使用JSP和Servlet实现文件上传下载-优快云博客

本文介绍如何在动态Web项目中使用JSP和Servlet进行文件上传和下载操作。首先创建项目目录结构，包括img、js、css、jsp等文件夹。首页用于展示，接着创建两个Servlet，一个负责文件上传，另一个处理文件下载。别忘了在Tomcat的XML配置文件中进行相应的设置。

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先建一个dynamic web project ,然后在webcontent下建立文件夹img js css jsp等构建网站目录

like this

然后我们这里使用的是最原始的也是最实在的jsp+servlet来写的，目录中的首页是用来显示的

首页：

<%@ 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 + '" />').show();
			}).mouseout(function(){
				la.hide();
			});
		});	
		/*  //使用js实现文件上传图片的预览
		function showPreview(obj){
			var str = obj.value;
			document.getElementById("previewImg").innerHTML = 
				"<img src = '" + str + "' />";
		}
		*/
	</script>
  </head>
  
  <body>

  	  <img id="previewImg" src="images/preview.jpg" width="80" height="80" />
  	 <form action="uploadServlet.do" method="post" enctype="multipart/form-data">
  		请选择图片：<input id="myfile" name="myfile" type="file" onchange="showPreview(this)"/>
  		<input type="submit" value="提交"  />${result}
  	</form>
  	下载：<a href="downloadServlet.do?filename=test1.txt">test1.txt</a>    ${errorResult}
  	
  	<div id="large"></div>
  	
  	<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>

这里的css文件和jquery文件没有上传，jquery-1.11.1.js和common.css

然后分别新建两个servlet分别是上传和下载，

UploadServlet:

package com.upload.servlet;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class UploadServlet extends HttpServlet {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doPost(req,resp);
	}

	public void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		//从request当中获取流信息
		InputStream fileSource = req.getInputStream();
		String tempFileName = "D:/tempFile";
		//tempFile指向临时文件
		File tempFile = new File(tempFileName);
		//outputStram文件输出流指向这个临时文件
		FileOutputStream outputStream = new FileOutputStream(tempFile);
		byte b[] = new byte[1024];
		int n;
		while(( n = fileSource.read(b)) != -1){
			outputStream.write(b, 0, n);
		}
		//关闭输出流、输入流
		outputStream.close();
		fileSource.close();
		
		//获取上传文件的名称
		RandomAccessFile randomFile = new RandomAccessFile(tempFile,"r");
		randomFile.readLine();
		String str = randomFile.readLine();
		int beginIndex = str.lastIndexOf("\\") + 1;
		int endIndex = str.lastIndexOf("\"");
		String filename = str.substring(beginIndex, endIndex);
		System.out.println("filename:" + filename);
		
		//重新定位文件指针到文件头
		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;
		//获取文件内容 结束位置
		randomFile.seek(randomFile.length());
		long endPosition = randomFile.getFilePointer();
		int j = 1;
		while(endPosition >=0 && j<=2){
			endPosition--;
			randomFile.seek(endPosition);
			if(randomFile.readByte() == '\n'){
				j++;
			}
		}
		endPosition = endPosition -1;
		
		//设置保存上传文件的路径
		String realPath = getServletContext().getRealPath("/") + "images";
		System.out.println(realPath);
		//String realPath="D:/";
		File fileupload = new File(realPath);
		if(!fileupload.exists()){
			fileupload.mkdir();
		}
		File saveFile = new File(realPath,filename);
		RandomAccessFile randomAccessFile = new RandomAccessFile(saveFile,"rw");
		//从临时文件当中读取文件内容（根据起止位置获取）
		randomFile.seek(startPosition);
		while(startPosition < endPosition){
			randomAccessFile.write(randomFile.readByte());
			startPosition = randomFile.getFilePointer();
		}
		//关闭输入输出流、删除临时文件
		randomAccessFile.close();
		randomFile.close();
		tempFile.delete();
		
		req.setAttribute("result", "上传成功！");
		RequestDispatcher dispatcher = req.getRequestDispatcher("jsp/01.jsp");
		dispatcher.forward(req, resp);
	}
}

DownloadServlet:

package com.upload.servlet;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class DownloadServlet extends HttpServlet {

	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	public void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		//获取文件下载路径
		String path = getServletContext().getRealPath("/") + "images\\";
		String filename = req.getParameter("filename");
		System.out.println(path+filename);
		File file = new File(path + filename);
		if(file.exists()){
			//设置相应类型application/octet-stream
			resp.setContentType("application/x-msdownload");
			//设置头信息
			resp.setHeader("Content-Disposition", "attachment;filename=\"" + filename + "\"");
			InputStream inputStream = new FileInputStream(file);
			ServletOutputStream ouputStream = resp.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{
			req.setAttribute("errorResult", "文件不存在下载失败！");
			RequestDispatcher dispatcher = req.getRequestDispatcher("jsp/01.jsp");
			dispatcher.forward(req, resp);
		}
		
		
	}

	public void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		doGet(req,resp);
	}

}

均包含在com.upload.servlet 包中

最重要的，别忘了xml的配置，在tomcat7.0中xml好像是自己不给配置的，这里我也只能手动配置了2333，找到文件夹加入xml文件

<?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"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0">
	<servlet>
		<servlet-name>UploadServlet</servlet-name>
		<servlet-class>com.upload.servlet.UploadServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>UploadServlet</servlet-name>
		<url-pattern>/uploadServlet.do</url-pattern>
	</servlet-mapping>
	<servlet>
		<servlet-name>DownloadServlet</servlet-name>
		<servlet-class>com.upload.servlet.DownloadServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>DownloadServlet</servlet-name>
		<url-pattern>/downloadServlet.do</url-pattern>
	</servlet-mapping>
	<display-name>shangchuan</display-name>
	<welcome-file-list>
		<welcome-file>index.html</welcome-file>
		<welcome-file>index.htm</welcome-file>
		<welcome-file>index.jsp</welcome-file>
		<welcome-file>default.html</welcome-file>
		<welcome-file>default.htm</welcome-file>
		<welcome-file>default.jsp</welcome-file>
	</welcome-file-list>
</web-app>

一般的，404或者是什么什么full request问题首先要检查文档路径（这个占多数）和xml的配置
common.css补充：

body {
	margin: 20px auto;
	padding: 0;
	width: 580px;
	font: 75%/120% Arial, Helvetica, sans-serif;
	text-align: center;
}

h2 {
	font: bold 190%/100% Arial, Helvetica, sans-serif;
	margin: 0 0 .2em;
}

h2 em {
	font: normal 80%/100% Arial, Helvetica, sans-serif;
	color: #999999;
}

#largeImg {
	border: solid 1px #ccc;
	width: 550px;
	height: 400px;
	padding: 5px;
}

.thumbs img {
	border: solid 1px #ccc;
	width: 100px;
	height: 100px;
	padding: 4px;
}

.thumbs img:hover {
	border-color: #FF9900;
}

#large {
	position: absolute;
	z-index: 999;
}