用FileChannel和Buffer操作本地文件

Netty学习之通道Channel和缓冲区Buffer

package com.huangz.demo.nio;
import io.netty.buffer.ByteBuf;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

/**
 * 利用FileChannel通道和Buffer缓存区向本地磁盘写一个文件
 */
public class NIOFileChannel {
    public static void main(String[] args) throws Exception {
        //向本地文件写数据
        //writeFile();
        //从本地文件读数据
        //readFile();
        //文件复制
        copyFile();
    }

    /**
     * 用FileChannel通道和Buffer缓冲区向本地文件写数据
     */
    private static void writeFile() throws Exception{
        //创建一个输出流
        FileOutputStream fileOutputStream = new FileOutputStream("d:\file01.txt");
        //通过文件输出流，获取对应的通道
        FileChannel fileChannel = fileOutputStream.getChannel();
        //创建一个缓冲区
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
        String str ="Netty必知必会";
        byteBuffer.put(str.getBytes());
        //flip前：position= 17，limit=1024
        //从写转换为读，flip反转，这一步发生了什么？ position和limit值的变化
        byteBuffer.flip();
        //flip后：position= 0，limit=17
        //将缓冲区数据写入到通道
        fileChannel.write(byteBuffer);
        //关闭流
        fileOutputStream.close();
        System.out.println("写入文件完成...");
    }
    /**
     * 用FileChannel通道和Buffer缓冲区从本地文件读数据
     */
    private static void readFile() throws Exception {
        System.out.println("开始读取数据....");
        //创建文件的输入流
        File file = new File ("D:\file01.txt");
        FileInputStream fileInputStream = new FileInputStream(file);
        //获取通道
        FileChannel fileChannel = fileInputStream.getChannel();
        //创建缓冲区
        int length = (int)file.length();
        ByteBuffer byteBuffer = ByteBuffer.allocate(length);
        //将读取通道数据到缓冲区
        fileChannel.read(byteBuffer);
        //从缓冲区中取数据
        byte[] bytes = byteBuffer.array();
        fileInputStream.close();
        System.out.println(new String(bytes));

    }

    /**
     * 文件拷贝
     * @throws Exception
     */
    private static void  copyFile() throws Exception {
        //读文件 创建输入流
        FileInputStream fileInputStream = new FileInputStream("1.txt");
        FileChannel channel01 = fileInputStream.getChannel();
        //写文件 创建输出流
        FileOutputStream fileOutputStream = new FileOutputStream("2.txt");
        FileChannel channel02 = fileOutputStream.getChannel();

        //创建一个Buffer
        ByteBuffer byteBuffer =ByteBuffer.allocate(10);
        while (true){
            //从通道读取数据
            byteBuffer.clear();
            int read = channel01.read(byteBuffer);
            if(read==-1){
                break;
            }
            //读写转换
            byteBuffer.flip();
            //将读取到的数据，写入到2.txt
            channel02.write(byteBuffer);
        }
        fileInputStream.close();
        fileOutputStream.close();
        System.out.println("复制文件完成");
    }
}