Jsp+Servlet实现文件上传下载

使用Servlet获取上传文件的输入流然后再解析里面的请求参数。

一、 Jsp页面

post方式提交，enctype为”multipart/form-data”。

<body>
<form action="uploadServlet.do" method="post" enctype="multipart/form-data">
<input type="file" id="myfile" name="myfile">
<input type="submit" value="提交">
<br>
    ${result}
<br>
    下载：<a href="downloadServlet.do?filename=file.txt">file.txt</a>
<br>
    ${errorResult}

</form>
</body>

二、创建文件上传Servlet

上传的文件无法直接保存，需创建一个临时文件，获取上传文件输入流信息，将文件输出流指向临时文件。从临时文件获取上传文件名、文件内容开始与结束指针，设置文件上传的路径，临时文件将文件内容输出到保存文件。

package com.yf.servlet;

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 UploadServlet extends HttpServlet {

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
this.doPost(request, response);

    }


public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
            System.out.println("已接收到请求 ");
//从request当中获取流信息
            InputStream fileSource = request.getInputStream();
            String tempFileName = "E:/tempFile";
//tempFile指向临时文件
            File tempFile = new File(tempFileName);
//outputStream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();//第一行不要
//获取第二行
            String str = randomFile.readLine();
int benginIndex = str.lastIndexOf("=")+2;
int endIndex = str.lastIndexOf("\"");
            String fileName = str.substring(benginIndex,endIndex);
            System.out.println("文件名"+fileName);

//重新定位文件指针到文件头
            randomFile.seek(0);
long startPosition = 0;
int i = 1;
while((n = randomFile.readByte())!= -1 &&i <= 4){
if(n == '\n'){
//重新获取文件指针
                    startPosition = randomFile.getFilePointer();
                    i++;
                }
            }
            startPosition -=1;
//获取文件内容结束位置
//定位指针到文件结尾
            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 -= 1;

//设置保存文件的路径
            String realPath = getServletContext().getRealPath("/")+"images";
            File fileupload = new File(realPath);
if(!fileupload.exists()){
//不存在创建
                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
            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();
            request.setAttribute("result", "上传成功");
            RequestDispatcher dispatcher = request.getRequestDispatcher("index.jsp");
            dispatcher.forward(request, response);
    }


}

三、创建文件下载Servlet

package com.yf.servlet;

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

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 {


public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

this.doPost(request, response);
    }


public void doPost(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+"\"");
//读取文件
            InputStream inputStream = new FileInputStream(file);
            ServletOutputStream outputStream = response.getOutputStream();
byte b[] = new byte[1024];
int n;
while((n = inputStream.read(b))!=-1){
                outputStream.write(b,0,n);
            }
//关闭流
            outputStream.close();
            inputStream.close();

        }else{
            request.setAttribute("errorResult", "文件不存在下载失败");
            request.getRequestDispatcher("index.jsp").forward(request, response);
        }
    }



}

四、运行结果

选择上传文件：

Jsp+Servlet实现文件上传下载

点击提交
在tomcat下保存文件，页面显示上传成功。

Jsp+Servlet实现文件上传下载

点击下载，如果文件存在，则下载。不存在显示下载失败。

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Jsp+Servlet实现文件上传下载

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