The buffer size may be specified, or the default size may be used. The - * default is large enough for most purposes. - * - *
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, - * - *
- * BufferedReader in
- * = new BufferedReader(new FileReader("foo.in"));
- *
- *
- * 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.
- *
- * Programs that use DataInputStreams for textual input can be localized by - * replacing each DataInputStream with an appropriate BufferedReader. - * - * @see FileReader - * @see InputStreamReader - * @see java.nio.file.Files#newBufferedReader - * - * @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 */ - - /** If the next character is a line feed, skip it */ - private boolean skipLF = false; - - /** The skipLF flag when the mark was set */ - private boolean markedSkipLF = false; - - private static int defaultCharBufferSize = 8192; - private static int defaultExpectedLineLength = 80; - - /** - * Creates 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; - } - - /** - * Creates a buffering character-input stream that uses a default-sized - * input buffer. - * - * @param in A Reader - */ - public BufferedReader(Reader in) { - this(in, defaultCharBufferSize); - } - - /** Checks to make sure that the stream has not been closed */ - private void ensureOpen() throws IOException { - if (in == null) - throw new IOException("Stream closed"); - } - - /** - * Fills 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 accommodate read-ahead limit */ - char ncb[] = new char[readAheadLimit]; - System.arraycopy(cb, markedChar, ncb, 0, delta); - cb = ncb; - markedChar = 0; - dst = delta; - } - nextChar = nChars = delta; - } - } - - int n; - do { - n = in.read(cb, dst, cb.length - dst); - } while (n == 0); - if (n > 0) { - nChars = dst + n; - nextChar = dst; - } - } - - /** - * Reads a single character. - * - * @return The character read, as an integer in the range - * 0 to 65535 (0x00-0xffff), or -1 if the - * end of the stream has been reached - * @exception IOException If an I/O error occurs - */ - public int read() throws IOException { - synchronized (lock) { - ensureOpen(); - for (;;) { - if (nextChar >= nChars) { - fill(); - if (nextChar >= nChars) - return -1; - } - if (skipLF) { - skipLF = false; - if (cb[nextChar] == '\n') { - nextChar++; - continue; - } - } - return cb[nextChar++]; - } - } - } - - /** - * Reads characters into a portion of an array, reading from the underlying - * stream if necessary. - */ - private int read1(char[] cbuf, int off, int len) throws IOException { - if (nextChar >= nChars) { - /* If the requested length is at least as large as the buffer, and - if there is no mark/reset activity, and if line feeds are not - being skipped, do not bother to copy the characters into the - local buffer. In this way buffered streams will cascade - harmlessly. */ - if (len >= cb.length && markedChar <= UNMARKED && !skipLF) { - return in.read(cbuf, off, len); - } - fill(); - } - if (nextChar >= nChars) return -1; - if (skipLF) { - skipLF = false; - if (cb[nextChar] == '\n') { - nextChar++; - if (nextChar >= nChars) - fill(); - if (nextChar >= nChars) - return -1; - } - } - int n = Math.min(len, nChars - nextChar); - System.arraycopy(cb, nextChar, cbuf, off, n); - nextChar += n; - return n; - } - - /** - * Reads characters into a portion of an array. - * - *
This method implements the general contract of the corresponding
- * {@link Reader#read(char[], int, int) read} method of the
- * {@link Reader} class. As an additional convenience, it
- * attempts to read as many characters as possible by repeatedly invoking
- * the read method of the underlying stream. This iterated
- * read continues until one of the following conditions becomes
- * true:
read method of the underlying stream returns
- * -1, indicating end-of-file, or
- *
- * ready method of the underlying stream
- * returns false, indicating that further input requests
- * would block.
- *
- * read on the underlying stream returns
- * -1 to indicate end-of-file then this method returns
- * -1. Otherwise this method returns the number of characters
- * actually read.
- *
- * Subclasses of this class are encouraged, but not required, to - * attempt to read as many characters as possible in the same fashion. - * - *
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 BufferedReaders 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 characters 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 ((off < 0) || (off > cbuf.length) || (len < 0) ||
- ((off + len) > cbuf.length) || ((off + len) < 0)) {
- throw new IndexOutOfBoundsException();
- } else if (len == 0) {
- return 0;
- }
-
- int n = read1(cbuf, off, len);
- if (n <= 0) return n;
- while ((n < len) && in.ready()) {
- int n1 = read1(cbuf, off + n, len - n);
- if (n1 <= 0) break;
- n += n1;
- }
- return n;
- }
- }
-
- /**
- * Reads 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.
- *
- * @param ignoreLF If true, the next '\n' will be skipped
- *
- * @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
- *
- * @see java.io.LineNumberReader#readLine()
- *
- * @exception IOException If an I/O error occurs
- */
- String readLine(boolean ignoreLF) throws IOException {
- StringBuffer s = null;
- int startChar;
-
- synchronized (lock) {
- ensureOpen();
- boolean omitLF = ignoreLF || skipLF;
-
- bufferLoop:
- for (;;) {
-
- if (nextChar >= nChars)
- fill();
- if (nextChar >= nChars) { /* EOF */
- if (s != null && s.length() > 0)
- return s.toString();
- else
- return null;
- }
- boolean eol = false;
- char c = 0;
- int i;
-
- /* Skip a leftover '\n', if necessary */
- if (omitLF && (cb[nextChar] == '\n'))
- nextChar++;
- skipLF = false;
- omitLF = false;
-
- charLoop:
- for (i = nextChar; i < nChars; i++) {
- c = cb[i];
- if ((c == '\n') || (c == '\r')) {
- eol = true;
- break charLoop;
- }
- }
-
- startChar = nextChar;
- nextChar = i;
-
- if (eol) {
- String str;
- if (s == null) {
- str = new String(cb, startChar, i - startChar);
- } else {
- s.append(cb, startChar, i - startChar);
- str = s.toString();
- }
- nextChar++;
- if (c == '\r') {
- skipLF = true;
- }
- return str;
- }
-
- if (s == null)
- s = new StringBuffer(defaultExpectedLineLength);
- s.append(cb, startChar, i - startChar);
- }
- }
- }
-
- /**
- * Reads 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
- *
- * @see java.nio.file.Files#readAllLines
- */
- public String readLine() throws IOException {
- return readLine(false);
- }
-
- /**
- * Skips characters.
- *
- * @param n The number of characters to skip
- *
- * @return The number of characters actually skipped
- *
- * @exception IllegalArgumentException If n is negative.
- * @exception IOException If an I/O error occurs
- */
- public long skip(long n) throws IOException {
- if (n < 0L) {
- throw new IllegalArgumentException("skip value is negative");
- }
- synchronized (lock) {
- ensureOpen();
- long r = n;
- while (r > 0) {
- if (nextChar >= nChars)
- fill();
- if (nextChar >= nChars) /* EOF */
- break;
- if (skipLF) {
- skipLF = false;
- if (cb[nextChar] == '\n') {
- nextChar++;
- }
- }
- long d = nChars - nextChar;
- if (r <= d) {
- nextChar += r;
- r = 0;
- break;
- }
- else {
- r -= d;
- nextChar = nChars;
- }
- }
- return n - r;
- }
- }
-
- /**
- * Tells 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();
-
- /*
- * If newline needs to be skipped and the next char to be read
- * is a newline character, then just skip it right away.
- */
- if (skipLF) {
- /* Note that in.ready() will return true if and only if the next
- * read on the stream will not block.
- */
- if (nextChar >= nChars && in.ready()) {
- fill();
- }
- if (nextChar < nChars) {
- if (cb[nextChar] == '\n')
- nextChar++;
- skipLF = false;
- }
- }
- return (nextChar < nChars) || in.ready();
- }
- }
-
- /**
- * Tells whether this stream supports the mark() operation, which it does.
- */
- public boolean markSupported() {
- return true;
- }
-
- /**
- * Marks 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. An attempt
- * to reset the stream after reading characters
- * up to this limit or beyond 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;
- markedSkipLF = skipLF;
- }
- }
-
- /**
- * Resets 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;
- skipLF = markedSkipLF;
- }
- }
-
- public void close() throws IOException {
- synchronized (lock) {
- if (in == null)
- return;
- in.close();
- in = null;
- cb = null;
- }
- }
-}