通道(Channel)的原理与获取

package com.aff.nio;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.FileChannel.MapMode;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

import org.junit.Test;

/*
 * 1.通道（channel）：用于源节点于目标节点的连接，在Java NIO中负责缓冲区数据的传输。
 * channel本身不存储数据的，因此需要配合缓冲区传输‘
 * 2.通道的主要实现类
 *  java.nio.channels.Channel接口
 *     |FileChannel    本地的文件通道
 *     |SocketChannel   网络 TCP
 *     |ServerSocketChannel  网络TCP
 *     |DatagramChannel    网络 UDP
 *  
 * 3.获取通道
 *       ①.java针对支持通道的类提供了getChannel()方法
 *  
 *                 本地：
 *                       FileInputStream/FileOutputStream
 *                       RandomAccessFile//随机存储文件流
 *  
 *                 网络IO：
 *                       Socket
 *                       ServerSocket
 *                       DatagremSocket
 *  
 *       ②.jdk1.7NIO.2针对各个通道提供静态方法open()
 *       ③.jdk1.7中的NIO.2的Files工具类的newByteChannel()
 *  
 */
public class TestChannel {

    // 通道之间的数据传输(直接缓冲区)
    @Test
    public void test3() throws IOException {
        FileChannel inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
        FileChannel outChannel = FileChannel.open(Paths.get("4.jpg"), StandardOpenOption.WRITE, StandardOpenOption.READ,
                StandardOpenOption.CREATE);
        inChannel.transferTo(0, inChannel.size(), outChannel);// 从inchannel来到outchannel中去
        // inChannel.transferTo(position, count, target)
        // outChannel.transferFrom(inChannel, 0, inChannel.size());
        // outChannel.transferFrom(src, position, count)

    }

    // 使用直接缓冲区完成文件的复制(内存映射文件的方)
    @Test
    public void test2() throws Exception {
        long start = System.currentTimeMillis();

        FileChannel inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
        FileChannel outChannel = FileChannel.open(Paths.get("3.jpg"), StandardOpenOption.WRITE, StandardOpenOption.READ,
                StandardOpenOption.CREATE);
        // 内存映射文件
        MappedByteBuffer inMappedByteBuffer = inChannel.map(MapMode.READ_ONLY, 0, inChannel.size());
        MappedByteBuffer outMappedByteBuffer = outChannel.map(MapMode.READ_WRITE, 0, inChannel.size());
        // 直接对缓冲区进行数据的读写操作
        byte[] dst = new byte[inMappedByteBuffer.limit()];
        inMappedByteBuffer.get(dst);
        outMappedByteBuffer.put(dst);
        inChannel.close();
        outChannel.close();

        long end = System.currentTimeMillis();
        System.out.println("时间为：" + (end - start));// 7
    }

    // 使用通道完成文件的复制（非直接缓冲区）
    @Test
    public void test1() throws FileNotFoundException {

        long start = System.currentTimeMillis();
        FileInputStream fis = null;
        FileOutputStream fos = null;
        FileChannel inchannel = null;
        FileChannel outchannel = null;
        try {
            fis = new FileInputStream("1.jpg");
            fos = new FileOutputStream("2.jpg");

            // 1.获取通道
            inchannel = fis.getChannel();
            outchannel = fos.getChannel();
            // 2.分配指定大小的缓冲区
            ByteBuffer buf = ByteBuffer.allocate(1024);
            // 3.将通道中的数据存入缓冲区中
            while ((inchannel.read(buf)) != -1) {
                buf.flip(); // 然后切换成读取模式，再输出
                // 4.将缓冲区的数据写入通道中
                outchannel.write(buf);
                buf.clear();// 清空缓冲区
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (outchannel != null) {
                try {
                    outchannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (inchannel != null) {
                try {
                    inchannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        long end = System.currentTimeMillis();
        System.out.println("时间为：" + (end - start));// 146
    }

}