通过JSP+servlet实现文件上传功能

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"/>
               &nbsp;&nbsp;<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);
    }
}