工程目錄結構：
檔案上傳：
檔案上傳用到了commons-fileupload-1.2.1.jar和commons-io-1.4.jar兩個jar包。指定將檔案上傳到伺服器的store目錄下。
fileupload.jsp:
<%@ page contentType="text/html;charset=UTF-8" pageEncoding="UTF-8"%><html><head><title>Insert title here</title></head><body><form action="upload" method="post" enctype="multipart/form-data">姓名:<input type="text" name="username" size="14"><br>檔案:<input type="file" name="file1" size="14"><input type="submit" value="上傳"></form></body></html>
這裡需要注意兩點：第一method方法必須修改為post。第二為form標籤添加enctype屬性，且值必須為multipart/form-data。<form>標記的enctype屬性的預設值為"application/x-www-form-urlencoded"，也就是說若未明確添加enctype屬性，則使用這個預設值。enctype屬性用於指定表單資料的MIME類型，預設值表示表單資料會採用“名字=值”的形式。而對於檔案上傳，這裡必須取值“multipart/form-data”。
FileUploadServlet.java：
public class FileUploadServlet extends HttpServlet {public void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("UTF-8");DiskFileItemFactory factory=new DiskFileItemFactory();ServletFileUpload sfu=new ServletFileUpload(factory);try {List<FileItem> items=sfu.parseRequest(request);for(int i=0;i<items.size();i++){FileItem item=items.get(i);if(item.isFormField()){//普通表單域String paraName=item.getFieldName();String paraValue=item.getString();}else{//檔案域ServletContext ctx=getServletContext();String path=ctx.getRealPath("store");String fileName=item.getName();fileName=fileName.substring(fileName.lastIndexOf("/")+1);File file=new File(path+"/"+fileName);item.write(file);}}} catch (FileUploadException e) {e.printStackTrace();} catch (Exception e) {e.printStackTrace();}}}
點擊上傳，然後到伺服器的應用下的store目錄下可看到剛才上傳的檔案。
檔案下載：
filedownload.jsp:
<%@ page contentType="text/html;charset=UTF-8" pageEncoding="UTF-8"%><html><head><title>Insert title here</title></head><body><form action="download">輸入要下載的檔案名稱:<br><input type="text" name="filename"><input type="submit" value="開始下載"></form></body></html>
我們輸入剛才上傳的web.jpg檔案：
FileDownloadServlet.java:
public class FileDownloadServlet extends HttpServlet {public void service(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("UTF-8");String filename=request.getParameter("filename");System.out.println(filename);response.setContentType("application/force-download");response.setHeader("Content-Disposition","attachment;filename="+filename);ServletContext ctx=getServletContext();InputStream in=ctx.getResourceAsStream("store/"+filename);System.out.println(in==null);OutputStream out=response.getOutputStream();int hasRead=0;byte[] buffer=new byte[1024];while((hasRead=in.read(buffer))!=-1){out.write(buffer,0,hasRead);}out.close();in.close();}}
點擊開始下載，可以看到瀏覽器彈出提示下載框。
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