NIO例子

public class Main3 {
    

    /** * nio读取文件中的数据 * @param args */
    public static void main(String[] args) throws IOException {
    
        readThenWrite();
    }


    /** * nio读取文件中的数据 * 文件 -> channel -> buffer * @throws IOException */
    public static void read() throws IOException{
    
        // 获取输入流
        FileInputStream fis = new FileInputStream("D:\\ideaProject\\helloWorld\\src\\main\\resources\\read.txt");
        // 获取通道
        FileChannel readChannel = fis.getChannel();
        // 创建一个1024字节大小的缓冲区
        ByteBuffer buf = ByteBuffer.allocate(1024);
        // 从通道读取数据到缓冲区，并返回读取的字节数
        int readBytes = readChannel.read(buf);
        // 读取的字节数不等于-1，说明有数据
        while(readBytes != -1){
    
            byte[] bs = new byte[readBytes];
            // 由写模式切换为读模式
            buf.flip();
            // 缓冲区还有数据可以读
            while(buf.hasRemaining()){
    
                buf.get(bs);
                String str = new String(bs, 0, readBytes);
                System.out.println(str);
            }
            // 清空缓冲区数据
            buf.clear();
            // 再次从通道中读取数据到缓冲区，知道没有数据
            readBytes = readChannel.read(buf);
        }
        fis.close();
    }


    /** * 写入文件 存在问题，待修改 * buffer -> channel -> 文件 * @throws IOException */
    public static void write() throws IOException {
    
        FileOutputStream fos = new FileOutputStream("D:\\ideaProject\\helloWorld\\src\\main\\resources\\write.txt");
        FileChannel channel = fos.getChannel();
        ByteBuffer buf = ByteBuffer.allocate(1024);
        buf.put("2312312312".getBytes(StandardCharsets.UTF_8));
        System.out.println(buf.toString());
        int writeBytes = channel.write(buf);
        fos.close();
    }


    /** * 文件复制 */
    public static void readThenWrite() throws IOException {
    
        FileInputStream fis = new FileInputStream("D:\\ideaProject\\helloWorld\\src\\main\\resources\\read.txt");
        FileOutputStream fos = new FileOutputStream("D:\\ideaProject\\helloWorld\\src\\main\\resources\\write.txt");
        FileChannel readChannel = fis.getChannel();
        FileChannel writeChannel = fos.getChannel();
        ByteBuffer buffer = ByteBuffer.allocate(1024);
        while(readChannel.read(buffer) != -1){
    
            // 切换为读模式
            buffer.flip();
            writeChannel.write(buffer);
            buffer.clear();
        }
        fis.close();
        fos.close();
    }

}