【小家Spring】Spring MVC容器的web九大组件之---HandlerAdapter源码详解---HttpMessageConverter的匹配规则（选择原理）(下)

    //设置响应头和客户端保存文件名
    response.setCharacterEncoding("utf-8");
    response.setContentType("multipart/form-data");
    response.setHeader("Content-Disposition", "attachment;fileName=" + fileName);
  ...
        //打开本地文件流
        InputStream inputStream = new FileInputStream(filePath);
        //激活下载操作
        OutputStream os = response.getOutputStream();
        //循环写入输出流
        byte[] b = new byte[2048];
        int length;
        while ((length = inputStream.read(b)) > 0) {
            os.write(b, 0, length);
            downloadedLength += b.length;
        }
        // 这里主要关闭。
        os.close();
        inputStream.close();
  ...

    // 处理下载 get/post/put请求等等都是可以的  但一般都用get请求
    @RequestMapping(value = "/download", method = RequestMethod.GET)
    public ResponseEntity<Resource> downloadFile(@RequestParam String fileName) {
        // 构造下载对象  读取出一个Resource出来  此处以类路径下的logback.xml
        DownloadFileInfoDto downloadFile = new DownloadFileInfoDto(fileName, new ClassPathResource("logback.xml"));
        return downloadResponse(downloadFile);
    }
    @Getter
    @Setter
    @NoArgsConstructor
    @AllArgsConstructor
    private static class DownloadFileInfoDto {
        private String fileName; // 下载的文件
        private Resource resource; // 下载的具体文件资源
    }
    // 共用方法  兼容到了IE浏览器~~~
    private static ResponseEntity<Resource> downloadResponse(
            DownloadFileInfoDto fileInfo) {
        String fileName = fileInfo.getFileName();
        Resource body = fileInfo.getResource();
        // ========通过User-Agent来判断浏览器类型 做一定的兼容~========
        HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();
        String header = request.getHeader("User-Agent").toUpperCase();
        HttpStatus status = HttpStatus.CREATED;
        try {
            if (header.contains("MSIE") || header.contains("TRIDENT") || header.contains("EDGE")) {
                fileName = URLEncoder.encode(fileName, "UTF-8");
                fileName = fileName.replace("+", "%20");    // IE下载文件名空格变+号问题
                status = HttpStatus.OK;
            } else { // 其它浏览器 比如谷歌浏览器等等~~~~
                fileName = new String(fileName.getBytes("UTF-8"), "ISO8859-1");
            }
        } catch (UnsupportedEncodingException e) {
        }
        // =====响应头需设置为MediaType.APPLICATION_OCTET_STREAM=====
        HttpHeaders headers = new HttpHeaders();
    // 注意：若这个响应头不是必须的，但是如果你确定要下载，建议写上这个响应头~
        headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        // 此处，如果你自己没有设置这个请求头，浏览器肯定就不会弹窗对话框了。它就会以body的形式直接显示在浏览器上
        headers.setContentDispositionFormData("attachment", fileName);
        return new ResponseEntity<>(body, headers, status);
    }

Content-Type: application/octet-stream
Content-Disposition: attachment; filename="picture.png"

@RequestMapping("/testResponseEntity")
public ResponseEntity<byte[]> testResponseEntity(HttpSession session) throws IOException {
    byte[] body = null;
    ServletContext servletContext = session.getServletContext();
    InputStream in = servletContext.getResourceAsStream("/files/abc.txt");
    body = new byte[in.available()];
    in.read(body);
    HttpHeaders headers = new HttpHeaders();
    headers.add("Content-Disposition","attachment;filename=abc.txt");
    HttpStatus statusCode = HttpStatus.OK;
    ResponseEntity<byte[]> response = new ResponseEntity<byte[]>(body,headers,statusCode);
    return  response;
}

        // =====响应头需设置为MediaType.APPLICATION_OCTET_STREAM=====
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        //headers.setContentDispositionFormData("attachment", fileName);

        // =====响应头需设置为MediaType.APPLICATION_OCTET_STREAM=====
        HttpHeaders headers = new HttpHeaders();
        //headers.setContentType(MediaType.APPLICATION_OCTET_STREAM);
        //headers.setContentDispositionFormData("attachment", fileName);

  private void addContentDispositionHeader(ServletServerHttpRequest request, ServletServerHttpResponse response) {
    ...
    // 默认它采用inline的模式
    if (!safeExtension(servletRequest, ext) || !safeExtension(servletRequest, extInPathParams)) {
      headers.add(HttpHeaders.CONTENT_DISPOSITION, "inline;filename=f.txt");
    }
    ...
  }

public abstract class AbstractMessageConverterMethodProcessor extends AbstractMessageConverterMethodArgumentResolver implements HandlerMethodReturnValueHandler {
  /* Extensions associated with the built-in message converters */
  private static final Set<String> WHITELISTED_EXTENSIONS = new HashSet<>(Arrays.asList(
      "txt", "text", "yml", "properties", "csv",
      "json", "xml", "atom", "rss",
      "png", "jpe", "jpeg", "jpg", "gif", "wbmp", "bmp"));
  private static final Set<String> WHITELISTED_MEDIA_BASE_TYPES = new HashSet<>(
      Arrays.asList("audio", "image", "video"));
  ...
}