转换流（字节流转换成字符流）

InputStreamReader ：将输入字节流转换成输入字符流

OutputStreamWriter： 将输出字节流转换成输出字符流

InputStreamReader inputStreamReader = new InputStreamReader(new FileInputStream(new File("C:/a.txt")));

OutputStreamWriter outputStreamWriter = new OutputStreamWriter(new FileOutputStream(new File("C:/a.txt")));