java/12 : java.base/java/nio/channels/Channels.java

Channels
https://openjdk.java.net/
GPLv2 + Classpath Exception
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.nio.channels;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Reader;
import java.io.Writer;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CharsetEncoder;
import java.nio.charset.UnsupportedCharsetException;
import java.nio.channels.spi.AbstractInterruptibleChannel;
import java.util.Objects;
import java.util.concurrent.ExecutionException;
import sun.nio.ch.ChannelInputStream;
import sun.nio.cs.StreamDecoder;
import sun.nio.cs.StreamEncoder;


Utility methods for channels and streams.
 This class defines static methods that support the interoperation of the stream classes of the io package with the channel classes of this package. 
Author: Mark Reinhold, Mike McCloskey, JSR-51 Expert Group
Since: 1.4/**
 * Utility methods for channels and streams.
 *
 * <p> This class defines static methods that support the interoperation of the
 * stream classes of the {@link java.io} package with the channel classes
 * of this package.  </p>
 *
 *
 * @author Mark Reinhold
 * @author Mike McCloskey
 * @author JSR-51 Expert Group
 * @since 1.4
 */

public final class Channels {

    private Channels() { throw new Error("no instances"); }

    Write all remaining bytes in buffer to the given channel.
If the channel is selectable then it must be configured blocking.
/**
     * Write all remaining bytes in buffer to the given channel.
     * If the channel is selectable then it must be configured blocking.
     */
    private static void writeFullyImpl(WritableByteChannel ch, ByteBuffer bb)
        throws IOException
    {
        while (bb.remaining() > 0) {
            int n = ch.write(bb);
            if (n <= 0)
                throw new RuntimeException("no bytes written");
        }
    }

    Write all remaining bytes in buffer to the given channel.
Throws: IllegalBlockingModeException – 
         If the channel is selectable and configured non-blocking./**
     * Write all remaining bytes in buffer to the given channel.
     *
     * @throws  IllegalBlockingModeException
     *          If the channel is selectable and configured non-blocking.
     */
    private static void writeFully(WritableByteChannel ch, ByteBuffer bb)
        throws IOException
    {
        if (ch instanceof SelectableChannel) {
            SelectableChannel sc = (SelectableChannel) ch;
            synchronized (sc.blockingLock()) {
                if (!sc.isBlocking())
                    throw new IllegalBlockingModeException();
                writeFullyImpl(ch, bb);
            }
        } else {
            writeFullyImpl(ch, bb);
        }
    }

    // -- Byte streams from channels --

    Constructs a stream that reads bytes from the given channel.
 The read methods of the resulting stream will throw an IllegalBlockingModeException if invoked while the underlying channel is in non-blocking mode. The stream will not be buffered, and it will not support the mark or reset methods. The stream will be safe for access by multiple concurrent threads. Closing the stream will in turn cause the channel to be closed. 
Params: ch – 
        The channel from which bytes will be read
Returns:  A new input stream/**
     * Constructs a stream that reads bytes from the given channel.
     *
     * <p> The {@code read} methods of the resulting stream will throw an
     * {@link IllegalBlockingModeException} if invoked while the underlying
     * channel is in non-blocking mode.  The stream will not be buffered, and
     * it will not support the {@link InputStream#mark mark} or {@link
     * InputStream#reset reset} methods.  The stream will be safe for access by
     * multiple concurrent threads.  Closing the stream will in turn cause the
     * channel to be closed.  </p>
     *
     * @param  ch
     *         The channel from which bytes will be read
     *
     * @return  A new input stream
     */
    public static InputStream newInputStream(ReadableByteChannel ch) {
        Objects.requireNonNull(ch, "ch");
        return new ChannelInputStream(ch);
    }

    Constructs a stream that writes bytes to the given channel.
 The write methods of the resulting stream will throw an IllegalBlockingModeException if invoked while the underlying channel is in non-blocking mode. The stream will not be buffered. The stream will be safe for access by multiple concurrent threads. Closing the stream will in turn cause the channel to be closed. 
Params: ch – 
        The channel to which bytes will be written
Returns:  A new output stream/**
     * Constructs a stream that writes bytes to the given channel.
     *
     * <p> The {@code write} methods of the resulting stream will throw an
     * {@link IllegalBlockingModeException} if invoked while the underlying
     * channel is in non-blocking mode.  The stream will not be buffered.  The
     * stream will be safe for access by multiple concurrent threads.  Closing
     * the stream will in turn cause the channel to be closed.  </p>
     *
     * @param  ch
     *         The channel to which bytes will be written
     *
     * @return  A new output stream
     */
    public static OutputStream newOutputStream(WritableByteChannel ch) {
        Objects.requireNonNull(ch, "ch");

        return new OutputStream() {

            private ByteBuffer bb;
            private byte[] bs;       // Invoker's previous array
            private byte[] b1;

            @Override
            public synchronized void write(int b) throws IOException {
                if (b1 == null)
                    b1 = new byte[1];
                b1[0] = (byte) b;
                this.write(b1);
            }

            @Override
            public synchronized void write(byte[] bs, int off, int len)
                    throws IOException
            {
                if ((off < 0) || (off > bs.length) || (len < 0) ||
                    ((off + len) > bs.length) || ((off + len) < 0)) {
                    throw new IndexOutOfBoundsException();
                } else if (len == 0) {
                    return;
                }
                ByteBuffer bb = ((this.bs == bs)
                                 ? this.bb
                                 : ByteBuffer.wrap(bs));
                bb.limit(Math.min(off + len, bb.capacity()));
                bb.position(off);
                this.bb = bb;
                this.bs = bs;
                Channels.writeFully(ch, bb);
            }

            @Override
            public void close() throws IOException {
                ch.close();
            }

        };
    }

    Constructs a stream that reads bytes from the given channel.
 The stream will not be buffered, and it will not support the mark or reset methods. The stream will be safe for access by multiple concurrent threads. Closing the stream will in turn cause the channel to be closed. 
Params: ch – 
        The channel from which bytes will be read
Returns:  A new input stream
Since: 1.7/**
     * Constructs a stream that reads bytes from the given channel.
     *
     * <p> The stream will not be buffered, and it will not support the {@link
     * InputStream#mark mark} or {@link InputStream#reset reset} methods.  The
     * stream will be safe for access by multiple concurrent threads.  Closing
     * the stream will in turn cause the channel to be closed.  </p>
     *
     * @param  ch
     *         The channel from which bytes will be read
     *
     * @return  A new input stream
     *
     * @since 1.7
     */
    public static InputStream newInputStream(AsynchronousByteChannel ch) {
        Objects.requireNonNull(ch, "ch");
        return new InputStream() {

            private ByteBuffer bb;
            private byte[] bs;           // Invoker's previous array
            private byte[] b1;

            @Override
            public synchronized int read() throws IOException {
                if (b1 == null)
                    b1 = new byte[1];
                int n = this.read(b1);
                if (n == 1)
                    return b1[0] & 0xff;
                return -1;
            }

            @Override
            public synchronized int read(byte[] bs, int off, int len)
                    throws IOException
            {
                if ((off < 0) || (off > bs.length) || (len < 0) ||
                    ((off + len) > bs.length) || ((off + len) < 0)) {
                    throw new IndexOutOfBoundsException();
                } else if (len == 0) {
                    return 0;
                }

                ByteBuffer bb = ((this.bs == bs)
                                 ? this.bb
                                 : ByteBuffer.wrap(bs));
                bb.position(off);
                bb.limit(Math.min(off + len, bb.capacity()));
                this.bb = bb;
                this.bs = bs;

                boolean interrupted = false;
                try {
                    for (;;) {
                        try {
                            return ch.read(bb).get();
                        } catch (ExecutionException ee) {
                            throw new IOException(ee.getCause());
                        } catch (InterruptedException ie) {
                            interrupted = true;
                        }
                    }
                } finally {
                    if (interrupted)
                        Thread.currentThread().interrupt();
                }
            }

            @Override
            public void close() throws IOException {
                ch.close();
            }
        };
    }

    Constructs a stream that writes bytes to the given channel.
 The stream will not be buffered. The stream will be safe for access
by multiple concurrent threads.  Closing the stream will in turn cause
the channel to be closed.  
Params: ch – 
        The channel to which bytes will be written
Returns:  A new output stream
Since: 1.7/**
     * Constructs a stream that writes bytes to the given channel.
     *
     * <p> The stream will not be buffered. The stream will be safe for access
     * by multiple concurrent threads.  Closing the stream will in turn cause
     * the channel to be closed.  </p>
     *
     * @param  ch
     *         The channel to which bytes will be written
     *
     * @return  A new output stream
     *
     * @since 1.7
     */
    public static OutputStream newOutputStream(AsynchronousByteChannel ch) {
        Objects.requireNonNull(ch, "ch");
        return new OutputStream() {

            private ByteBuffer bb;
            private byte[] bs;   // Invoker's previous array
            private byte[] b1;

            @Override
            public synchronized void write(int b) throws IOException {
                if (b1 == null)
                    b1 = new byte[1];
                b1[0] = (byte) b;
                this.write(b1);
            }

            @Override
            public synchronized void write(byte[] bs, int off, int len)
                    throws IOException
            {
                if ((off < 0) || (off > bs.length) || (len < 0) ||
                    ((off + len) > bs.length) || ((off + len) < 0)) {
                    throw new IndexOutOfBoundsException();
                } else if (len == 0) {
                    return;
                }
                ByteBuffer bb = ((this.bs == bs)
                                 ? this.bb
                                 : ByteBuffer.wrap(bs));
                bb.limit(Math.min(off + len, bb.capacity()));
                bb.position(off);
                this.bb = bb;
                this.bs = bs;

                boolean interrupted = false;
                try {
                    while (bb.remaining() > 0) {
                        try {
                            ch.write(bb).get();
                        } catch (ExecutionException ee) {
                            throw new IOException(ee.getCause());
                        } catch (InterruptedException ie) {
                            interrupted = true;
                        }
                    }
                } finally {
                    if (interrupted)
                        Thread.currentThread().interrupt();
                }
            }

            @Override
            public void close() throws IOException {
                ch.close();
            }
        };
    }


    // -- Channels from streams --

    Constructs a channel that reads bytes from the given stream.
 The resulting channel will not be buffered; it will simply redirect
its I/O operations to the given stream.  Closing the channel will in
turn cause the stream to be closed.  
Params: in – 
        The stream from which bytes are to be read
Returns:  A new readable byte channel/**
     * Constructs a channel that reads bytes from the given stream.
     *
     * <p> The resulting channel will not be buffered; it will simply redirect
     * its I/O operations to the given stream.  Closing the channel will in
     * turn cause the stream to be closed.  </p>
     *
     * @param  in
     *         The stream from which bytes are to be read
     *
     * @return  A new readable byte channel
     */
    public static ReadableByteChannel newChannel(InputStream in) {
        Objects.requireNonNull(in, "in");

        if (in.getClass() == FileInputStream.class) {
            return ((FileInputStream) in).getChannel();
        }

        return new ReadableByteChannelImpl(in);
    }

    private static class ReadableByteChannelImpl
        extends AbstractInterruptibleChannel    // Not really interruptible
        implements ReadableByteChannel
    {
        private final InputStream in;
        private static final int TRANSFER_SIZE = 8192;
        private byte[] buf = new byte[0];
        private final Object readLock = new Object();

        ReadableByteChannelImpl(InputStream in) {
            this.in = in;
        }

        @Override
        public int read(ByteBuffer dst) throws IOException {
            if (!isOpen()) {
                throw new ClosedChannelException();
            }

            int len = dst.remaining();
            int totalRead = 0;
            int bytesRead = 0;
            synchronized (readLock) {
                while (totalRead < len) {
                    int bytesToRead = Math.min((len - totalRead),
                                               TRANSFER_SIZE);
                    if (buf.length < bytesToRead)
                        buf = new byte[bytesToRead];
                    if ((totalRead > 0) && !(in.available() > 0))
                        break; // block at most once
                    try {
                        begin();
                        bytesRead = in.read(buf, 0, bytesToRead);
                    } finally {
                        end(bytesRead > 0);
                    }
                    if (bytesRead < 0)
                        break;
                    else
                        totalRead += bytesRead;
                    dst.put(buf, 0, bytesRead);
                }
                if ((bytesRead < 0) && (totalRead == 0))
                    return -1;

                return totalRead;
            }
        }

        @Override
        protected void implCloseChannel() throws IOException {
            in.close();
        }
    }


    Constructs a channel that writes bytes to the given stream.
 The resulting channel will not be buffered; it will simply redirect
its I/O operations to the given stream.  Closing the channel will in
turn cause the stream to be closed.  
Params: out – 
        The stream to which bytes are to be written
Returns:  A new writable byte channel/**
     * Constructs a channel that writes bytes to the given stream.
     *
     * <p> The resulting channel will not be buffered; it will simply redirect
     * its I/O operations to the given stream.  Closing the channel will in
     * turn cause the stream to be closed.  </p>
     *
     * @param  out
     *         The stream to which bytes are to be written
     *
     * @return  A new writable byte channel
     */
    public static WritableByteChannel newChannel(OutputStream out) {
        Objects.requireNonNull(out, "out");

        if (out.getClass() == FileOutputStream.class) {
            return ((FileOutputStream) out).getChannel();
        }

        return new WritableByteChannelImpl(out);
    }

    private static class WritableByteChannelImpl
        extends AbstractInterruptibleChannel    // Not really interruptible
        implements WritableByteChannel
    {
        private final OutputStream out;
        private static final int TRANSFER_SIZE = 8192;
        private byte[] buf = new byte[0];
        private final Object writeLock = new Object();

        WritableByteChannelImpl(OutputStream out) {
            this.out = out;
        }

        @Override
        public int write(ByteBuffer src) throws IOException {
            if (!isOpen()) {
                throw new ClosedChannelException();
            }

            int len = src.remaining();
            int totalWritten = 0;
            synchronized (writeLock) {
                while (totalWritten < len) {
                    int bytesToWrite = Math.min((len - totalWritten),
                                                TRANSFER_SIZE);
                    if (buf.length < bytesToWrite)
                        buf = new byte[bytesToWrite];
                    src.get(buf, 0, bytesToWrite);
                    try {
                        begin();
                        out.write(buf, 0, bytesToWrite);
                    } finally {
                        end(bytesToWrite > 0);
                    }
                    totalWritten += bytesToWrite;
                }
                return totalWritten;
            }
        }

        @Override
        protected void implCloseChannel() throws IOException {
            out.close();
        }
    }


    // -- Character streams from channels --

    Constructs a reader that decodes bytes from the given channel using the
given decoder.
 The resulting stream will contain an internal input buffer of at least minBufferCap bytes. The stream's read methods will, as needed, fill the buffer by reading bytes from the underlying channel; if the channel is in non-blocking mode when bytes are to be read then an IllegalBlockingModeException will be thrown. The resulting stream will not otherwise be buffered, and it will not support the mark or reset methods. Closing the stream will in turn cause the channel to be closed. 
Params: ch – 
        The channel from which bytes will be read
dec – 
        The charset decoder to be used
minBufferCap –  The minimum capacity of the internal byte buffer, or -1 if an implementation-dependent default capacity is to be used
Returns:  A new reader/**
     * Constructs a reader that decodes bytes from the given channel using the
     * given decoder.
     *
     * <p> The resulting stream will contain an internal input buffer of at
     * least {@code minBufferCap} bytes.  The stream's {@code read} methods
     * will, as needed, fill the buffer by reading bytes from the underlying
     * channel; if the channel is in non-blocking mode when bytes are to be
     * read then an {@link IllegalBlockingModeException} will be thrown.  The
     * resulting stream will not otherwise be buffered, and it will not support
     * the {@link Reader#mark mark} or {@link Reader#reset reset} methods.
     * Closing the stream will in turn cause the channel to be closed.  </p>
     *
     * @param  ch
     *         The channel from which bytes will be read
     *
     * @param  dec
     *         The charset decoder to be used
     *
     * @param  minBufferCap
     *         The minimum capacity of the internal byte buffer,
     *         or {@code -1} if an implementation-dependent
     *         default capacity is to be used
     *
     * @return  A new reader
     */
    public static Reader newReader(ReadableByteChannel ch,
                                   CharsetDecoder dec,
                                   int minBufferCap)
    {
        Objects.requireNonNull(ch, "ch");
        return StreamDecoder.forDecoder(ch, dec.reset(), minBufferCap);
    }

    Constructs a reader that decodes bytes from the given channel according
to the named charset.
 An invocation of this method of the form
 
    Channels.newReader(ch, csname)
 
behaves in exactly the same way as the expression
 
    Channels.newReader(ch, Charset.forName(csName))
 
Params: ch – 
        The channel from which bytes will be read
csName – 
        The name of the charset to be used
Throws: UnsupportedCharsetException – 
         If no support for the named charset is available
         in this instance of the Java virtual machine
Returns:  A new reader/**
     * Constructs a reader that decodes bytes from the given channel according
     * to the named charset.
     *
     * <p> An invocation of this method of the form
     *
     * <pre> {@code
     *     Channels.newReader(ch, csname)
     * } </pre>
     *
     * behaves in exactly the same way as the expression
     *
     * <pre> {@code
     *     Channels.newReader(ch, Charset.forName(csName))
     * } </pre>
     *
     * @param  ch
     *         The channel from which bytes will be read
     *
     * @param  csName
     *         The name of the charset to be used
     *
     * @return  A new reader
     *
     * @throws  UnsupportedCharsetException
     *          If no support for the named charset is available
     *          in this instance of the Java virtual machine
     */
    public static Reader newReader(ReadableByteChannel ch,
                                   String csName)
    {
        Objects.requireNonNull(csName, "csName");
        return newReader(ch, Charset.forName(csName).newDecoder(), -1);
    }

    Constructs a reader that decodes bytes from the given channel according
to the given charset.
 An invocation of this method of the form
 
    Channels.newReader(ch, charset)
 
behaves in exactly the same way as the expression
 
    Channels.newReader(ch, Charset.forName(csName).newDecoder(), -1)
 
 The reader's default action for malformed-input and unmappable-character errors is to report them. When more control over the error handling is required, the constructor that takes a CharsetDecoder should be used. 
Params: ch – The channel from which bytes will be read
charset – The charset to be used
Returns:  A new reader/**
     * Constructs a reader that decodes bytes from the given channel according
     * to the given charset.
     *
     * <p> An invocation of this method of the form
     *
     * <pre> {@code
     *     Channels.newReader(ch, charset)
     * } </pre>
     *
     * behaves in exactly the same way as the expression
     *
     * <pre> {@code
     *     Channels.newReader(ch, Charset.forName(csName).newDecoder(), -1)
     * } </pre>
     *
     * <p> The reader's default action for malformed-input and unmappable-character
     * errors is to {@linkplain java.nio.charset.CodingErrorAction#REPORT report}
     * them. When more control over the error handling is required, the constructor
     * that takes a {@linkplain java.nio.charset.CharsetDecoder} should be used.
     *
     * @param  ch The channel from which bytes will be read
     *
     * @param  charset The charset to be used
     *
     * @return  A new reader
     */
    public static Reader newReader(ReadableByteChannel ch, Charset charset) {
        Objects.requireNonNull(charset, "charset");
        return newReader(ch, charset.newDecoder(), -1);
    }

    Constructs a writer that encodes characters using the given encoder and
writes the resulting bytes to the given channel.
 The resulting stream will contain an internal output buffer of at least minBufferCap bytes. The stream's write methods will, as needed, flush the buffer by writing bytes to the underlying channel; if the channel is in non-blocking mode when bytes are to be written then an IllegalBlockingModeException will be thrown. The resulting stream will not otherwise be buffered. Closing the stream will in turn cause the channel to be closed. 
Params: ch – 
        The channel to which bytes will be written
enc – 
        The charset encoder to be used
minBufferCap –  The minimum capacity of the internal byte buffer, or -1 if an implementation-dependent default capacity is to be used
Returns:  A new writer/**
     * Constructs a writer that encodes characters using the given encoder and
     * writes the resulting bytes to the given channel.
     *
     * <p> The resulting stream will contain an internal output buffer of at
     * least {@code minBufferCap} bytes.  The stream's {@code write} methods
     * will, as needed, flush the buffer by writing bytes to the underlying
     * channel; if the channel is in non-blocking mode when bytes are to be
     * written then an {@link IllegalBlockingModeException} will be thrown.
     * The resulting stream will not otherwise be buffered.  Closing the stream
     * will in turn cause the channel to be closed.  </p>
     *
     * @param  ch
     *         The channel to which bytes will be written
     *
     * @param  enc
     *         The charset encoder to be used
     *
     * @param  minBufferCap
     *         The minimum capacity of the internal byte buffer,
     *         or {@code -1} if an implementation-dependent
     *         default capacity is to be used
     *
     * @return  A new writer
     */
    public static Writer newWriter(WritableByteChannel ch,
                                   CharsetEncoder enc,
                                   int minBufferCap)
    {
        Objects.requireNonNull(ch, "ch");
        return StreamEncoder.forEncoder(ch, enc.reset(), minBufferCap);
    }

    Constructs a writer that encodes characters according to the named
charset and writes the resulting bytes to the given channel.
 An invocation of this method of the form
 
    Channels.newWriter(ch, csname)
 
behaves in exactly the same way as the expression
 
    Channels.newWriter(ch, Charset.forName(csName))
 
Params: ch – 
        The channel to which bytes will be written
csName – 
        The name of the charset to be used
Throws: UnsupportedCharsetException – 
         If no support for the named charset is available
         in this instance of the Java virtual machine
Returns:  A new writer/**
     * Constructs a writer that encodes characters according to the named
     * charset and writes the resulting bytes to the given channel.
     *
     * <p> An invocation of this method of the form
     *
     * <pre> {@code
     *     Channels.newWriter(ch, csname)
     * } </pre>
     *
     * behaves in exactly the same way as the expression
     *
     * <pre> {@code
     *     Channels.newWriter(ch, Charset.forName(csName))
     * } </pre>
     *
     * @param  ch
     *         The channel to which bytes will be written
     *
     * @param  csName
     *         The name of the charset to be used
     *
     * @return  A new writer
     *
     * @throws  UnsupportedCharsetException
     *          If no support for the named charset is available
     *          in this instance of the Java virtual machine
     */
    public static Writer newWriter(WritableByteChannel ch,
                                   String csName)
    {
        Objects.requireNonNull(csName, "csName");
        return newWriter(ch, Charset.forName(csName).newEncoder(), -1);
    }

    Constructs a writer that encodes characters according to the given
charset and writes the resulting bytes to the given channel.
 An invocation of this method of the form
 
    Channels.newWriter(ch, charset)
 
behaves in exactly the same way as the expression
 
    Channels.newWriter(ch, Charset.forName(csName).newEncoder(), -1)
 
 The writer's default action for malformed-input and unmappable-character errors is to report them. When more control over the error handling is required, the constructor that takes a CharsetEncoder should be used. 
Params: ch – 
        The channel to which bytes will be written
charset – 
        The charset to be used
Returns:  A new writer/**
     * Constructs a writer that encodes characters according to the given
     * charset and writes the resulting bytes to the given channel.
     *
     * <p> An invocation of this method of the form
     *
     * <pre> {@code
     *     Channels.newWriter(ch, charset)
     * } </pre>
     *
     * behaves in exactly the same way as the expression
     *
     * <pre> {@code
     *     Channels.newWriter(ch, Charset.forName(csName).newEncoder(), -1)
     * } </pre>
     *
     * <p> The writer's default action for malformed-input and unmappable-character
     * errors is to {@linkplain java.nio.charset.CodingErrorAction#REPORT report}
     * them. When more control over the error handling is required, the constructor
     * that takes a {@linkplain java.nio.charset.CharsetEncoder} should be used.
     *
     * @param  ch
     *         The channel to which bytes will be written
     *
     * @param  charset
     *         The charset to be used
     *
     * @return  A new writer
     */
    public static Writer newWriter(WritableByteChannel ch, Charset charset) {
        Objects.requireNonNull(charset, "charset");
        return newWriter(ch, charset.newEncoder(), -1);
}
}
Author:	Mark Reinhold, Mike McCloskey, JSR-51 Expert Group
Since:	1.4
Params:	ch – The channel from which bytes will be read
Returns:	A new input stream
Params:	ch – The channel to which bytes will be written
Returns:	A new output stream
Params:	in – The stream from which bytes are to be read
Returns:	A new readable byte channel
Params:	out – The stream to which bytes are to be written
Returns:	A new writable byte channel
Params:	ch – The channel from which bytes will be read csName – The name of the charset to be used
Throws:	UnsupportedCharsetException – If no support for the named charset is available in this instance of the Java virtual machine
Returns:	A new reader
/

java/ 12/ java.base/java/nio/channels/Channels.java
