While the stream is open, the {@code read()}, {@code read(char[])}, * {@code read(char[], int, int)}, {@code read(CharBuffer)}, {@code * ready()}, {@code skip(long)}, and {@code transferTo()} methods all * behave as if end of stream has been reached. After the stream has been * closed, these methods all throw {@code IOException}. * *
The {@code markSupported()} method returns {@code false}. The * {@code mark()} and {@code reset()} methods throw an {@code IOException}. * *
The {@link #lock object} used to synchronize operations on the * returned {@code Reader} is not specified. * * @return a {@code Reader} which reads no characters * * @since 11 */ public static Reader nullReader() { return new Reader() { private volatile boolean closed; private void ensureOpen() throws IOException { if (closed) { throw new IOException("Stream closed"); } } @Override public int read() throws IOException { ensureOpen(); return -1; } @Override public int read(char[] cbuf, int off, int len) throws IOException { Objects.checkFromIndexSize(off, len, cbuf.length); ensureOpen(); if (len == 0) { return 0; } return -1; } @Override public int read(CharBuffer target) throws IOException { Objects.requireNonNull(target); ensureOpen(); if (target.hasRemaining()) { return -1; } return 0; } @Override public boolean ready() throws IOException { ensureOpen(); return false; } @Override public long skip(long n) throws IOException { ensureOpen(); return 0L; } @Override public long transferTo(Writer out) throws IOException { Objects.requireNonNull(out); ensureOpen(); return 0L; } @Override public void close() { closed = true; } }; } /** * The object used to synchronize operations on this stream. For * efficiency, a character-stream object may use an object other than * itself to protect critical sections. A subclass should therefore use * the object in this field rather than {@code this} or a synchronized * method. */ protected Object lock; /** * Creates a new character-stream reader whose critical sections will * synchronize on the reader itself. */ protected Reader() { this.lock = this; } /** * Creates a new character-stream reader whose critical sections will * synchronize on the given object. * * @param lock The Object to synchronize on. */ protected Reader(Object lock) { if (lock == null) { throw new NullPointerException(); } this.lock = lock; } /** * Attempts to read characters into the specified character buffer. * The buffer is used as a repository of characters as-is: the only * changes made are the results of a put operation. No flipping or * rewinding of the buffer is performed. * * @param target the buffer to read characters into * @return The number of characters added to the buffer, or * -1 if this source of characters is at its end * @throws IOException if an I/O error occurs * @throws NullPointerException if target is null * @throws java.nio.ReadOnlyBufferException if target is a read only buffer * @since 1.5 */ public int read(java.nio.CharBuffer target) throws IOException { int len = target.remaining(); char[] cbuf = new char[len]; int n = read(cbuf, 0, len); if (n > 0) target.put(cbuf, 0, n); return n; } /** * Reads a single character. This method will block until a character is * available, an I/O error occurs, or the end of the stream is reached. * *
Subclasses that intend to support efficient single-character input * should override this method. * * @return The character read, as an integer in the range 0 to 65535 * ({@code 0x00-0xffff}), or -1 if the end of the stream has * been reached * * @throws IOException If an I/O error occurs */ public int read() throws IOException { char cb[] = new char[1]; if (read(cb, 0, 1) == -1) return -1; else return cb[0]; } /** * Reads characters into an array. This method will block until some input * is available, an I/O error occurs, or the end of the stream is reached. * * @param cbuf Destination buffer * * @return The number of characters read, or -1 * if the end of the stream * has been reached * * @throws IOException If an I/O error occurs */ public int read(char cbuf[]) throws IOException { return read(cbuf, 0, cbuf.length); } /** * Reads characters into a portion of an array. This method will block * until some input is available, an I/O error occurs, or the end of the * stream is reached. * * @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 * * @throws IOException If an I/O error occurs * @throws IndexOutOfBoundsException * If {@code off} is negative, or {@code len} is negative, * or {@code len} is greater than {@code cbuf.length - off} */ public abstract int read(char cbuf[], int off, int len) throws IOException; /** Maximum skip-buffer size */ private static final int maxSkipBufferSize = 8192; /** Skip buffer, null until allocated */ private char skipBuffer[] = null; /** * Skips characters. This method will block until some characters are * available, an I/O error occurs, or the end of the stream is reached. * * @param n The number of characters to skip * * @return The number of characters actually skipped * * @throws IllegalArgumentException If {@code n} is negative. * @throws IOException If an I/O error occurs */ public long skip(long n) throws IOException { if (n < 0L) throw new IllegalArgumentException("skip value is negative"); int nn = (int) Math.min(n, maxSkipBufferSize); synchronized (lock) { if ((skipBuffer == null) || (skipBuffer.length < nn)) skipBuffer = new char[nn]; long r = n; while (r > 0) { int nc = read(skipBuffer, 0, (int)Math.min(r, nn)); if (nc == -1) break; r -= nc; } return n - r; } } /** * Tells whether this stream is ready to be read. * * @return True if the next read() is guaranteed not to block for input, * false otherwise. Note that returning false does not guarantee that the * next read will block. * * @throws IOException If an I/O error occurs */ public boolean ready() throws IOException { return false; } /** * Tells whether this stream supports the mark() operation. The default * implementation always returns false. Subclasses should override this * method. * * @return true if and only if this stream supports the mark operation. */ public boolean markSupported() { return false; } /** * Marks the present position in the stream. Subsequent calls to reset() * will attempt to reposition the stream to this point. Not all * character-input streams support the mark() operation. * * @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. * * @throws IOException If the stream does not support mark(), * or if some other I/O error occurs */ public void mark(int readAheadLimit) throws IOException { throw new IOException("mark() not supported"); } /** * Resets the stream. If the stream has been marked, then attempt to * reposition it at the mark. If the stream has not been marked, then * attempt to reset it in some way appropriate to the particular stream, * for example by repositioning it to its starting point. Not all * character-input streams support the reset() operation, and some support * reset() without supporting mark(). * * @throws IOException If the stream has not been marked, * or if the mark has been invalidated, * or if the stream does not support reset(), * or if some other I/O error occurs */ public void reset() throws IOException { throw new IOException("reset() not supported"); } /** * Closes the stream and releases any system resources associated with * it. Once the stream has been closed, further read(), ready(), * mark(), reset(), or skip() invocations will throw an IOException. * Closing a previously closed stream has no effect. * * @throws IOException If an I/O error occurs */ public abstract void close() throws IOException; /** * Reads all characters from this reader and writes the characters to the * given writer in the order that they are read. On return, this reader * will be at end of the stream. This method does not close either reader * or writer. *
* This method may block indefinitely reading from the reader, or * writing to the writer. The behavior for the case where the reader * and/or writer is asynchronously closed, or the thread * interrupted during the transfer, is highly reader and writer * specific, and therefore not specified. *
* If an I/O error occurs reading from the reader or writing to the * writer, then it may do so after some characters have been read or * written. Consequently the reader may not be at end of the stream and * one, or both, streams may be in an inconsistent state. It is strongly * recommended that both streams be promptly closed if an I/O error occurs. * * @param out the writer, non-null * @return the number of characters transferred * @throws IOException if an I/O error occurs when reading or writing * @throws NullPointerException if {@code out} is {@code null} * * @since 10 */ public long transferTo(Writer out) throws IOException { Objects.requireNonNull(out, "out"); long transferred = 0; char[] buffer = new char[TRANSFER_BUFFER_SIZE]; int nRead; while ((nRead = read(buffer, 0, TRANSFER_BUFFER_SIZE)) >= 0) { out.write(buffer, 0, nRead); transferred += nRead; } return transferred; } }