NIO_通道的数据传输与内存映射文件

package com.young.nio.day01;

import org.junit.Test;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

/**
 * 一、通道(Channel):用于原节点与目标节点的连接。在Java NIO中负责缓冲区中数据的传输。Channel本身不存储数据,因此需要配合缓冲区进行传输。
 *
 * 二、通道的主要实现类
 * java.nio.channels.Channel接口:
 *  |--FileChannel
 *  |--SocketChannel
 *  |--ServerSocketChannel
 *  |--DatagramChannel
 *
 * 三、获取通道
 * 1.Java针对支持通道的类提供了getChannel()方法
 *      本地IO:
 *      FileInputStream/FileOutputStream
 *      RandomAccessFile
 *
 *      网络IO:
 *      Socket
 *      ServerSocket
 *      DatagramSocket
 *
 * 2.在JDK1.7中的NIO2针对各个通道提供了静态方法open()
 *
 * 3.在JDK1.7中的NIO2的Files工具类的newByteChannel()
 *
 * 四、通道之间的数据传输
 * transferFrom()
 * transferTo()
 */
public class TestChannel {

    //通道之间的数据传输(直接缓冲区)
    @Test
    public void test3() {
        FileChannel inChannel = null;
        FileChannel outChannel = null;
        try {
            inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
            outChannel = FileChannel.open(Paths.get("4.jpg"), StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE);

            //inChannel.transferTo(0,inChannel.size(),outChannel);
            outChannel.transferFrom(inChannel, 0, inChannel.size());
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inChannel != null) {
                try {
                    inChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (outChannel != null) {
                try {
                    outChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

    //使用直接缓冲区完成文件的复制(内存映射文件)
    @Test
    public void test2() {
        FileChannel inChannel = null;
        FileChannel outChannel = null;
        try {
            inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
            outChannel = FileChannel.open(Paths.get("3.jpg"), StandardOpenOption.READ, StandardOpenOption.WRITE, StandardOpenOption.CREATE);

            //内存映射文件
            MappedByteBuffer inMappedBuffer = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());
            MappedByteBuffer outMappedBuffer = outChannel.map(FileChannel.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[inMappedBuffer.limit()];
            inMappedBuffer.get(dst);
            outMappedBuffer.put(dst);
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inChannel != null) {
                try {
                    inChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (outChannel != null) {
                try {
                    outChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }


    //利用通道文件的复制(非直接缓冲区)
    @Test
    public void test1() {
        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();//切换成读取数据的模式
                //4.将缓冲区中的数据写入通道中
                outChannel.write(buf);
                buf.clear();//清空缓冲区
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (outChannel != null) {
                    outChannel.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (inChannel != null) {
                    inChannel.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (fos != null) {
                    fos.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                if (fis != null) {
                    fis.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

    }

}