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BufferedReader.java
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1998-09-22
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/*
* @(#)BufferedReader.java 1.12 98/07/01
*
* Copyright 1995-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
package java.io;
/**
* Read text from a character-input stream, buffering characters so as to
* provide for the efficient reading of characters, arrays, and lines.
*
* <p> The buffer size may be specified, or the default size may be used. The
* default is large enough for most purposes.
*
* <p> In general, each read request made of a Reader causes a corresponding
* read request to be made of the underlying character or byte stream. It is
* therefore advisable to wrap a BufferedReader around any Reader whose read()
* operations may be costly, such as FileReaders and InputStreamReaders. For
* example,
*
* <pre>
* BufferedReader in
* = new BufferedReader(new FileReader("foo.in"));
* </pre>
*
* will buffer the input from the specified file. Without buffering, each
* invocation of read() or readLine() could cause bytes to be read from the
* file, converted into characters, and then returned, which can be very
* inefficient.
*
* <p> Programs that use DataInputStreams for textual input can be localized by
* replacing each DataInputStream with an appropriate BufferedReader.
*
* @see FileReader
* @see InputStreamReader
*
* @version 1.12, 98/07/01
* @author Mark Reinhold
* @since JDK1.1
*/
public class BufferedReader extends Reader {
private Reader in;
private char cb[];
private int nChars, nextChar;
private static final int INVALIDATED = -2;
private static final int UNMARKED = -1;
private int markedChar = UNMARKED;
private int readAheadLimit = 0; /* Valid only when markedChar > 0 */
private static int defaultCharBufferSize = 8192;
private static int defaultExpectedLineLength = 80;
/**
* Create a buffering character-input stream that uses an input buffer of
* the specified size.
*
* @param in A Reader
* @param sz Input-buffer size
*
* @exception IllegalArgumentException If sz is <= 0
*/
public BufferedReader(Reader in, int sz) {
super(in);
if (sz <= 0)
throw new IllegalArgumentException("Buffer size <= 0");
this.in = in;
cb = new char[sz];
nextChar = nChars = 0;
}
/**
* Create a buffering character-input stream that uses a default-sized
* input buffer.
*
* @param in A Reader
*/
public BufferedReader(Reader in) {
this(in, defaultCharBufferSize);
}
/** Check to make sure that the stream has not been closed */
private void ensureOpen() throws IOException {
if (in == null)
throw new IOException("Stream closed");
}
/**
* Fill the input buffer, taking the mark into account if it is valid.
*/
private void fill() throws IOException {
int dst;
if (markedChar <= UNMARKED) {
/* No mark */
dst = 0;
} else {
/* Marked */
int delta = nextChar - markedChar;
if (delta >= readAheadLimit) {
/* Gone past read-ahead limit: Invalidate mark */
markedChar = INVALIDATED;
readAheadLimit = 0;
dst = 0;
} else {
if (readAheadLimit <= cb.length) {
/* Shuffle in the current buffer */
System.arraycopy(cb, markedChar, cb, 0, delta);
markedChar = 0;
dst = delta;
} else {
/* Reallocate buffer to accomodate read-ahead limit */
char ncb[] = new char[readAheadLimit];
System.arraycopy(cb, markedChar, ncb, 0, delta);
cb = ncb;
markedChar = 0;
dst = delta;
}
}
}
int n;
do {
n = in.read(cb, dst, cb.length - dst);
} while (n == 0);
if (n > 0) {
nChars = dst + n;
nextChar = dst;
}
}
/**
* Read a single character.
*
* @exception IOException If an I/O error occurs
*/
public int read() throws IOException {
synchronized (lock) {
ensureOpen();
if (nextChar >= nChars) {
fill();
if (nextChar >= nChars)
return -1;
}
return cb[nextChar++];
}
}
/**
* Read characters into a portion of an array.
*
* <p> Ordinarily this method takes characters from this stream's character
* buffer, filling it from the underlying stream as necessary. If,
* however, the buffer is empty, the mark is not valid, and the requested
* length is at least as large as the buffer, then this method will read
* characters directly from the underlying stream into the given array.
* Thus redundant <code>BufferedReader</code>s will not copy data
* unnecessarily.
*
* @param cbuf Destination buffer
* @param off Offset at which to start storing characters
* @param len Maximum number of characters to read
*
* @return The number of bytes read, or -1 if the end of the stream has
* been reached
*
* @exception IOException If an I/O error occurs
*/
public int read(char cbuf[], int off, int len) throws IOException {
synchronized (lock) {
ensureOpen();
if (nextChar >= nChars) {
/* If the requested length is larger than the buffer, and if
there is no mark/reset activity, do not bother to copy the
bytes into the local buffer. In this way buffered streams
will cascade harmlessly. */
if (len >= cb.length && markedChar <= UNMARKED) {
return in.read(cbuf, off, len);
}
fill();
}
if (nextChar >= nChars)
return -1;
int n = Math.min(len, nChars - nextChar);
System.arraycopy(cb, nextChar,
cbuf, off, n);
nextChar += n;
return n;
}
}
/**
* Read a line of text. A line is considered to be terminated by any one
* of a line feed ('\n'), a carriage return ('\r'), or a carriage return
* followed immediately by a linefeed.
*
* @return A String containing the contents of the line, not including
* any line-termination characters, or null if the end of the
* stream has been reached
*
* @exception IOException If an I/O error occurs
*/
public String readLine() throws IOException {
StringBuffer s = new StringBuffer(defaultExpectedLineLength);
synchronized (lock) {
ensureOpen();
bufferLoop:
for (;;) {
if (nextChar >= nChars)
fill();
if (nextChar >= nChars) { /* EOF */
if (s.length() > 0)
return s.toString();
else
return null;
}
boolean eol = false;
char c = 0;
int i;
charLoop:
for (i = nextChar; i < nChars; i++) {
c = cb[i];
if ((c == '\n') || (c == '\r')) {
eol = true;
break charLoop;
}
}
s.append(cb, nextChar, i - nextChar);
nextChar = i;
if (eol) {
nextChar++;
if (c == '\r') {
if (nextChar >= nChars)
fill();
if ((nextChar < nChars) && (cb[nextChar] == '\n'))
nextChar++;
}
break bufferLoop;
}
}
}
return s.toString();
}
/**
* Skip characters.
*
* @param n The number of characters to skip
*
* @return The number of characters actually skipped
*
* @exception IOException If an I/O error occurs
*/
public long skip(long n) throws IOException {
synchronized (lock) {
ensureOpen();
long r = n;
while (r > 0) {
if (nextChar >= nChars)
fill();
if (nextChar >= nChars) /* EOF */
break;
long d = nChars - nextChar;
if (r <= d) {
nextChar += r;
r = 0;
break;
}
else {
r -= d;
nextChar = nChars;
}
}
return n - r;
}
}
/**
* Tell whether this stream is ready to be read. A buffered character
* stream is ready if the buffer is not empty, or if the underlying
* character stream is ready.
*
* @exception IOException If an I/O error occurs
*/
public boolean ready() throws IOException {
synchronized (lock) {
ensureOpen();
return (nextChar < nChars) || in.ready();
}
}
/**
* Tell whether this stream supports the mark() operation, which it does.
*/
public boolean markSupported() {
return true;
}
/**
* Mark the present position in the stream. Subsequent calls to reset()
* will attempt to reposition the stream to this point.
*
* @param readAheadLimit Limit on the number of characters that may be
* read while still preserving the mark. After
* reading this many characters, attempting to
* reset the stream may fail. A limit value larger
* than the size of the input buffer will cause a
* new buffer to be allocated whose size is no
* smaller than limit. Therefore large values
* should be used with care.
*
* @exception IllegalArgumentException If readAheadLimit is < 0
* @exception IOException If an I/O error occurs
*/
public void mark(int readAheadLimit) throws IOException {
if (readAheadLimit < 0) {
throw new IllegalArgumentException("Read-ahead limit < 0");
}
synchronized (lock) {
ensureOpen();
this.readAheadLimit = readAheadLimit;
markedChar = nextChar;
}
}
/**
* Reset the stream to the most recent mark.
*
* @exception IOException If the stream has never been marked,
* or if the mark has been invalidated
*/
public void reset() throws IOException {
synchronized (lock) {
ensureOpen();
if (markedChar < 0)
throw new IOException((markedChar == INVALIDATED)
? "Mark invalid"
: "Stream not marked");
nextChar = markedChar;
}
}
/**
* Close the stream.
*
* @exception IOException If an I/O error occurs
*/
public void close() throws IOException {
synchronized (lock) {
if (in == null)
return;
in.close();
in = null;
cb = null;
}
}
}