在Web应用系统开发中，文件上传和下载功能是非常常用的功能，今天来讲一下JavaWeb中的文件上传和下载功能的实现。
1. 上传简单示例
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>文件上传下载</title></head><body><form action="${pageContext.request.contextPath}/UploadServlet" enctype="multipart/form-data" method="post"> 上传用户：<input type="text" name="username" /> <br /> 上传文件1：<input type="file" name="file1" /> <br /> 上传文件2：<input type="file" name="file2" /> <br /> <input type="submit" value="上传 "/></form> <br />${requestScope.message}</body></html>Servlet
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { try{ //1.得到解析器工厂 DiskFileItemFactory factory = new DiskFileItemFactory(); //2.得到解析器 ServletFileUpload upload = new ServletFileUpload(factory); //3.判断上传表单的类型 if(!upload.isMultipartContent(request)){ //上传表单为普通表单，则按照传统方式获取数据即可 return; } //为上传表单，则调用解析器解析上传数据 List<FileItem> list = upload.parseRequest(request); //FileItem //遍历list，得到用于封装第一个上传输入项数据fileItem对象 for(FileItem item : list){ if(item.isFormField()){ //得到的是普通输入项 String name = item.getFieldName(); //得到输入项的名称 String value = item.getString(); System.out.println(name + "=" + value); }else{ //得到上传输入项 String filename = item.getName(); //得到上传文件名 C:/Documents and Settings/ThinkPad/桌面/1.txt filename = filename.substring(filename.lastIndexOf("//")+1); InputStream in = item.getInputStream(); //得到上传数据 int len = 0; byte buffer[]= new byte[1024]; //用于保存上传文件的目录应该禁止外界直接访问 String savepath = this.getServletContext().getRealPath("/WEB-INF/upload"); System.out.println(savepath); FileOutputStream out = new FileOutputStream(savepath + "/" + filename); //向upload目录中写入文件 while((len=in.read(buffer))>0){ out.write(buffer, 0, len); } in.close(); out.close(); request.setAttribute("message", "上传成功"); } } }catch (Exception e) { request.setAttribute("message", "上传失败"); e.printStackTrace(); } }2. 修改后的上传功能：
注意事项：
1、上传文件名的中文乱码和上传数据的中文乱码
upload.setHeaderEncoding("UTF-8"); //解决上传文件名的中文乱码
//表单为文件上传，设置request编码无效,只能手工转换
1.1 value = new String(value.getBytes("iso8859-1"),"UTF-8");
1.2 String value = item.getString("UTF-8");
2.为保证服务器安全，上传文件应该放在外界无法直接访问的目录
3、为防止文件覆盖的现象发生，要为上传文件产生一个唯一的文件名
4、为防止一个目录下面出现太多文件，要使用hash算法打散存储
5.要限制上传文件的最大值，可以通过：ServletFileUpload.setFileSizeMax(1024)方法实现，并通过捕获：
FileUploadBase.FileSizeLimitExceededException异常以给用户友好提示
6.想确保临时文件被删除，一定要在处理完上传文件后，调用item.delete方法
7.要限止上传文件的类型：在收到上传文件名时，判断后缀名是否合法
8、监听文件上传进度：
ServletFileUpload upload = new ServletFileUpload(factory); upload.setProgressListener(new ProgressListener(){ public void update(long pBytesRead, long pContentLength, int arg2) { System.out.println("文件大小为：" + pContentLength + ",当前已处理：" + pBytesRead); } }); 9. 在web页面中动态添加文件上传输入项
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="删除"; del.onclick = function d(){ this.parentNode.parentNode.removeChild(this.parentNode); } var innerdiv = document.createElement("div"); innerdiv.appendChild(input); innerdiv.appendChild(del); div.appendChild(innerdiv); }上传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="删除"; 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>上传用户：</td> <td><input type="text" name="username"></td> </tr> <tr> <td>上传文件：</td> <td> <input type="button" value="添加上传文件" onclick="addinput()"> </td> </tr> <tr> <td></td> <td> <div id="file"> </div> </td> </tr> </table> </body></html>上传servlet
public class UploadServlet1 extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //request.getParameter("username"); //****错误 request.setCharacterEncoding("UTF-8"); //表单为文件上传，设置request编码无效 //得到上传文件的保存目录 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("文件大小为：" + pContentLength + ",当前已处理：" + pBytesRead); } });*/ upload.setHeaderEncoding("UTF-8"); //解决上传文件名的中文乱码 if(!upload.isMultipartContent(request)){ //按照传统方式获取数据 return; } /*upload.setFileSizeMax(1024); upload.setSizeMax(1024*10);*/ List<FileItem> list = upload.parseRequest(request); for(FileItem item : list){ if(item.isFormField()){ //fileitem中封装的是普通输入项的数据 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中封装的是上传文件 String filename = item.getName(); //不同的浏览器提交的文件是不一样 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); //得到文件保存的名称 String realSavePath = makePath(saveFilename, savePath); //得到文件的保存目录 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(); //删除临时文件 } } }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. 下载功能
//列出网站所有下载文件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_达.avi map.put(file.getName(), realname); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); }}jsp显示
<%@ 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}">下载</a> <br/> </c:forEach> </body></html>下载处理servlet
public class DownLoadServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String filename = request.getParameter("filename"); //23239283-92489-阿凡达.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", "您要下载的资源已被删除！！"); 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内容，希望对大家的学习有所帮助，也希望大家多多支持武林网。