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java.lang.Object
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+----java.io.InputStream
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+----java.io.FilterInputStream
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+----java.io.LineNumberInputStream
This class is an input stream filter that provides the added functionality of keeping track of the current line number.
A line is a sequence of bytes ending with a carriage return
character ('\r'), a newline character
('\n'), or a carriage return character followed
immediately by a linefeed character. In all three cases, the line
terminating character(s) are returned as a single newline character.
The line number begins at 0, and is incremented by
1 when a read returns a newline character.
LineNumberInputStream(InputStream)
available()
getLineNumber()
mark(int)
read()
read(byte[], int, int)
len bytes of data from this input stream
into an array of bytes.
reset()
mark method was last called on this input stream.
setLineNumber(int)
skip(long)
n bytes of data from the
input stream.
LineNumberInputStream
public LineNumberInputStream(InputStream in)
read
public 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.
The read method of
LineNumberInputStream calls the read
method of the underlying input stream. It checks for carriage
returns and newline characters in the input, and modifies the
current line number as appropriate. A carriage-return character or
a carriage return followed by a newline character are both
converted into a single newline character.
-1 if the end of this
stream is reached.
read
public int read(byte b[],
int off,
int len) throws IOException
len bytes of data from this input stream
into an array of bytes. This method blocks until some input is available.
The read method of
LineNumberInputStream repeatedly calls the
read method of zero arguments to fill in the byte array.
-1 if there is no more data because the end of
this stream has been reached.
setLineNumber
public void setLineNumber(int lineNumber)
getLineNumber
public int getLineNumber()
skip
public long skip(long n) throws IOException
n bytes of data from the
input stream. The skip method may, for a variety of
reasons, end up skipping over some smaller number of bytes,
possibly 0. The actual number of bytes skipped is returned.
The skip method of
LineNumberInputStream creates a byte array of length
n and then reads into it until n bytes
have been read or the end of the stream has been reached.
available
public int available() throws IOException
Note that if the underlying input stream is able to supply
k input characters without blocking, the
LineNumberInputStream can guarantee only to provide
k/2 characters without blocking, because the
k characters from the underlyhing input stream might
consist of k/2 pairs of '\r' and
'\n', which are converted to just
k/2 '\n' characters.
mark
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 mark method of
LineNumberInputStream remembers the current line
number in a private variable, and then calls the mark
method of the underlying input stream.
reset
public void reset() throws IOException
mark method was last called on this input stream.
The reset method of
LineNumberInputStream resets the line number to be
the line number at the time the mark method was
called, and then calls the reset method of the
underlying input stream.
Stream marks are intended to be used in situations where you need to read ahead a little to see what's in the stream. Often this is most easily done by invoking some general parser. If the stream is of the type handled by the parser, it just chugs along happily. If the stream is not of that type, the parser should toss an exception when it fails, which, if it happens within readlimit bytes, allows the outer code to reset the stream and try another parser.
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