public static void main(String[] args) throws IOException {
        // 这里的"rw"是指支持读和写
        RandomAccessFile randomAccessFile = new RandomAccessFile("C:\\Users\\Administrator\\Desktop\\data.txt","rw");
        FileChannel fileChannel = randomAccessFile.getChannel();
        // 读取文件内容：
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        int num = fileChannel.read(buffer);
        System.out.println("读取的数据量：" + num + "，内容为：\r\n" + new String(buffer.array()));
        buffer.clear();
        // 向文件内追加内容：祝源码班各位大帅比迎娶白富美！
        buffer.put("\r\n".getBytes());
        buffer.put("祝源码班各位大帅比迎娶白富美！".getBytes());
        buffer.flip();
        while(buffer.hasRemaining()) {
            // 将 Buffer 中的内容写入文件
            fileChannel.write(buffer);
        }
    }

FileChannel 本地文件读写

一个Buffer写,一个Buffer读

//本地文件写数据
public static void main(String[] args) throws Exception{
    String str = "hello";
    //创建一个输出流->channel
    FileOutputStream fileOutputStream = new FileOutputStream("d:\\file01.txt");
    //通过 fileOutputStream 获取 对应的 FileChannel
    //这个 fileChannel 真实 类型是  FileChannelImpl
    FileChannel fileChannel = fileOutputStream.getChannel();
    //创建一个缓冲区 ByteBuffer
    ByteBuffer byteBuffer = ByteBuffer.allocate(1024);
    //将 str 放入 byteBuffer
    byteBuffer.put(str.getBytes()); 
    //对byteBuffer 进行flip
    byteBuffer.flip();
    //将byteBuffer 数据写入到 fileChannel
    fileChannel.write(byteBuffer);
    fileOutputStream.close();
}
//本地文件读数据
public static void main(String[] args) throws Exception {
    //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 -> 实际类型  FileChannelImpl
    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Buffer
    fileChannel.read(byteBuffer);
    //将byteBuffer 的 字节数据 转成String
    System.out.println(new String(byteBuffer.array()));
    fileInputStream.close();
}

一个Buffer读写文件

//使用一个Buffer完成文件读取
public static void main(String[] args) throws Exception {
    FileInputStream fileInputStream = new FileInputStream("1.txt");
    FileChannel fileChannel01 = fileInputStream.getChannel();
    FileOutputStream fileOutputStream = new FileOutputStream("2.txt");
    FileChannel fileChannel02 = fileOutputStream.getChannel();
    ByteBuffer byteBuffer = ByteBuffer.allocate(512);
    while (true) { //循环读取
        //这里有一个重要的操作，一定不要忘了
        /*
         public final Buffer clear() {
            position = 0;
            limit = capacity;
            mark = -1;
            return this;
        }
         */
        byteBuffer.clear(); //清空buffer
        int read = fileChannel01.read(byteBuffer);
        System.out.println("read =" + read);
        if(read == -1) { //表示读完
            break;
        }
        //将buffer 中的数据写入到 fileChannel02 -- 2.txt
        byteBuffer.flip();
        fileChannel02.write(byteBuffer);
    }
    //关闭相关的流
    fileInputStream.close();
    fileOutputStream.close();
}

拷贝文件

transferFrom

//拷贝文件transferFrom 方法
public static void main(String[] args)  throws Exception {
    //创建相关流
    FileInputStream fileInputStream = new FileInputStream("d:\\a.jpg");
    FileOutputStream fileOutputStream = new FileOutputStream("d:\\a2.jpg");
    //获取各个流对应的filechannel
    FileChannel sourceCh = fileInputStream.getChannel();
    FileChannel destCh = fileOutputStream.getChannel();
    //使用transferForm完成拷贝
    destCh.transferFrom(sourceCh,0,sourceCh.size());
    //关闭相关通道和流
    sourceCh.close();
    destCh.close();
    fileInputStream.close();
    fileOutputStream.close();
}

transferTo

超过 2g 大小的文件传输

public class TestFileChannelTransferTo {
    public static void main(String[] args) {
        try (
                FileChannel from = new FileInputStream("data.txt").getChannel();
                FileChannel to = new FileOutputStream("to.txt").getChannel();
        ) {
            // 效率高，底层会利用操作系统的零拷贝进行优化, 2g 数据
            long size = from.size();
            // left 变量代表还剩余多少字节
            for (long left = size; left > 0; ) {
                System.out.println("position:" + (size - left) + " left:" + left);
                left -= from.transferTo((size - left), left, to);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}