@RequestMapping(value = "down1", method = RequestMethod.GET)
public void downloadAllClassmate(HttpServletResponse response) throws IOException {    byte[] bytes = new byte[100];
    String fileName="test.pdf";
    response.setContentType("application/pdf"); // 设置文件格式
    response.setHeader("Content-disposition", "attachment;filename=" + fileName);// 设置文件名
    response.setHeader("Content-Length", "102400");// 设置文件大小
    response.flushBuffer();
    response.getOutputStream().write(bytes); // 写文件到响应体重
}

@RequestMapping(value = "/down2")
    public ResponseEntity<byte[]> pdfDownload(HttpServletRequest httpServletRequest, HttpServletResponse response) throws IOException {
        String path = "d:/c.pdf";
        File file = new File(path);
        HttpHeaders httpHeaders = new HttpHeaders();
        String fileName = file.getName();
//         设置文件名
        httpHeaders.setContentDispositionFormData("attachment", java.net.URLEncoder.encode(fileName, "UTF-8"));
//         设置响应格式
        httpHeaders.setContentType(MediaType.parseMediaType("application/pdf"));
//         将 file 放在 ResponseEntity 中返回
        return new ResponseEntity<byte[]>(FileUtils.readFileToByteArray(file),
                httpHeaders,
                HttpStatus.CREATED);
    }

不同的 ContentType 会影响客户端所看到的效果. 默认的 ContentType 为 text/html

也就是网页格式.
代码如:

显示的为网页, 而

则会显示 html 原代码.

以下为一些常用的 ContentType

下面是更详细的 ContentType
'ez' => 'application/andrew-inset', 
'hqx' => 'application/mac-binhex40', 
'cpt' => 'application/mac-compactpro', 
'doc' => 'application/msword', 
'bin' => 'application/octet-stream', 
'dms' => 'application/octet-stream', 
'lha' => 'application/octet-stream', 
'lzh' => 'application/octet-stream', 
'exe' => 'application/octet-stream', 
'class' => 'application/octet-stream', 
'so' => 'application/octet-stream', 
'dll' => 'application/octet-stream', 
'oda' => 'application/oda', 
'pdf' => 'application/pdf', 
'ai' => 'application/postscript', 
'eps' => 'application/postscript', 
'ps' => 'application/postscript', 
'smi' => 'application/smil', 
'smil' => 'application/smil', 
'mif' => 'application/vnd.mif', 
'xls' => 'application/vnd.ms-excel', 
'ppt' => 'application/vnd.ms-powerpoint', 
'wbxml' => 'application/vnd.wap.wbxml', 
'wmlc' => 'application/vnd.wap.wmlc', 
'wmlsc' => 'application/vnd.wap.wmlscriptc', 
'bcpio' => 'application/x-bcpio', 
'vcd' => 'application/x-cdlink', 
'pgn' => 'application/x-chess-pgn', 
'cpio' => 'application/x-cpio', 
'csh' => 'application/x-csh', 
'dcr' => 'application/x-director', 
'dir' => 'application/x-director', 
'dxr' => 'application/x-director', 
'dvi' => 'application/x-dvi', 
'spl' => 'application/x-futuresplash', 
'gtar' => 'application/x-gtar', 
'hdf' => 'application/x-hdf', 
'js' => 'application/x-javascript', 
'skp' => 'application/x-koan', 
'skd' => 'application/x-koan', 
'skt' => 'application/x-koan', 
'skm' => 'application/x-koan', 
'latex' => 'application/x-latex', 
'nc' => 'application/x-netcdf', 
'cdf' => 'application/x-netcdf', 
'sh' => 'application/x-sh', 
'shar' => 'application/x-shar', 
'swf' => 'application/x-shockwave-flash', 
'sit' => 'application/x-stuffit', 
'sv4cpio' => 'application/x-sv4cpio', 
'sv4crc' => 'application/x-sv4crc', 
'tar' => 'application/x-tar', 
'tcl' => 'application/x-tcl', 
'tex' => 'application/x-tex', 
'texinfo' => 'application/x-texinfo', 
'texi' => 'application/x-texinfo', 
't' => 'application/x-troff', 
'tr' => 'application/x-troff', 
'roff' => 'application/x-troff', 
'man' => 'application/x-troff-man', 
'me' => 'application/x-troff-me', 
'ms' => 'application/x-troff-ms', 
'ustar' => 'application/x-ustar', 
'src' => 'application/x-wais-source', 
'xhtml' => 'application/xhtml+xml', 
'xht' => 'application/xhtml+xml', 
'zip' => 'application/zip', 
'au' => 'audio/basic', 
'snd' => 'audio/basic', 
'mid' => 'audio/midi', 
'midi' => 'audio/midi', 
'kar' => 'audio/midi', 
'mpga' => 'audio/mpeg', 
'mp2' => 'audio/mpeg', 
'mp3' => 'audio/mpeg', 
'aif' => 'audio/x-aiff', 
'aiff' => 'audio/x-aiff', 
'aifc' => 'audio/x-aiff', 
'm3u' => 'audio/x-mpegurl', 
'ram' => 'audio/x-pn-realaudio', 
'rm' => 'audio/x-pn-realaudio', 
'rpm' => 'audio/x-pn-realaudio-plugin', 
'ra' => 'audio/x-realaudio', 
'wav' => 'audio/x-wav', 
'pdb' => 'chemical/x-pdb', 
'xyz' => 'chemical/x-xyz', 
'bmp' => 'image/bmp', 
'gif' => 'image/gif', 
'ief' => 'image/ief', 
'jpeg' => 'image/jpeg', 
'jpg' => 'image/jpeg', 
'jpe' => 'image/jpeg', 
'png' => 'image/png', 
'tiff' => 'image/tiff', 
'tif' => 'image/tiff', 
'djvu' => 'image/vnd.djvu', 
'djv' => 'image/vnd.djvu', 
'wbmp' => 'image/vnd.wap.wbmp', 
'ras' => 'image/x-cmu-raster', 
'pnm' => 'image/x-portable-anymap', 
'pbm' => 'image/x-portable-bitmap', 
'pgm' => 'image/x-portable-graymap', 
'ppm' => 'image/x-portable-pixmap', 
'rgb' => 'image/x-rgb', 
'xbm' => 'image/x-xbitmap', 
'xpm' => 'image/x-xpixmap', 
'xwd' => 'image/x-xwindowdump', 
'igs' => 'model/iges', 
'iges' => 'model/iges', 
'msh' => 'model/mesh', 
'mesh' => 'model/mesh', 
'silo' => 'model/mesh', 
'wrl' => 'model/vrml', 
'vrml' => 'model/vrml', 
'css' => 'text/css', 
'html' => 'text/html', 
'htm' => 'text/html', 
'asc' => 'text/plain', 
'txt' => 'text/plain', 
'rtx' => 'text/richtext', 
'rtf' => 'text/rtf', 
'sgml' => 'text/sgml', 
'sgm' => 'text/sgml', 
'tsv' => 'text/tab-separated-values', 
'wml' => 'text/vnd.wap.wml', 
'wmls' => 'text/vnd.wap.wmlscript', 
'etx' => 'text/x-setext', 
'xsl' => 'text/xml', 
'xml' => 'text/xml', 
'mpeg' => 'video/mpeg', 
'mpg' => 'video/mpeg', 
'mpe' => 'video/mpeg', 
'qt' => 'video/quicktime', 
'mov' => 'video/quicktime', 
'mxu' => 'video/vnd.mpegurl', 
'avi' => 'video/x-msvideo', 
'movie' => 'video/x-sgi-movie', 
'ice' => 'x-conference/x-cooltalk'