Java初学者：文件的上传和下载

最新推荐文章于 2025-03-11 00:15:00 发布

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本文介绍了使用Java实现文件上传和下载的方法。通过JSP页面和Servlet处理文件上传，并将文件信息存储到数据库中。同时提供了文件下载的功能。

Java初学者：文件的上传和下载

　　　学过文件上传下载之后，简单的来体会一下所学知识。

jsp展示

1.upload.jsp

<%@ 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>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">

</head>

<body>
    This is my JSP page. <br>

    <form action="uploadServlet" method="post" enctype="multipart/form-data">
    <p>请选择文件<input type="file" name="file"></p>
    <p><input type="submit" value="提交"/></p>
    </form>
</body>
</html>

对于上传文件的处理

2.uploadServlet

package servlet;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

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

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

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 {
  //实例化磁盘文件解析工厂
  DiskFileItemFactory dfif = new DiskFileItemFactory();
  //实例化解析对象
  ServletFileUpload sfu = new ServletFileUpload(dfif);
  String filename =null;
  InputStream is=null;
  FileOutputStream fos=null;

  //解析请求信息
  try {
   List<FileItem> list = sfu.parseRequest(request);
   //找到form中上传的文件
   for(FileItem fi : list){
    if(!fi.isFormField()){
     is = fi.getInputStream();
     //截取文件名，放入指定的文件目录下
     filename = fi.getName();
     filename = filename.substring(filename.lastIndexOf("\\")+1);
     fos = new FileOutputStream("D:\\javajava\\upload\\"+filename);//个人设定的所要下载的文件目录
     //写入到指定文件
     byte[] b = new byte[512];
     int i;
     while((i=is.read(b))!=-1){
      fos.write(b);
     }
     //将文件名保存到数据库
     insert(filename);
    }
   }
   List namelist = getFileName();
   request.getSession().setAttribute("namelist", namelist);
   request.getRequestDispatcher("jsp/download.jsp").forward(request, response);
  } catch (FileUploadException e) {
   e.printStackTrace();
  }finally{
   fos.close();
   is.close();
  }

}

//将文件名称存储到数据库
public boolean insert(String str){
  try{
   Class.forName("com.mysql.jdbc.Driver");
   Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mytest?useUnicode=true&characterEncoding=utf-8","root","root");
   PreparedStatement ps = conn.prepareStatement("insert into filename(name) values(?) ");
   ps.setString(1, str);
   int n=0;
   if((n=ps.executeUpdate())>0){
    return true;
   }
   ps.close();
   conn.close();
  } catch (Exception e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  return false;

}
@SuppressWarnings("null")

//从数据库中得到所有上传的文件名称
public List getFileName(){
  List list=new ArrayList();
  try {
   Class.forName("com.mysql.jdbc.Driver");
   Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mytest?useUnicode=true&characterEncoding=utf-8","root","root");
   PreparedStatement ps = conn.prepareStatement("select * from filename");
   ResultSet rs = ps.executeQuery();
   while(rs.next()){
    String str=rs.getString(2);
    list.add(str);
   }
   rs.close();
   ps.close();
   conn.close();
  } catch (Exception e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
  return list;

}

}

3.下载页面的jsp展示

download.jsp

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
    <base href="<%=basePath%>">

    <title>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">

</head>

<body>
    <font size="10" >您可以下载以下文件：</font>
    <%
    List list = (List)session.getAttribute("namelist");
    String str=null;
    for(int i=0;i<list.size();i++){
    str = (String)list.get(i);
     %>
     <a href="downloadServlet?filename=<%=str %>"> <%=str %></a>

    <%} %>
</body>
</html>

4.文件下载的后端处理

package servlet;

import java.io.FileInputStream;
import java.io.IOException;
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 {

/**
* The doGet method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to get.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

this.doPost(request, response);
}

/**
* The doPost method of the servlet. <br>
*
* This method is called when a form has its tag value method equals to post.
*
* @param request the request send by the client to the server
* @param response the response send by the server to the client
* @throws ServletException if an error occurred
* @throws IOException if an error occurred
*/
public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  System.out.print("here");
  request.setCharacterEncoding("utf-8");
  String filename = request.getParameter("filename");

  response.setContentType("multipart/form-data");
  response.setHeader("Content-Disposition", "attachment;filename="+filename);
  FileInputStream fis = new FileInputStream("D:\\javajava\\upload\\"+filename);
  ServletOutputStream sos = response.getOutputStream();
  byte[] b = new byte[512];
  int i;

  while((i=fis.read(b))!=-1){
   sos.write(b);
  }

  fis.close();
  sos.close();
}