本文介绍如何使用JSP和Servlet实现文件的上传和下载功能。详细解释了使用multipart/form-data编码方式上传文件的原理，以及如何在Servlet中处理上传的文件。同时，文章还展示了如何设置HTTP响应头实现文件下载。
第一种方法JSP+Servlet
一、文件上传下载原理
在TCP/IP中，最早出现的文件上传机制是FTP。它是将文件由客户端发送到服务器的标准机制。但是在jsp编程中不能使用FTP方法来上传文件，这是由jsp的运行机制所决定的。
通过为表单元素设置Method=“post” enctype=”multipart/form-data”属性，让表单提交的数据以二进制编码的方式提交，在接收此请求的Servlet中用二进制流来获取内容，就可以取得上传文件的内容，从而实现文件的上传。
二、enctype属性的选择值范围
1、application/x-www-form-urlencoded:这是默认编码方式，它只处理表单域里的value属性值，采用这种编码方式的表单会将表单域的值处理成url编码方式。
2、multipart/form-data:这种编码方式的表单会以二进制流的方式来处理表单数据，这种编码方式会把文件域指定的文件内容也封装到请求参数里。
3、text/plain:这种方式主要适用于直接通过表单发送邮件的方式。
三、代码内容
1.将文件读取到服务器指定目录下
2.获取文件内容的起止位置，和文件名称
3.将文件保存到项目的指定目录下
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//从request中获取输入流信息
InputStream fileSource = request.getInputStream();
//创建存储在服务器的路径信息
String tempFileName = "H:/tempFile";
//指向临时文件
File tempFile = new File(tempFileName);
//outPutStream输出流指向临时文件
FileOutputStream outputStream = new FileOutputStream(tempFile);
//每次读取文件字节
byte b[] = new byte[1024];
int n;
while((n=fileSource.read(b))!=-1){
outputStream.write(b,0,n);
}
//关闭输出输入流
fileSource.close();
outputStream.close();
//获取上传文件的名称
RandomAccessFile randomFile = new RandomAccessFile(tempFile, "r");
randomFile.readLine(); //获取第一行数据（对我们来说没有意义）
String str = randomFile.readLine(); //获取第二行数据，内容为：Content-Disposition: form-data; name="myfile"; filename="C:\Users\lihf\Desktop\hello.txt"
int beginIndex = str.lastIndexOf("\\")+1;
int endIndex = str.lastIndexOf("\"");
String fileName = str.substring(beginIndex, endIndex);
//重新定位文件指针到头文件
randomFile.seek(0);
long startPosition=0;
int i=1;
//获取文件内容开始位置
while((n=randomFile.readByte())!=-1&&i<=4){
if(n=='\n'){
startPosition = randomFile.getFilePointer();
i++;
}
}
startPosition = randomFile.getFilePointer() -1;
//获取文件结束位置
randomFile.seek(randomFile.length()); //文件指针定位到文件末尾
long endPosition = randomFile.getFilePointer();
int j=1;
while(endPosition>=0&&j<=2){
endPosition--;
randomFile.seek(endPosition);
if(randomFile.readByte()=='\n'){
j++;
}
}
endPosition = endPosition -1;
//设置保存文件上传的路径
String realPath = getServletContext().getRealPath("/")+"images";
System.out.println("保存文件上传的路径："+realPath);
File fileupload = new File(realPath);
if(!fileupload.exists()){
fileupload.mkdir(); //创建此抽象路径名指定的目录。
}
File saveFile = new File(realPath, fileName);
RandomAccessFile randomAccessFile = new RandomAccessFile(saveFile,"rw");
//从临时文件中读取文件内容（根据文件起止位置获取）
randomFile.seek(startPosition);
while(startPosition<endPosition){
randomAccessFile.write(randomFile.readByte());
startPosition = randomFile.getFilePointer();
}
//关闭输入输出流
randomAccessFile.close();
randomFile.close();
tempFile.delete();
request.setAttribute("result", "上传成功！");
RequestDispatcher dispatcher = request.getRequestDispatcher("jsp/01.jsp");
dispatcher.forward(request, response);
}
三、文件下载原理
1、step1:需要通过HttpServletResponse.setContentType方法设置Content-type头字段的值，为浏览器无法使用某种方式或激活某个程序来处理的MIME类型，例如，“application/octet-stream”或“application/x-msdownload”等。
2、step2:需要通过HttpServletResponse.setHeader方法设置Content-Disposition头的值为“attachment；filename=文件名”。
3、step3:读取下载文件，调用HttpServletResponse.getOutputStream方法返回的OutputStream对象来向客户端写入附件文件内容。
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//获取文件下载路径
String path = getServletContext().getRealPath("/") + "images/";
String filename = request.getParameter("filename");
File file = new File(path + filename);
if(file.exists()){
//设置相应类型application/octet-stream
response.setContentType("application/x-msdownload");
//设置头信息
response.setHeader("Content-Disposition", "attachment;filename=\"" + filename + "\"");
InputStream inputStream = new FileInputStream(file);
ServletOutputStream ouputStream = response.getOutputStream();
byte b[] = new byte[1024];
int n ;
while((n = inputStream.read(b)) != -1){
ouputStream.write(b,0,n);
}
//关闭流、释放资源
ouputStream.close();
inputStream.close();
}else{
request.setAttribute("errorResult", "文件不存在下载失败！");
RequestDispatcher dispatcher = request.getRequestDispatcher("jsp/01.jsp");
dispatcher.forward(request, response);
}
}SP页面内容：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP '01.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<link rel="stylesheet" type="text/css" href="css/common.css" />
<script type="text/javascript" src="js/jquery-1.11.1.js"></script>
<script type="text/javascript">
$(function(){
$(".thumbs a").click(function(){
var largePath=$(this).attr("href");
var largeAlt=$(this).attr("title");
$("#largeImg").attr({
src:largePath,
alt:largeAlt
});
return false;
});
$("#myfile").change(function(){
$("previewImg").attr("src","file:///"+$("#myfile").val());
});
var la = $("#large");
la.hide();
$("#previewImg").mousemove(function(e){
la.css({
top:e.pagey,
left:e.pagex
}).html('<img src="'+this.src+'" />');
}).mouseout(function(){
la.hide();
});
});
/* function showPreview(obj){
var str = obj.value;
document.getElementById("previewImg").innerHTML=
"<img src='"+str+"'/>";
alert(document.getElementById("previewImg").innerHTML);
} */
</script>
</head>
<body>
<img id="previewImg" src="images/preview.jpg" width="80" height="80" />
<form action="uploadServlet.do" method="post" enctype="multipart/form-data">
请选择上传图片：<input type="file" id="myfile" name="myfile" onchange="showPreview(this)" />
<input type="submit" value="提交"/>
</form>
下载<a href="downloadServlet.do?filename=hello.txt">hello.txt</a> ${errorResult}
<div id="large"></div>
<!-- <form action="">
请选择上传图片：<input type="file" id="myfile" name="myfile" onchange="showPreview(this)" />
<div id="previewImg"></div>
</form> -->
<hr>
<h2>图片预览</h2>
<p><img id="largeImg" src="images/img1-lg.jpg" alt="Large Image"/></p>
<p class="thumbs">
<a href="images/img2-lg.jpg" title="Image2"><img src="images/img2-thumb.jpg"></a>
<a href="images/img3-lg.jpg" title="Image3"><img src="images/img3-thumb.jpg"></a>
<a href="images/img4-lg.jpg" title="Image4"><img src="images/img4-thumb.jpg"></a>
<a href="images/img5-lg.jpg" title="Image5"><img src="images/img5-thumb.jpg"></a>
<a href="images/img6-lg.jpg" title="Image6"><img src="images/img6-thumb.jpg"></a>
</p>
</body>
</html>第二种方法SmartUpload实现上传下载
使用非常简单，直接引入SmartUpload的jar文件就可以啦
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置上传文件保存路径
String filePath = getServletContext().getRealPath("/")+"images";
File file = new File(filePath);
if(!file.exists()){
file.mkdir();
}
SmartUpload su = new SmartUpload();
//初始化smartUpload
su.initialize(getServletConfig(), request, response);
//设置上传文件大小
su.setMaxFileSize(1024*1024*10);
//设置所有文件的大小
su.setTotalMaxFileSize(102481024*100);
//设置允许上传文件的类型
su.setAllowedFilesList("txt,jpg,gif");
String result = "上传能成功";
try {
//设置禁止上传文件类型
su.setDeniedFilesList("jsp,rar");
su.upload();
int count = su.save(filePath);
System.out.println("上传成功"+count+"文件！");
} catch (Exception e) {
result="上传文件失败！";
<span style="white-space:pre"> </span>if(e.getMessage().indexOf("1015")!=-1){<span style="white-space:pre"> </span>
<span style="white-space:pre"> </span>result = "上传文件失败:上传文件类型不正确！";
<span style="white-space:pre"> </span>}else if(e.getMessage().indexOf("1010")!=-1){
<span style="white-space:pre"> </span>result = "上传文件失败:上传文件类型不正确！";
<span style="white-space:pre"> </span>}else if(e.getMessage().indexOf("1105")!=-1){
<span style="white-space:pre"> </span>result = "上传文件失败:上传文件大小大于允许上传的最大值！";
<span style="white-space:pre"> </span>}else if(e.getMessage().indexOf("1110")!=-1){
<span style="white-space:pre"> </span>result = "上传文件失败:上传文件的总大小大于我们允许上传总大小的最大值！";
<span style="white-space:pre"> </span>}
<span style="white-space:pre"> </span>e.printStackTrace();
}
for(int i=0;i<su.getFiles().getCount();i++){
<span style="white-space:pre"> </span>com.jspsmart.upload.File tempFile = su.getFiles().getFile(i);
<span style="white-space:pre"> </span>System.out.println("表单当中name属性值："+tempFile.getFieldName());
<span style="white-space:pre"> </span>System.out.println("上传文件名："+tempFile.getFileName());
<span style="white-space:pre"> </span>System.out.println("上传文件的大小："+tempFile.getSize());
<span style="white-space:pre"> </span>System.out.println("上传文件名拓展名："+tempFile.getFileExt());
<span style="white-space:pre"> </span>System.out.println("上传文件的全名："+tempFile.getFilePathName());
<span style="white-space:pre"> </span>}
request.setAttribute("result",result);
request.getRequestDispatcher("jsp/02.jsp").forward(request, response);
}jsp页面表单提交内容：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP '02.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<link rel="stylesheet" type="text/css" href="css/common.css" />
<script type="text/javascript" src="js/jquery-1.11.1.js"></script>
<script type="text/javascript">
$(function(){
$(".thumbs a").click(function(){
var largePath=$(this).attr("href");
var largeAlt=$(this).attr("title");
$("#largeImg").attr({
src:largePath,
alt:largeAlt
});
return false;
});
});
</script>
</head>
<body>
<form action="smartUploadServlet.do" method="post" enctype="multipart/form-data">
上传文件1:<input type="file" name="myfile1"/><br>
上传文件2:<input type="file" name="myfile2"/><br>
上传文件3:<input type="file" name="myfile3"/><br>
<input type="submit" value="提交"> ${result}
</form>
<hr>
下载：<a href="smartDownloadServlet.do?filename=img5-lg.jpg">img5-lg.jpg</a>
<hr>
<h2>图片预览</h2>
<p><img id="largeImg" src="images/img1-lg.jpg" alt="Large Image"/></p>
<p class="thumbs">
<a href="images/img2-lg.jpg" title="Image2"><img src="images/img2-thumb.jpg"></a>
<a href="images/img3-lg.jpg" title="Image3"><img src="images/img3-thumb.jpg"></a>
<a href="images/img4-lg.jpg" title="Image4"><img src="images/img4-thumb.jpg"></a>
<a href="images/img5-lg.jpg" title="Image5"><img src="images/img5-thumb.jpg"></a>
<a href="images/img6-lg.jpg" title="Image6"><img src="images/img6-thumb.jpg"></a>
</p>
</body>
</html>
下载部分的代码
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String filename = request.getParameter("filename");
SmartUpload su = new SmartUpload();
su.initialize(getServletConfig(), request, response);
su.setContentDisposition(null);
try {
su.downloadFile("/images/"+filename);
} catch (SmartUploadException e) {
e.printStackTrace();
}
}第三种方法Struts2实现上传下载
上传jsp页面代码：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP '03.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<link rel="stylesheet" type="text/css" href="css/common.css" />
<script type="text/javascript" src="js/jquery-1.11.1.js"></script>
<script type="text/javascript">
$(function(){
$(".thumbs a").click(function(){
var largePath=$(this).attr("href");
var largeAlt=$(this).attr("title");
$("#largeImg").attr({
src:largePath,
alt:largeAlt
});
return false;
});
});
</script>
</head>
<body>
<h2> 文件上传</h2>
<form action="upload.action" method="post" enctype="multipart/form-data">
上传文件1:<input type="file" name="upload"/><br>
上传文件2:<input type="file" name="upload"/><br>
上传文件3:<input type="file" name="upload"/><br>
<input type="submit" value="提交"> ${result}
</form>
<hr>
<h2>图片预览</h2>
<p><img id="largeImg" src="images/img1-lg.jpg" alt="Large Image"/></p>
<p class="thumbs">
<a href="images/img2-lg.jpg" title="Image2"><img src="images/img2-thumb.jpg"></a>
<a href="images/img3-lg.jpg" title="Image3"><img src="images/img3-thumb.jpg"></a>
<a href="images/img4-lg.jpg" title="Image4"><img src="images/img4-thumb.jpg"></a>
<a href="images/img5-lg.jpg" title="Image5"><img src="images/img5-thumb.jpg"></a>
<a href="images/img6-lg.jpg" title="Image6"><img src="images/img6-thumb.jpg"></a>
</p>
</body>
</html>struts.xml部分代码
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.3//EN"
"http://struts.apache.org/dtds/struts-2.3.dtd">
<struts>
<constant name="struts.enable.DynamicMethodInvocation" value="false" />
<constant name="struts.devMode" value="true" />
<!-- 国际化 -->
<constant name="struts.custom.i18n.resources" value="app"></constant>
<package name="default" namespace="/" extends="struts-default">
<action name="upload" class="com.lihf.action.FileUploadAction">
<result>/jsp/03.jsp</result>
<result name="input">/jsp/error.jsp</result>
<!-- 配置拦截器限制上传文件类型及大小 -->
<interceptor-ref name="fileUpload">
<param name="allowedTypes">image/bmp,image/x-png,image/gif,image/pjpeg</param>
<param name="maximumSize">2M</param>
</interceptor-ref>
<interceptor-ref name="defaultStack"></interceptor-ref>
</action>
<action name="download" class="com.lihf.action.DownLoadAction">
<param name="inputPath">/images/img2-lg.jpg</param>
<result name="success" type="stream">
<param name="contentType">application/octet-stream</param>
<param name="inputName">inputStream</param>
<!-- 以附件的形式下载 -->
<param name="contentDisposition">attachment;filename="${downloadFileName}"</param>
<param name="bufferSize">8192</param>
</result>
</action>
</package>
</struts>web.xml部分代码
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>scxz</display-name>
<servlet>
<servlet-name>UploadServlet</servlet-name>
<servlet-class>com.lihf.servlet.UploadServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>DownloadServlet</servlet-name>
<servlet-class>com.lihf.servlet.DownloadServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>SmartUploadServlet</servlet-name>
<servlet-class>com.lihf.servlet.SmartUploadServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>SmartDownloadServlet</servlet-name>
<servlet-class>com.lihf.servlet.SmartDownloadServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UploadServlet</servlet-name>
<url-pattern>/uploadServlet.do</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>DownloadServlet</servlet-name>
<url-pattern>/downloadServlet.do</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>SmartUploadServlet</servlet-name>
<url-pattern>/smartUploadServlet.do</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>SmartDownloadServlet</servlet-name>
<url-pattern>/smartDownloadServlet.do</url-pattern>
</servlet-mapping>
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>action方法：
package com.lihf.action;
import java.io.File;
import java.util.List;
import org.apache.commons.io.FileUtils;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;
public class FileUploadAction extends ActionSupport {
private List<File> upload;
private List<String> uploadContentType;
private List<String> uploadFileName;
private String result;
public List<File> getUpload() {
return upload;
}
public void setUpload(List<File> upload) {
this.upload = upload;
}
public List<String> getUploadContentType() {
return uploadContentType;
}
public void setUploadContentType(List<String> uploadContentType) {
this.uploadContentType = uploadContentType;
}
public List<String> getUploadFileName() {
return uploadFileName;
}
public void setUploadFileName(List<String> uploadFileName) {
this.uploadFileName = uploadFileName;
}
public String getResult() {
return result;
}
public void setResult(String result) {
this.result = result;
}
@Override
public String execute() throws Exception {
String path = ServletActionContext.getServletContext().getRealPath("/images");
File file = new File(path);
if(!file.exists()){
file.mkdir();
}
for(int i=0;i<upload.size();i++){
FileUtils.copyFile(upload.get(i), new File(file,uploadFileName.get(i)));
}
result ="上传成功!";
return SUCCESS;
}
}下载：
action方法：
package com.lihf.action;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import org.apache.commons.io.FileUtils;
import org.apache.struts2.ServletActionContext;
import com.opensymphony.xwork2.ActionSupport;
public class DownLoadAction extends ActionSupport {
public String inputPath;
public String fileName;
public String getFileName() {
return fileName;
}
public void setFileName(String fileName) {
this.fileName = fileName;
}
public String getInputPath() {
return inputPath;
}
public void setInputPath(String inputPath) {
this.inputPath = inputPath;
}
@Override
public String execute() throws Exception {
return SUCCESS;
}
public InputStream getInputStream() throws IOException{
String path = ServletActionContext.getServletContext().getRealPath("/images");
String filePath = path+"\\"+fileName;
File file = new File(filePath);
return FileUtils.openInputStream(file);
//根据文件路径获取流信息固定下载文件使用方法
//return ServletActionContext.getServletContext().getResourceAsStream(inputPath);
}
public String getDownloadFileName(){
//如果是中文的文件名称需要转码
String downloadFileName = "";
try {
downloadFileName = URLEncoder.encode("文件下载.jpg","UTF-8");
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return downloadFileName;
}
}
jsp页面：
<a href="download.action?fileName=img3-lg.jpg">文件下载(图片)</a>
扫一扫
被折叠的 条评论
为什么被折叠?
到【灌水乐园】发言
