在Web應用系統開發中，文件上傳和下載功能是非常常用的功能，今天來講一下JavaWeb中的文件上傳和下載功能的實現。
1. 上傳簡單示例
Jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>文件上傳下載</title></head><body><form action="${pageContext.request.contextPath}/UploadServlet" enctype="multipart/form-data" method="post"> 上傳用戶：<input type="text" name="username" /> <br /> 上傳文件1：<input type="file" name="file1" /> <br /> 上傳文件2：<input type="file" name="file2" /> <br /> <input type="submit" value="上傳"/></form> <br />${requestScope.message}</body></html>Servlet
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { try{ //1.得到解析器工廠DiskFileItemFactory factory = new DiskFileItemFactory(); //2.得到解析器ServletFileUpload upload = new ServletFileUpload(factory); //3.判斷上傳表單的類型if(!upload.isMultipartContent(request)){ //上傳表單為普通表單，則按照傳統方式獲取數據即可return; } //為上傳表單，則調用解析器解析上傳數據List<FileItem> list = upload.parseRequest(request); //FileItem //遍歷list，得到用於封裝第一個上傳輸入項數據fileItem對象for(FileItem item : list){ if(item.isFormField()){ //得到的是普通輸入項String name = item.getFieldName(); //得到輸入項的名稱String value = item.getString(); System.out.println(name + "=" + value); }else{ //得到上傳輸入項String filename = item.getName(); //得到上傳文件名C:/Documents and Settings/ThinkPad/桌面/1.txt filename = filename.substring(filename.lastIndexOf("//")+1); InputStream in = item.getInputStream(); //得到上傳數據int len = 0; byte buffer[]= new byte[1024]; //用於保存上傳文件的目錄應該禁止外界直接訪問String savepath = this.getServletContext().getRealPath("/WEB-INF/upload"); System.out.println(savepath); FileOutputStream out = new FileOutputStream(savepath + "/" + filename); //向upload目錄中寫入文件while((len=in.read(buffer))>0){ out.write(buffer, 0, len); } in.close(); out.close(); request.setAttribute("message", "上傳成功"); } } }catch (Exception e) { request.setAttribute("message", "上傳失敗"); e.printStackTrace(); } }2. 修改後的上傳功能：
注意事項：
1、上傳文件名的中文亂碼和上傳數據的中文亂碼
upload.setHeaderEncoding("UTF-8"); //解決上傳文件名的中文亂碼
//表單為文件上傳，設置request編碼無效,只能手工轉換
1.1 value = new String(value.getBytes("iso8859-1"),"UTF-8");
1.2 String value = item.getString("UTF-8");
2.為保證服務器安全，上傳文件應該放在外界無法直接訪問的目錄
3、為防止文件覆蓋的現象發生，要為上傳文件產生一個唯一的文件名
4、為防止一個目錄下面出現太多文件，要使用hash算法打散存儲
5.要限制上傳文件的最大值，可以通過：ServletFileUpload.setFileSizeMax(1024)方法實現，並通過捕獲：
FileUploadBase.FileSizeLimitExceededException異常以給用戶友好提示
6.想確保臨時文件被刪除，一定要在處理完上傳文件後，調用item.delete方法
7.要限止上傳文件的類型：在收到上傳文件名時，判斷後綴名是否合法
8、監聽文件上傳進度：
ServletFileUpload upload = new ServletFileUpload(factory); upload.setProgressListener(new ProgressListener(){ public void update(long pBytesRead, long pContentLength, int arg2) { System.out.println("文件大小為：" + pContentLength + ",當前已處理：" + pBytesRead); } }); 9. 在web頁面中動態添加文件上傳輸入項
function addinput(){ var div = document.getElementById("file"); var input = document.createElement("input"); input.type="file"; input.name="filename"; var del = document.createElement("input"); del.type="button"; del.value="刪除"; del.onclick = function d(){ this.parentNode.parentNode.removeChild(this.parentNode); } var innerdiv = document.createElement("div"); innerdiv.appendChild(input); innerdiv.appendChild(del); div.appendChild(innerdiv); }上傳jsp:
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>My JSP 'upload2.jsp' starting page</title> <script type="text/javascript"> function addinput(){ var div = document.getElementById("file"); var input = document.createElement("input"); input.type="file"; input.name="filename"; var del = document.createElement("input"); del.type="button"; del.value="刪除"; del.onclick = function d(){ this.parentNode.parentNode.removeChild(this.parentNode); } var innerdiv = document.createElement("div"); innerdiv.appendChild(input); innerdiv.appendChild(del); div.appendChild(innerdiv); } </script> </head> <body> <form action="" enctype="mutlipart/form-data"></form> <table> <tr> <td>上傳用戶：</td> <td><input type="text" name="username"></td> </tr> <tr> <td>上傳文件：</td> <td> <input type="button" value="添加上傳文件" onclick="addinput()"> </td> </tr> <tr> <td></td> <td> <div id="file"> </div> </td> </tr> </table> </body></html>上傳servlet
public class UploadServlet1 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //request.getParameter("username"); //****錯誤request.setCharacterEncoding("UTF-8"); //表單為文件上傳，設置request編碼無效//得到上傳文件的保存目錄String savePath = this.getServletContext().getRealPath("/WEB-INF/upload"); try{ DiskFileItemFactory factory = new DiskFileItemFactory(); factory.setRepository(new File(this.getServletContext().getRealPath("/WEB-INF/temp"))); ServletFileUpload upload = new ServletFileUpload(factory); /*upload.setProgressListener(new ProgressListener(){ public void update(long pBytesRead, long pContentLength, int arg2) { System.out.println("文件大小為：" + pContentLength + ",當前已處理：" + pBytesRead); } });*/ upload.setHeaderEncoding("UTF-8"); //解決上傳文件名的中文亂碼if(!upload.isMultipartContent(request)){ //按照傳統方式獲取數據return; } /*upload.setFileSizeMax(1024); upload.setSizeMax(1024*10);*/ List<FileItem> list = upload.parseRequest(request); for(FileItem item : list){ if(item.isFormField()){ //fileitem中封裝的是普通輸入項的數據String name = item.getFieldName(); String value = item.getString("UTF-8"); //value = new String(value.getBytes("iso8859-1"),"UTF-8"); System.out.println(name + "=" + value); }else{ //fileitem中封裝的是上傳文件String filename = item.getName(); //不同的瀏覽器提交的文件是不一樣c:/a/b/1.txt 1.txt System.out.println(filename); if(filename==null || filename.trim().equals("")){ continue; } filename = filename.substring(filename.lastIndexOf("//")+1); InputStream in = item.getInputStream(); String saveFilename = makeFileName(filename); //得到文件保存的名稱String realSavePath = makePath(saveFilename, savePath); //得到文件的保存目錄FileOutputStream out = new FileOutputStream(realSavePath + "//" + saveFilename); byte buffer[] = new byte[1024]; int len = 0; while((len=in.read(buffer))>0){ out.write(buffer, 0, len); } in.close(); out.close(); item.delete(); //刪除臨時文件} } }catch (FileUploadBase.FileSizeLimitExceededException e) { e.printStackTrace(); request.setAttribute("message", "文件超出最大值！ ！ ！ "); request.getRequestDispatcher("/message.jsp").forward(request, response); return; } catch (Exception e) { e.printStackTrace(); } } public String makeFileName(String filename){ //2.jpg return UUID.randomUUID().toString() + "_" + filename; } public String makePath(String filename,String savePath){ int hashcode = filename.hashCode(); int dir1 = hashcode&0xf; //0--15 int dir2 = (hashcode&0xf0)>>4; //0-15 String dir = savePath + "//" + dir1 + "//" + dir2; //upload/2/3 upload/3/5 File file = new File(dir); if(!file.exists()){ file.mkdirs(); } return dir; } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}3. 下載功能
//列出網站所有下載文件public class ListFileServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String filepath = this.getServletContext().getRealPath("/WEB-INF/upload"); Map map = new HashMap(); listfile(new File(filepath),map); request.setAttribute("map", map); request.getRequestDispatcher("/listfile.jsp").forward(request, response); } public void listfile(File file,Map map){ if(!file.isFile()){ File files[] = file.listFiles(); for(File f : files){ listfile(f,map); } }else{ String realname = file.getName().substring(file.getName().indexOf("_")+1); //9349249849-88343-8344_阿_凡_達.avi map.put(file.getName(), realname); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}jsp顯示
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head> <title>My JSP 'listfile.jsp' starting page</title> </head> <body> <c:forEach var="me" items="${map}"> <c:url value="/servlet/DownLoadServlet" var="downurl"> <c:param name="filename" value="${me.key}"></c:param> </c:url> ${me.value } <a href="${downurl}">下載</a> <br/> </c:forEach> </body></html>下載處理servlet
public class DownLoadServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String filename = request.getParameter("filename"); //23239283-92489-阿凡達.avi filename = new String(filename.getBytes("iso8859-1"),"UTF-8"); String path = makePath(filename,this.getServletContext().getRealPath("/WEB-INF/upload")); File file = new File(path + "//" + filename); if(!file.exists()){ request.setAttribute("message", "您要下載的資源已被刪除！！"); request.getRequestDispatcher("/message.jsp").forward(request, response); return; } String realname = filename.substring(filename.indexOf("_")+1); response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(realname, "UTF-8")); FileInputStream in = new FileInputStream(path + "//" + filename); OutputStream out = response.getOutputStream(); byte buffer[] = new byte[1024]; int len = 0; while((len=in.read(buffer))>0){ out.write(buffer, 0, len); } in.close(); out.close(); } public String makePath(String filename,String savePath){ int hashcode = filename.hashCode(); int dir1 = hashcode&0xf; //0--15 int dir2 = (hashcode&0xf0)>>4; //0-15 String dir = savePath + "//" + dir1 + "//" + dir2; //upload/2/3 upload/3/5 File file = new File(dir); if(!file.exists()){ file.mkdirs(); } return dir; } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。