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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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package java.io;
import java.nio.CharBuffer;
import java.nio.ReadOnlyBufferException;
import java.util.Objects;
/**
* Abstract class for reading character streams. The only methods that a
* subclass must implement are read(char[], int, int) and close(). Most
* subclasses, however, will override some of the methods defined here in order
* to provide higher efficiency, additional functionality, or both.
*
*
* @see BufferedReader
* @see LineNumberReader
* @see CharArrayReader
* @see InputStreamReader
* @see FileReader
* @see FilterReader
* @see PushbackReader
* @see PipedReader
* @see StringReader
* @see Writer
*
* @author Mark Reinhold
* @since 1.1
*/
public abstract class Reader implements Readable, Closeable {
private static final int TRANSFER_BUFFER_SIZE = 8192;
/**
* Returns a new {@code Reader} that reads no characters. The returned
* stream is initially open. The stream is closed by calling the
* {@code close()} method. Subsequent calls to {@code close()} have no
* effect.
*
* 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(CharBuffer target) throws IOException {
if (target.isReadOnly())
throw new ReadOnlyBufferException();
int nread;
if (target.hasArray()) {
char[] cbuf = target.array();
int pos = target.position();
int rem = Math.max(target.limit() - pos, 0);
int off = target.arrayOffset() + pos;
nread = this.read(cbuf, off, rem);
if (nread > 0)
target.position(pos + nread);
} else {
int len = target.remaining();
char[] cbuf = new char[len];
nread = read(cbuf, 0, len);
if (nread > 0)
target.put(cbuf, 0, nread);
}
return nread;
}
/**
* 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.
*
*
If the length of {@code cbuf} is zero, then no characters are read
* and {@code 0} is returned; otherwise, there is an attempt to read at
* least one character. If no character is available because the stream is
* at its end, the value {@code -1} is returned; otherwise, at least one
* character is read and stored into {@code cbuf}.
*
* @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.
*
*
If {@code len} is zero, then no characters are read and {@code 0} is
* returned; otherwise, there is an attempt to read at least one character.
* If no character is available because the stream is at its end, the value
* {@code -1} is returned; otherwise, at least one character is read and
* stored into {@code cbuf}.
*
* @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 IndexOutOfBoundsException
* If {@code off} is negative, or {@code len} is negative,
* or {@code len} is greater than {@code cbuf.length - off}
* @throws IOException If an I/O error occurs
*/
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.
* If the stream is already at its end before this method is invoked,
* then no characters are skipped and zero is returned.
*
* @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;
}
}