JDK8/Java8源码在线阅读

/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * 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
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * 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.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.io;

import java.nio.charset.Charset;
import java.nio.charset.CharsetEncoder;
import sun.nio.cs.StreamEncoder;


/**
 * An OutputStreamWriter is a bridge from character streams to byte streams:
 * Characters written to it are encoded into bytes using a specified {@link
 * java.nio.charset.Charset charset}.  The charset that it uses
 * may be specified by name or may be given explicitly, or the platform's
 * default charset may be accepted.
 *
 * <p> Each invocation of a write() method causes the encoding converter to be
 * invoked on the given character(s).  The resulting bytes are accumulated in a
 * buffer before being written to the underlying output stream.  The size of
 * this buffer may be specified, but by default it is large enough for most
 * purposes.  Note that the characters passed to the write() methods are not
 * buffered.
 *
 * <p> For top efficiency, consider wrapping an OutputStreamWriter within a
 * BufferedWriter so as to avoid frequent converter invocations.  For example:
 *
 * <pre>
 * Writer out
 *   = new BufferedWriter(new OutputStreamWriter(System.out));
 * </pre>
 *
 * <p> A <i>surrogate pair</i> is a character represented by a sequence of two
 * <tt>char</tt> values: A <i>high</i> surrogate in the range '&#92;uD800' to
 * '&#92;uDBFF' followed by a <i>low</i> surrogate in the range '&#92;uDC00' to
 * '&#92;uDFFF'.
 *
 * <p> A <i>malformed surrogate element</i> is a high surrogate that is not
 * followed by a low surrogate or a low surrogate that is not preceded by a
 * high surrogate.
 *
 * <p> This class always replaces malformed surrogate elements and unmappable
 * character sequences with the charset's default <i>substitution sequence</i>.
 * The {@linkplain java.nio.charset.CharsetEncoder} class should be used when more
 * control over the encoding process is required.
 *
 * @see BufferedWriter
 * @see OutputStream
 * @see java.nio.charset.Charset
 *
 * @author      Mark Reinhold
 * @since       JDK1.1
 */

public class OutputStreamWriter extends Writer {

    private final StreamEncoder se;

    /**
     * Creates an OutputStreamWriter that uses the named charset.
     *
     * @param  out
     *         An OutputStream
     *
     * @param  charsetName
     *         The name of a supported
     *         {@link java.nio.charset.Charset charset}
     *
     * @exception  UnsupportedEncodingException
     *             If the named encoding is not supported
     */
    public OutputStreamWriter(OutputStream out, String charsetName)
        throws UnsupportedEncodingException
    {
        super(out);
        if (charsetName == null)
            throw new NullPointerException("charsetName");
        se = StreamEncoder.forOutputStreamWriter(out, this, charsetName);
    }

    /**
     * Creates an OutputStreamWriter that uses the default character encoding.
     *
     * @param  out  An OutputStream
     */
    public OutputStreamWriter(OutputStream out) {
        super(out);
        try {
            se = StreamEncoder.forOutputStreamWriter(out, this, (String)null);
        } catch (UnsupportedEncodingException e) {
            throw new Error(e);
        }
    }

    /**
     * Creates an OutputStreamWriter that uses the given charset.
     *
     * @param  out
     *         An OutputStream
     *
     * @param  cs
     *         A charset
     *
     * @since 1.4
     * @spec JSR-51
     */
    public OutputStreamWriter(OutputStream out, Charset cs) {
        super(out);
        if (cs == null)
            throw new NullPointerException("charset");
        se = StreamEncoder.forOutputStreamWriter(out, this, cs);
    }

    /**
     * Creates an OutputStreamWriter that uses the given charset encoder.
     *
     * @param  out
     *         An OutputStream
     *
     * @param  enc
     *         A charset encoder
     *
     * @since 1.4
     * @spec JSR-51
     */
    public OutputStreamWriter(OutputStream out, CharsetEncoder enc) {
        super(out);
        if (enc == null)
            throw new NullPointerException("charset encoder");
        se = StreamEncoder.forOutputStreamWriter(out, this, enc);
    }

    /**
     * Returns the name of the character encoding being used by this stream.
     *
     * <p> If the encoding has an historical name then that name is returned;
     * otherwise the encoding's canonical name is returned.
     *
     * <p> If this instance was created with the {@link
     * #OutputStreamWriter(OutputStream, String)} constructor then the returned
     * name, being unique for the encoding, may differ from the name passed to
     * the constructor.  This method may return <tt>null</tt> if the stream has
     * been closed. </p>
     *
     * @return The historical name of this encoding, or possibly
     *         <code>null</code> if the stream has been closed
     *
     * @see java.nio.charset.Charset
     *
     * @revised 1.4
     * @spec JSR-51
     */
    public String getEncoding() {
        return se.getEncoding();
    }

    /**
     * Flushes the output buffer to the underlying byte stream, without flushing
     * the byte stream itself.  This method is non-private only so that it may
     * be invoked by PrintStream.
     */
    void flushBuffer() throws IOException {
        se.flushBuffer();
    }

    /**
     * Writes a single character.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void write(int c) throws IOException {
        se.write(c);
    }

    /**
     * Writes a portion of an array of characters.
     *
     * @param  cbuf  Buffer of characters
     * @param  off   Offset from which to start writing characters
     * @param  len   Number of characters to write
     *

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