急！！！java导出csv文件，需要有代码展示

Question

本人已经生成了一个csv文件，到时如何把它导出，我写的测试时，response.getOutputStream()报空指针异常
finalOutFile = new File(fileName);
instream = new FileInputStream(finalOutFile);
outstream = response.getOutputStream();——这一行报空指针异常
response.setContentType("application/octet-stream");
response.setHeader("Content-disposition", "attachment; filename=" + java.net.URLEncoder.encode(finalOutFile.getName(), "UTF-8"));
response.setContentLength((int) finalOutFile.length());
System.out.println("===================" + finalOutFile.length());

Answer 1

response这个对象是不是为空