9 File Upload and download

1. File Upload

      1. Modify the enctype of the form: <form action= "" method= "Post" enctype= "Multipart/form-data" > Modified servlet cannot pass REQ.GETP Arameter ("parameter name") accepts the request parameter 2. Import jar Package: Commons-fileupload-1.2.2.jar Commons-io-1.4.jar 3. Check method and Contenttyp        E boolean ismultipart=servletfileupload.ismultipartcontent (req);          if (!ismultipart) {return;      4. Create a factory object that handles Fileitem fileitemfactory factory=new diskfileitemfactory ();       Create a Processor object that handles file uploads Servletfileupload upload=new servletfileupload (Factory);       Parse Request Object List<fileitem> items=upload.parserequest (req);       for (Fileitem fileitem:items) {String fieldname=fileitem.getfiledname ();       if (Fileitem.isformfield ()) {String filename=fileitem.getstring ("Utf-8");           }else{String filename=fileitem.getname ();           String Contenttype=fileitem.getcontenttype ();           String Realpath=super.getservltcontext (). Getrealpath ("/upload"); FileiTem.write (New File (realpath+ "/" +filename));       }} 5. File name processing uses the UUID as the filename String uuid=uuid.randomuuid (). toString ();       String extension=filenameutils.getextension (fileName); Filename=uuid+ "."       Extension     6. Cache size and Temp directory settings cache size: Factory.setsizethreshold (500*1024); Set TEMP directory: Factory.setrepository (New File (""));

2. Uploading files using annotations

  @MultipartConfig     可以通过req.getParamter()接受参数 接受上传文件  Part part=req.getPart("");  part.write(realPath+"/"+name);

3. File download

  接受请求参数：      String fileName=req.getParameter("fileName");  fileName=new String(fileName.getBytes("ISO-8859-1"),"utf-8"); 找到资源的位置，读取到内存，响应给浏览器：      String realPath=super.getServletContext().getRealPath("");  String filePath=realPath+"\\"+fileName;  ServletOutputStream out=resp.getOutputStream();  //设置响应头   resp.setContenType("application/x-msdownload"); //获取请求头信息Use-Agent     String userAgent=req.getHeader("User-Agent"); if(userAgent.contain("MSIE")){    //IE    fileName=URLEncoder.encode(fileName,"utf-8"); }else{ //W3C    fileName=new String(fileName.getBytes("utf-8"),"ISO-8859-1"); } //设置下载的文件名称 resp.setHeader("Content-Disposition","attachment;fileName="+fileName); //将数据响应到浏览器 Files.copy(Paths.get(filePath),out);

9 file upload and download