1. 将File、FileInputStream 转换为byte数组
File file = new File("test.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);