NIO的两种基本实现方式

1. 利用通道完成文件的复制(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");

            //获取通道
            inChannel = fis.getChannel();
            outChannel = fos.getChannel();

            //分配制定大小的缓冲区
            ByteBuffer buf = ByteBuffer.allocate(1024);

            //将通道中的数据存入缓冲区中
            while (inChannel.read(buf) != -1){
                //切换为读取数据的模式
                buf.flip();
                //将缓冲区中的数据写入通道
                outChannel.write(buf);
                buf.clear();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (outChannel != null){
                try {
                    outChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (inChannel != null){
                try {
                    inChannel.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fos != null){
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (fis != null){
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }

 

2. 使用直接缓冲区完成文件的复制(内存映射文件)

@Test
    public void test2() throws IOException{
        FileChannel inChannel = FileChannel.open(Paths.get("1.jpg"), StandardOpenOption.READ);
        FileChannel outChannel = FileChannel.open(Paths.get("3.jpg"), StandardOpenOption.READ,StandardOpenOption.WRITE,StandardOpenOption.CREATE_NEW);

        //内存映射文件
        MappedByteBuffer inMappedBuf = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());
        MappedByteBuffer outMappedBuf = 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[inMappedBuf.limit()];
        inMappedBuf.get(dst);
        outMappedBuf.put(dst);

        inChannel.close();
        outChannel.close();
    }

3. 通道之间的数据传输(底层自动创建缓冲区)

@Test
    public void test3() throws IOException{
        FileChannel inChannel = FileChannel.open(Paths.get("1.jpg"),StandardOpenOption.READ);
        FileChannel outChannel = FileChannel.open(Paths.get("4.jpg"),StandardOpenOption.READ,StandardOpenOption.WRITE,StandardOpenOption.CREATE_NEW);

        //inChannel.transferTo(0,inChannel.size(),outChannel);
        outChannel.transferFrom(inChannel,0,inChannel.size());

        inChannel.close();
        outChannel.close();
    }