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;
+ }
+ }
+}