1、将File、FileInputStream 转换为byte数组：

    File file = new File("file.txt");

    InputStream input = new FileInputStream(file);

    byte[] byt = new byte[input.available()];

    input.read(byt);

2、将byte数组转换为InputStream：

    byte[] byt = new byte[1024];

    InputStream input = new ByteArrayInputStream(byt);

3、将byte数组转换为File：

    File file = new File('');

    OutputStream output = new FileOutputStream(file);

    BufferedOutputStream bufferedOutput = new BufferedOutputStream(output);

    bufferedOutput.write(byt);