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
*
* @exception 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
*
* @exception 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
*
* @exception IOException If an I/O error occurs
* @exception 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
*
* @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");
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.
*
* @exception 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.
*
* @exception 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().
*
* @exception 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.
*
* @exception 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; } }