javaweb实现文件的上传与下载，供大家参考，具体内容如下
第一步：导包
导入commons-fileupload-1.3.3.jar和commons-io-2.4.jar两个依赖包
第二步：编写前端页面
1、提交页面 index.jsp
<%@ page language="java" contenttype="text/html; charset=utf-8"
pageencoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
<form action="${pagecontext.request.contextpath }/fileupload" method="post" enctype="multipart/form-data">
头像：<input type="file" name="img" accept="image/*"/>
<input type="submit" value="提交"/>
</form>
</body>
</html>
2、结果页面 result.jsp
<%@ page language="java" contenttype="text/html; charset=utf-8"
pageencoding="utf-8"%>
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>insert title here</title>
</head>
<body>
<center>
<a href="${pagecontext.request.contextpath }/download?filename=${filename}" >
<img alt="xx" src="${src }">
</a>
</center>
</body>
</html>
第三步：编写上传和下载代码
1、上传图片 fileupload.java
package cn.yz123123.controller;
import java.io.file;
import java.io.fileoutputstream;
import java.io.ioexception;
import java.io.inputstream;
import javax.servlet.servletexception;
import javax.servlet.annotation.multipartconfig;
import javax.servlet.annotation.webservlet;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import javax.servlet.http.part;
@webservlet("/fileupload")
@multipartconfig
public class fileupload extends httpservlet {
private static final long serialversionuid = 1l;
protected void doget(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {
dopost(request, response);
}
protected void dopost(httpservletrequest request, httpservletresponse response) throws servletexception, ioexception {
//string username = request.getparameter("username");
part part = request.getpart("img");
//获取文件的真实名称
string header = part.getheader("content-disposition");
string realname = header.substring(header.indexof("filename=")+10, header.length()-1);
//获取文件自身流
inputstream inputstream = part.getinputstream();
//获取file真实路径，如果没有则创建
string dir = request.getservletcontext().getrealpath("/file/");
file dirfile = new file(dir);
//上面只是实例化了一个对象，并没有真正的创建一个文件夹
if (!dirfile.exists()) {
dirfile.mkdirs();
}
//创建文件对象，并用流的形式写在相应的文件夹中
file file = new file(dir, realname);
fileoutputstream fileoutputstream = new fileoutputstream(file);
byte[] buf = new byte[1024];
int len;
while((len=inputstream.read(buf))!=-1) {
fileoutputstream.write(buf, 0, len);
}
fileoutputstream.close();
inputstream.close();
//以下为测试
request.setattribute("src", request.getcontextpath()+"/file/"+realname);
request.setattribute("filename", realname);
request.getrequestdispatcher("/result.jsp").forward(request, response);
}
}
2、下载图片 filedownload.java
package cn.yz123123.controller;
import java.io.fileinputstream;
import java.io.ioexception;
import java.util.uuid;
import javax.servlet.servletexception;
import javax.servlet.servletoutputstream;
import javax.servlet.annotation.webservlet;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
@webservlet(urlpatterns = "/download")
public class filedownload extends httpservlet{
@override
protected void doget(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
string filename = req.getparameter("filename");
//获取文件的真实路径
string filepath = req.getservletcontext().getrealpath("/file/"+filename);
fileinputstream fileinputstream = new fileinputstream(filepath);
resp.setcharacterencoding("utf-8");
resp.setheader("content-disposition","attachment;filename="+uuid.randomuuid()+filename);
servletoutputstream outputstream = resp.getoutputstream();
byte[] buf = new byte[1024];
int len;
while((len=fileinputstream.read(buf))!=-1) {
outputstream.write(buf, 0, len);
}
outputstream.close();
fileinputstream.close();
}
@override
protected void dopost(httpservletrequest req, httpservletresponse resp) throws servletexception, ioexception {
super.doget(req, resp);
}
}
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