在TCP/IP中，最早出现的文件上传机制是FTP.它将文件由客户端到服务器的标准机制。
但是在JSP中不能使用FTP来上传文件，这是有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，在接受此请求的servlet中的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。
代码分两部分
part1:前台页面index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%> <html> <head> </head> <body> <form action="UploadFile" method="post" enctype="multipart/form-data"> <table> <tr> <td align="center"> 请选择上传的文件:<input type="file" name="fileName"/>
<input type="submit" value="上传"/>${result}
</td> </tr> </table> </form> </body> </html>
part2:servlet代码
package com.file; import java.io.File; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; 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 UploadFile extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //写入缓存文件 InputStream fileSource=request.getInputStream(); String tempFileName="E:/tempFile"; File tempFile=new File(tempFileName); FileOutputStream outputStram=new FileOutputStream(tempFile); byte[] b=new byte[1024]; int n; while((n=fileSource.read(b))!=-1){ outputStram.write(b,0,n); } outputStram.close(); fileSource.close(); System.out.println("成功"); //获取文件名 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);
//获取上传文件内容的开始位置 randomFile.seek(0); long startPosition=0; int i=1; while((n=randomFile.readByte())!=-1&&i<=4){ if(n==' '){ startPosition=randomFile.getFilePointer(); i++; } } startPosition=startPosition-1;
//获取上传文件内容的结束位置
randomFile.seek(randomFile.length()); long endPosition=randomFile.getFilePointer(); int j=1; while(endPosition>=0&&j<=2){ endPosition--; randomFile.seek(endPosition); if(randomFile.readByte()==' '){ j++; } } endPosition=endPosition-1;
//上传文件
String path=getServletContext().getRealPath("/")+"MyImages"; //指定上传文件的目录
File fileupload=new File(path); if(!fileupload.exists()){ fileupload.mkdir(); } File saveFile=new File(path,filename); RandomAccessFile RAF=new RandomAccessFile(saveFile,"rw"); randomFile.seek(startPosition); while(startPosition<endPosition){ RAF.write(randomFile.readByte()); startPosition=randomFile.getFilePointer(); } RAF.close(); randomFile.close(); tempFile.delete(); request.setAttribute("result","上传成功!"); RequestDispatcher dispatcher=request.getRequestDispatcher("index.jsp"); dispatcher.forward(request,response); } }