Java 1.2 How-To/JavaHowTo.iso/3rdParty/jbuilder/unsupported/JDK1.2beta3/SOURCE/SRC.ZIP/java/io/BufferedReader.java

Java Source | 1998-03-20 | 10.9 KB | 399 lines

/*
 * @(#)BufferedReader.java    1.14 98/03/18
 *
 * Copyright 1996-1998 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     1.14, 98/03/18
 * @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.
     *
     * @param      skipLF  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 skipLF) 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;

                /* Skip a leftover '\n' */
        if (skipLF && (cb[nextChar] == '\n'))
                    nextChar++;

        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();
    }

    /**
     * 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 {
        return readLine(false);
    }

    /**
     * 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;
    }
    }

}