392 lines
14 KiB
Java
392 lines
14 KiB
Java
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/*
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* Copyright (c) 1996, 2012, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.io;
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import java.nio.CharBuffer;
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import java.util.Objects;
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/**
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* Abstract class for reading character streams. The only methods that a
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* subclass must implement are read(char[], int, int) and close(). Most
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* subclasses, however, will override some of the methods defined here in order
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* to provide higher efficiency, additional functionality, or both.
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*
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*
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* @see BufferedReader
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* @see LineNumberReader
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* @see CharArrayReader
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* @see InputStreamReader
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* @see FileReader
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* @see FilterReader
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* @see PushbackReader
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* @see PipedReader
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* @see StringReader
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* @see Writer
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*
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* @author Mark Reinhold
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* @since 1.1
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*/
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public abstract class Reader implements Readable, Closeable {
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private static final int TRANSFER_BUFFER_SIZE = 8192;
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/**
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* Returns a new {@code Reader} that reads no characters. The returned
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* stream is initially open. The stream is closed by calling the
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* {@code close()} method. Subsequent calls to {@code close()} have no
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* effect.
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*
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* <p> While the stream is open, the {@code read()}, {@code read(char[])},
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* {@code read(char[], int, int)}, {@code read(Charbuffer)}, {@code
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* ready()}, {@code skip(long)}, and {@code transferTo()} methods all
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* behave as if end of stream has been reached. After the stream has been
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* closed, these methods all throw {@code IOException}.
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*
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* <p> The {@code markSupported()} method returns {@code false}. The
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* {@code mark()} and {@code reset()} methods throw an {@code IOException}.
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*
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* <p> The {@link #lock object} used to synchronize operations on the
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* returned {@code Reader} is not specified.
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*
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* @return a {@code Reader} which reads no characters
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*
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* @since 11
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*/
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public static Reader nullReader() {
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return new Reader() {
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private volatile boolean closed;
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private void ensureOpen() throws IOException {
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if (closed) {
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throw new IOException("Stream closed");
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}
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}
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@Override
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public int read() throws IOException {
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ensureOpen();
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return -1;
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}
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@Override
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public int read(char[] cbuf, int off, int len) throws IOException {
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Objects.checkFromIndexSize(off, len, cbuf.length);
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ensureOpen();
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if (len == 0) {
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return 0;
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}
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return -1;
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}
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@Override
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public int read(CharBuffer target) throws IOException {
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Objects.requireNonNull(target);
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ensureOpen();
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if (target.hasRemaining()) {
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return -1;
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}
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return 0;
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}
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@Override
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public boolean ready() throws IOException {
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ensureOpen();
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return false;
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}
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@Override
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public long skip(long n) throws IOException {
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ensureOpen();
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return 0L;
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}
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@Override
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public long transferTo(Writer out) throws IOException {
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Objects.requireNonNull(out);
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ensureOpen();
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return 0L;
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}
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@Override
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public void close() {
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closed = true;
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}
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};
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}
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/**
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* The object used to synchronize operations on this stream. For
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* efficiency, a character-stream object may use an object other than
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* itself to protect critical sections. A subclass should therefore use
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* the object in this field rather than {@code this} or a synchronized
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* method.
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*/
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protected Object lock;
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/**
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* Creates a new character-stream reader whose critical sections will
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* synchronize on the reader itself.
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*/
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protected Reader() {
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this.lock = this;
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}
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/**
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* Creates a new character-stream reader whose critical sections will
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* synchronize on the given object.
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*
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* @param lock The Object to synchronize on.
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*/
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protected Reader(Object lock) {
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if (lock == null) {
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throw new NullPointerException();
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}
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this.lock = lock;
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}
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/**
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* Attempts to read characters into the specified character buffer.
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* The buffer is used as a repository of characters as-is: the only
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* changes made are the results of a put operation. No flipping or
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* rewinding of the buffer is performed.
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*
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* @param target the buffer to read characters into
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* @return The number of characters added to the buffer, or
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* -1 if this source of characters is at its end
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* @throws IOException if an I/O error occurs
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* @throws NullPointerException if target is null
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* @throws java.nio.ReadOnlyBufferException if target is a read only buffer
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* @since 1.5
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*/
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public int read(java.nio.CharBuffer target) throws IOException {
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int len = target.remaining();
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char[] cbuf = new char[len];
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int n = read(cbuf, 0, len);
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if (n > 0)
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target.put(cbuf, 0, n);
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return n;
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}
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/**
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* Reads a single character. This method will block until a character is
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* available, an I/O error occurs, or the end of the stream is reached.
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*
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* <p> Subclasses that intend to support efficient single-character input
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* should override this method.
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*
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* @return The character read, as an integer in the range 0 to 65535
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* ({@code 0x00-0xffff}), or -1 if the end of the stream has
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* been reached
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*
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* @exception IOException If an I/O error occurs
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*/
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public int read() throws IOException {
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char cb[] = new char[1];
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if (read(cb, 0, 1) == -1)
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return -1;
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else
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return cb[0];
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}
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/**
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* Reads characters into an array. This method will block until some input
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* is available, an I/O error occurs, or the end of the stream is reached.
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*
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* @param cbuf Destination buffer
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*
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* @return The number of characters read, or -1
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* if the end of the stream
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* has been reached
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*
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* @exception IOException If an I/O error occurs
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*/
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public int read(char cbuf[]) throws IOException {
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return read(cbuf, 0, cbuf.length);
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}
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/**
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* Reads characters into a portion of an array. This method will block
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* until some input is available, an I/O error occurs, or the end of the
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* stream is reached.
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*
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* @param cbuf Destination buffer
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* @param off Offset at which to start storing characters
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* @param len Maximum number of characters to read
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*
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* @return The number of characters read, or -1 if the end of the
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* stream has been reached
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*
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* @exception IOException If an I/O error occurs
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* @exception IndexOutOfBoundsException
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* If {@code off} is negative, or {@code len} is negative,
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* or {@code len} is greater than {@code cbuf.length - off}
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*/
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public abstract int read(char cbuf[], int off, int len) throws IOException;
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/** Maximum skip-buffer size */
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private static final int maxSkipBufferSize = 8192;
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/** Skip buffer, null until allocated */
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private char skipBuffer[] = null;
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/**
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* Skips characters. This method will block until some characters are
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* available, an I/O error occurs, or the end of the stream is reached.
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*
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* @param n The number of characters to skip
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*
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* @return The number of characters actually skipped
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*
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* @exception IllegalArgumentException If <code>n</code> is negative.
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* @exception IOException If an I/O error occurs
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*/
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public long skip(long n) throws IOException {
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if (n < 0L)
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throw new IllegalArgumentException("skip value is negative");
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int nn = (int) Math.min(n, maxSkipBufferSize);
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synchronized (lock) {
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if ((skipBuffer == null) || (skipBuffer.length < nn))
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skipBuffer = new char[nn];
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long r = n;
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while (r > 0) {
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int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
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if (nc == -1)
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break;
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r -= nc;
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}
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return n - r;
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}
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}
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/**
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* Tells whether this stream is ready to be read.
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*
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* @return True if the next read() is guaranteed not to block for input,
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* false otherwise. Note that returning false does not guarantee that the
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* next read will block.
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*
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* @exception IOException If an I/O error occurs
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*/
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public boolean ready() throws IOException {
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return false;
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}
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/**
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* Tells whether this stream supports the mark() operation. The default
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* implementation always returns false. Subclasses should override this
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* method.
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*
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* @return true if and only if this stream supports the mark operation.
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*/
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public boolean markSupported() {
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return false;
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}
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/**
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* Marks the present position in the stream. Subsequent calls to reset()
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* will attempt to reposition the stream to this point. Not all
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* character-input streams support the mark() operation.
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*
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* @param readAheadLimit Limit on the number of characters that may be
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* read while still preserving the mark. After
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* reading this many characters, attempting to
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* reset the stream may fail.
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*
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* @exception IOException If the stream does not support mark(),
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* or if some other I/O error occurs
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*/
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public void mark(int readAheadLimit) throws IOException {
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throw new IOException("mark() not supported");
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}
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/**
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* Resets the stream. If the stream has been marked, then attempt to
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* reposition it at the mark. If the stream has not been marked, then
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* attempt to reset it in some way appropriate to the particular stream,
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* for example by repositioning it to its starting point. Not all
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* character-input streams support the reset() operation, and some support
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* reset() without supporting mark().
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*
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* @exception IOException If the stream has not been marked,
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* or if the mark has been invalidated,
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* or if the stream does not support reset(),
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* or if some other I/O error occurs
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*/
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public void reset() throws IOException {
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throw new IOException("reset() not supported");
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}
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/**
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* Closes the stream and releases any system resources associated with
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* it. Once the stream has been closed, further read(), ready(),
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* mark(), reset(), or skip() invocations will throw an IOException.
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* Closing a previously closed stream has no effect.
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*
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* @exception IOException If an I/O error occurs
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*/
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public abstract void close() throws IOException;
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/**
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* Reads all characters from this reader and writes the characters to the
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* given writer in the order that they are read. On return, this reader
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* will be at end of the stream. This method does not close either reader
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* or writer.
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* <p>
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* This method may block indefinitely reading from the reader, or
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* writing to the writer. The behavior for the case where the reader
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* and/or writer is <i>asynchronously closed</i>, or the thread
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* interrupted during the transfer, is highly reader and writer
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* specific, and therefore not specified.
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* <p>
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* If an I/O error occurs reading from the reader or writing to the
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* writer, then it may do so after some characters have been read or
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* written. Consequently the reader may not be at end of the stream and
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* one, or both, streams may be in an inconsistent state. It is strongly
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* recommended that both streams be promptly closed if an I/O error occurs.
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*
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* @param out the writer, non-null
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* @return the number of characters transferred
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* @throws IOException if an I/O error occurs when reading or writing
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* @throws NullPointerException if {@code out} is {@code null}
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*
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* @since 10
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*/
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public long transferTo(Writer out) throws IOException {
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Objects.requireNonNull(out, "out");
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long transferred = 0;
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char[] buffer = new char[TRANSFER_BUFFER_SIZE];
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int nRead;
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while ((nRead = read(buffer, 0, TRANSFER_BUFFER_SIZE)) >= 0) {
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out.write(buffer, 0, nRead);
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transferred += nRead;
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}
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return transferred;
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}
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|
}
|