本地文件写数据,如果没有文件创建文件 

/**
 * 使用ByteBuffer(缓冲)和FileChannel(通道),将Hello NIO写入到file01.txt文件中
 * 如果文件不存在创建文件
 * @author hrui
 * @date 2024/7/27 22:27
 */
public class NIOFileChannel01 {
    public static void main(String[] args) throws IOException {
        String str = "Hello NIO";
        //1.创建一个输出流(Channel还是通过输入输出流创建)
        FileOutputStream fileOutputStream = new FileOutputStream("D:\\file01.txt");

        //2.通过fileOutputStream获取对应的FileChannel
        //这个fileChannel对象的真实类型是FileChannelImpl
        FileChannel fileChannel = fileOutputStream.getChannel();

        //3.创建一个缓冲区(ByteBuffer)
        ByteBuffer byteBuffer = ByteBuffer.allocate(1024);

        //4.将str放入到ByteBuffer
        byteBuffer.put(str.getBytes());

        //5.将byteBuffer的指针复位
        byteBuffer.flip();

        //6.将byteBuffer的数据写入到fileChannel
        fileChannel.write(byteBuffer);
        fileOutputStream.close();
    }
}

从本地文件读数据

/**
 * 本地文件读数据
 * @author hrui
 * @date 2024/7/28 7:50
 */
public class NIOFileChannel02 {
    public static void main(String[] args) throws IOException {
        //创建文件的输入流
        File file = new File("D:\\file01.txt");
        FileInputStream fileInputStream = new FileInputStream(file);

        //通过fileInputStream 获取对应的FileChannel
        FileChannel fileChannel = fileInputStream.getChannel();

        //创建缓冲区
        ByteBuffer byteBuffer = ByteBuffer.allocate((int) file.length());

        //将通道的数据读入到缓冲区
        fileChannel.read(byteBuffer);

        //将缓冲区的数据转成字符串
        System.out.println(new String(byteBuffer.array()));
        fileInputStream.close();
    }
}

文件拷贝

package org.example.demo;

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

/**
 * 使用一个Buffer完成文件拷贝
 * 将D盘目录下的1.txt(随便写点内容)拷贝到2.txt
 * @author hrui
 * @date 2024/7/28 8:14
 */
public class NIOFileChannel03 {
    public static void main(String[] args) throws IOException {
        // 创建一个输入流 读文件
        FileInputStream fileInputStream = new FileInputStream("D://1.txt");
        FileChannel channel01 = fileInputStream.getChannel();

        // 创建一个输出流 写文件
        FileOutputStream fileOutputStream = new FileOutputStream("D://2.txt");
        FileChannel channel02 = fileOutputStream.getChannel();

        ByteBuffer allocate = ByteBuffer.allocate(5);

        //循环读取
        while(true){
            //这里有个重要的操作,不要忘记
            allocate.clear();

            // 从通道读取512字节数据放入ByteBuffer
            int read = channel01.read(allocate);
            if (read == -1){//如果读到-1说明读完了
                break;
            }
            //没有读完 将buffer已经有的数据直接写入到channel02
            allocate.flip();//切换模式
            channel02.write(allocate);

        }
        //关闭通道
        channel01.close();
        channel02.close();
        //关闭流
        fileInputStream.close();
        fileOutputStream.close();

    }
}

拷贝的另外一种方式

把D盘一张图片进行拷贝 例如 1.PNG  ----->   2.PNG

package org.example.demo;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

/**
 * @author hrui
 * @date 2024/7/28 9:30
 */
public class NIOFileChannel04 {

    public static void main(String[] args) throws IOException {
        //创建相关流
        FileInputStream fileInputStream = new FileInputStream("3.jpg");
        FileOutputStream fileOutputStream = new FileOutputStream("4.jpg");

        //创建相关通道
        FileChannel channel01 = fileInputStream.getChannel();
        FileChannel channel02 = fileOutputStream.getChannel();

        //使用transferFrom完成传输(拷贝)
        channel02.transferFrom(channel01, 0, channel01.size());

        //关闭相关通道和流
        channel01.close();
        channel02.close();
        fileInputStream.close();
        fileOutputStream.close();
    }
}