ScatteringByteChannel.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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package java.nio.channels;

import java.io.IOException;
import java.nio.ByteBuffer;

/**
 * A channel that can read bytes into a sequence of buffers.
 *
 * <p> A <i>scattering</i> read operation reads, in a single invocation, a
 * sequence of bytes into one or more of a given sequence of buffers.
 * Scattering reads are often useful when implementing network protocols or
 * file formats that, for example, group data into segments consisting of one
 * or more fixed-length headers followed by a variable-length body.  Similar
 * <i>gathering</i> write operations are defined in the {@link
 * GatheringByteChannel} interface.  </p>
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */
// 散射通道，可将单个通道的内容发送到多个缓存区。例如支持将文件中的内容批量读取到多个缓冲区
public interface ScatteringByteChannel extends ReadableByteChannel {
    
    /**
     * Reads a sequence of bytes from this channel into a subsequence of the
     * given buffers.
     *
     * <p> An invocation of this method attempts to read up to <i>r</i> bytes
     * from this channel, where <i>r</i> is the total number of bytes remaining
     * the specified subsequence of the given buffer array, that is,
     *
     * <blockquote><pre>
     * dsts[offset].remaining()
     *     + dsts[offset+1].remaining()
     *     + ... + dsts[offset+length-1].remaining()</pre></blockquote>
     *
     * at the moment that this method is invoked.
     *
     * <p> Suppose that a byte sequence of length <i>n</i> is read, where
     * {@code 0}&nbsp;{@code <=}&nbsp;<i>n</i>&nbsp;{@code <=}&nbsp;<i>r</i>.
     * Up to the first {@code dsts[offset].remaining()} bytes of this sequence
     * are transferred into buffer {@code dsts[offset]}, up to the next
     * {@code dsts[offset+1].remaining()} bytes are transferred into buffer
     * {@code dsts[offset+1]}, and so forth, until the entire byte sequence
     * is transferred into the given buffers.  As many bytes as possible are
     * transferred into each buffer, hence the final position of each updated
     * buffer, except the last updated buffer, is guaranteed to be equal to
     * that buffer's limit.
     *
     * <p> This method may be invoked at any time.  If another thread has
     * already initiated a read operation upon this channel, however, then an
     * invocation of this method will block until the first operation is
     * complete. </p>
     *
     * @param dsts   The buffers into which bytes are to be transferred
     * @param offset The offset within the buffer array of the first buffer into
     *               which bytes are to be transferred; must be non-negative and no
     *               larger than {@code dsts.length}
     * @param length The maximum number of buffers to be accessed; must be
     *               non-negative and no larger than
     *               {@code dsts.length}&nbsp;-&nbsp;{@code offset}
     *
     * @return The number of bytes read, possibly zero,
     * or {@code -1} if the channel has reached end-of-stream
     *
     * @throws IndexOutOfBoundsException   If the preconditions on the {@code offset} and {@code length}
     *                                     parameters do not hold
     * @throws NonReadableChannelException If this channel was not opened for reading
     * @throws ClosedChannelException      If this channel is closed
     * @throws AsynchronousCloseException  If another thread closes this channel
     *                                     while the read operation is in progress
     * @throws ClosedByInterruptException  If another thread interrupts the current thread
     *                                     while the read operation is in progress, thereby
     *                                     closing the channel and setting the current thread's
     *                                     interrupt status
     * @throws IOException                 If some other I/O error occurs
     */
    /*
     * 从当前通道中读取数据，读到的内容依次存入dsts中offset处起的length个缓冲区
     * 该方法是一次性地，即已经读完的流不可以重复读取
     */
    long read(ByteBuffer[] dsts, int offset, int length) throws IOException;
    
    /**
     * Reads a sequence of bytes from this channel into the given buffers.
     *
     * <p> An invocation of this method of the form {@code c.read(dsts)}
     * behaves in exactly the same manner as the invocation
     *
     * <blockquote><pre>
     * c.read(dsts, 0, dsts.length);</pre></blockquote>
     *
     * @param dsts The buffers into which bytes are to be transferred
     *
     * @return The number of bytes read, possibly zero,
     * or {@code -1} if the channel has reached end-of-stream
     *
     * @throws NonReadableChannelException If this channel was not opened for reading
     * @throws ClosedChannelException      If this channel is closed
     * @throws AsynchronousCloseException  If another thread closes this channel
     *                                     while the read operation is in progress
     * @throws ClosedByInterruptException  If another thread interrupts the current thread
     *                                     while the read operation is in progress, thereby
     *                                     closing the channel and setting the current thread's
     *                                     interrupt status
     * @throws IOException                 If some other I/O error occurs
     */
    /*
     * 从当前通道中读取数据，读到的内容依次存入dsts中的各个缓冲区
     * 该方法是一次性地，即已经读完的流不可以重复读取
     */
    long read(ByteBuffer[] dsts) throws IOException;
    
}