)
Reads at most
length bytes from this stream and stores them in
the byte array buffer starting at offset. |
void |
reset()
Resets this stream to the last marked position.
|
long |
skip(long byteCount)
Skips
byteCount bytes in this stream. |
void |
unread(byte[] buffer)
Pushes all the bytes in
buffer back to this stream. |
void |
unread(byte[] buffer,
int offset,
int length)
Pushes a subset of the bytes in
buffer back to this stream. |
void |
unread(int oneByte)
Pushes the specified byte
oneByte back to this stream. |
readprotected byte[] buf
protected int pos
buf. A value equal to
buf.length indicates that no bytes are available. A value of 0
indicates that the buffer is full.public PushbackInputStream(InputStream in)
PushbackInputStream with the specified input
stream as source. The size of the pushback buffer is set to the default
value of 1 byte.
Warning: passing a null source creates an invalid
PushbackInputStream. All read operations on such a stream will
fail.
in - the source input stream.public PushbackInputStream(InputStream in, int size)
PushbackInputStream with in as source
input stream. The size of the pushback buffer is set to size.
Warning: passing a null source creates an invalid
PushbackInputStream. All read operations on such a stream will
fail.
in - the source input stream.size - the size of the pushback buffer.IllegalArgumentException - if size is negative.public int available()
throws IOException
InputStreamNote 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, 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.
available in class FilterInputStreamIOException - if this stream is closed or an error occurspublic void close()
throws IOException
close in interface Closeableclose in interface AutoCloseableclose in class FilterInputStreamIOException - if an error occurs while closing this stream.public boolean markSupported()
mark(int) and
reset() methods. PushbackInputStream does not support
them, so it returns false.markSupported in class FilterInputStreamfalse.mark(int),
reset()public int read()
throws IOException
read in class FilterInputStreamIOException - if this stream is closed or an I/O error occurs while reading
from this stream.public int read(byte[] buffer,
int offset,
int length)
throws IOException
length bytes from this stream and stores them in
the byte array buffer starting at offset. Bytes are read
from the pushback buffer first, then from the source stream if more bytes
are required. Blocks until count bytes have been read, the end of
the source stream is detected or an exception is thrown.read in class FilterInputStreambuffer - the array in which to store the bytes read from this stream.offset - the initial position in buffer to store the bytes read
from this stream.length - the maximum number of bytes to store in buffer.IndexOutOfBoundsException - if offset < 0 or length < 0, or if
offset + length is greater than the length of
buffer.IOException - if this stream is closed or another I/O error occurs while
reading from this stream.NullPointerException - if buffer is null.public long skip(long byteCount)
throws IOException
byteCount bytes in this stream. This implementation skips bytes
in the pushback buffer first and then in the source stream if necessary.skip in class FilterInputStreambyteCount - the number of bytes to skip.IOException - if this stream is closed or another I/O error occurs.FilterInputStream.mark(int),
FilterInputStream.reset()public void unread(byte[] buffer)
throws IOException
buffer back to this stream. The bytes are
pushed back in such a way that the next byte read from this stream is
buffer[0], then buffer[1] and so on.
If this stream's internal pushback buffer cannot store the entire
contents of buffer, an IOException is thrown. Parts of
buffer may have already been copied to the pushback buffer when
the exception is thrown.
buffer - the buffer containing the bytes to push back to this stream.IOException - if the free space in the internal pushback buffer is not
sufficient to store the contents of buffer.public void unread(byte[] buffer,
int offset,
int length)
throws IOException
buffer back to this stream. The
subset is defined by the start position offset within
buffer and the number of bytes specified by length. The
bytes are pushed back in such a way that the next byte read from this
stream is buffer[offset], then buffer[1] and so on.
If this stream's internal pushback buffer cannot store the selected
subset of buffer, an IOException is thrown. Parts of
buffer may have already been copied to the pushback buffer when
the exception is thrown.
buffer - the buffer containing the bytes to push back to this stream.offset - the index of the first byte in buffer to push back.length - the number of bytes to push back.IndexOutOfBoundsException - if offset < 0 or length < 0, or if
offset + length is greater than the length of
buffer.IOException - if the free space in the internal pushback buffer is not
sufficient to store the selected contents of buffer.public void unread(int oneByte)
throws IOException
oneByte back to this stream. Only the
least significant byte of the integer oneByte is pushed back.
This is done in such a way that the next byte read from this stream is
(byte) oneByte.
If this stream's internal pushback buffer cannot store the byte, an
IOException is thrown.
oneByte - the byte to push back to this stream.IOException - if this stream is closed or the internal pushback buffer is
full.public void mark(int readlimit)
mark in class FilterInputStreamreadlimit - the number of bytes that can be read from this stream before
the mark is invalidated; this parameter is ignored.FilterInputStream.markSupported(),
FilterInputStream.reset()public void reset()
throws IOException
IOException.reset in class FilterInputStreamIOException - if this method is called.FilterInputStream.mark(int),
FilterInputStream.markSupported()