JavaWeb文件上传下载功能示例解析
发布于 2017-11-19 11:24:20 | 171 次阅读 | 评论: 0 | 来源: 网友投递
Java程序设计语言
java 是一种可以撰写跨平台应用软件的面向对象的程序设计语言，是由Sun Microsystems公司于1995年5月推出的Java程序设计语言和Java平台（即JavaEE(j2ee), JavaME(j2me), JavaSE(j2se)）的总称。
这篇文章主要介绍了JavaWeb中的文件上传和下载功能的实现，文件上传和下载功能是非常常用的功能,需要的朋友可以参考下
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PHPERZ。
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