src/java.base/share/classes/java/io/InputStreamReader.java

/*
 * Copyright (c) 1996, 2025, 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.CharBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import sun.nio.cs.StreamDecoder;

/**
 * An InputStreamReader is a bridge from byte streams to character streams: It
 * reads bytes and decodes them into characters using a specified {@link
 * Charset charset}.  The charset that it uses
 * may be specified by name or may be given explicitly, or the
 * {@link Charset#defaultCharset() default charset} may be used.
 *
 * <p> Each invocation of one of an InputStreamReader's read() methods may
 * cause one or more bytes to be read from the underlying byte-input stream.
 * To enable the efficient conversion of bytes to characters, more bytes may
 * be read ahead from the underlying stream than are necessary to satisfy the
 * current read operation.
 *
 * <p> For top efficiency, consider wrapping an InputStreamReader within a
 * BufferedReader.  For example:
 *
 * {@snippet lang=java :
 *     BufferedReader in = new BufferedReader(new InputStreamReader(anInputStream));
 * }
 *
 * <P>To read from {@link System#in}, use the system property value
 * {@link System##stdin.encoding stdin.encoding} as the {@code Charset}:
 *
 * {@snippet lang=java :
 *     new InputStreamReader(System.in, System.getProperty("stdin.encoding"));
 * }
 *
 * @see BufferedReader
 * @see InputStream
 * @see Charset
 * @see System##stdin.encoding stdin.encoding
 *
 * @author      Mark Reinhold
 * @since       1.1
 */

public class InputStreamReader extends Reader {
    private final StreamDecoder sd;

    /**
     * Creates an InputStreamReader that uses the
     * {@link Charset#defaultCharset() default charset}.
     *
     * @param  in   An InputStream
     *
     * @see Charset#defaultCharset()
     */
    @SuppressWarnings("this-escape")
    public InputStreamReader(InputStream in) {
        super(in);
        Charset cs = Charset.defaultCharset();
        sd = StreamDecoder.forInputStreamReader(in, this, cs);
    }

    /**
     * Creates an InputStreamReader that uses the named charset.
     *
     * @param  in
     *         An InputStream
     *
     * @param  charsetName
     *         The name of a supported {@link Charset charset}
     *
     * @throws     UnsupportedEncodingException
     *             If the named charset is not supported
     */
    @SuppressWarnings("this-escape")
    public InputStreamReader(InputStream in, String charsetName)
        throws UnsupportedEncodingException
    {
        super(in);
        if (charsetName == null)
            throw new NullPointerException("charsetName");
        sd = StreamDecoder.forInputStreamReader(in, this, charsetName);
    }

    /**
     * Creates an InputStreamReader that uses the given charset.
     *
     * @param  in       An InputStream
     * @param  cs       A charset
     *
     * @since 1.4
     */
    @SuppressWarnings("this-escape")
    public InputStreamReader(InputStream in, Charset cs) {
        super(in);
        if (cs == null)
            throw new NullPointerException("charset");
        sd = StreamDecoder.forInputStreamReader(in, this, cs);
    }

    /**
     * Creates an InputStreamReader that uses the given charset decoder.
     *
     * @param  in       An InputStream
     * @param  dec      A charset decoder
     *
     * @since 1.4
     */
    @SuppressWarnings("this-escape")
    public InputStreamReader(InputStream in, CharsetDecoder dec) {
        super(in);
        if (dec == null)
            throw new NullPointerException("charset decoder");
        sd = StreamDecoder.forInputStreamReader(in, this, dec);
    }

    /**
     * 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
     * #InputStreamReader(InputStream, String)} constructor then the returned
     * name, being unique for the encoding, may differ from the name passed to
     * the constructor. This method will return {@code null} if the
     * stream has been closed.
     * </p>
     * @return The historical name of this encoding, or
     *         {@code null} if the stream has been closed
     *
     * @see Charset
     */
    public String getEncoding() {
        return sd.getEncoding();
    }

    public int read(CharBuffer target) throws IOException {
        return sd.read(target);
    }

    /**
     * Reads a single character.
     *
     * @return The character read, or -1 if the end of the stream has been
     *         reached
     *
     * @throws     IOException  If an I/O error occurs
     */
    public int read() throws IOException {
        return sd.read();
    }

    /**
     * {@inheritDoc}
     * @throws     IndexOutOfBoundsException  {@inheritDoc}
     */
    public int read(char[] cbuf, int off, int len) throws IOException {
        return sd.read(cbuf, off, len);
    }

    /**
     * Tells whether this stream is ready to be read.  An InputStreamReader is
     * ready if its input buffer is not empty, or if bytes are available to be
     * read from the underlying byte stream.
     *
     * @throws     IOException  If an I/O error occurs
     */
    public boolean ready() throws IOException {
        return sd.ready();
    }

    public void close() throws IOException {
        sd.close();
    }
}