文件的上传与下载（一）

在实现文件上传和下载之前我们需要做一些准备工作，在Apache官网去下载文件上传下载的两个组件，下载链接这里给出：common-fileupload组件下载：http://commons.apache.org/proper/commons-fileupload/

common-io组件下载：http://commons.apache.org/proper/commons-io/根据自己需求下载对应版本

一、创建工程

将所需要的两个开发包导入到工程项目中如图：

二、代码编写

1.前端页面代码

1）. 在WebRoot目录下新建一个fileUpload.jsp页面，用来上传文件

 1 <%@ page language="java" import="java.util.*" pageEncoding="GB18030"%>
 2 <%
 3 String path = request.getContextPath();
 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 5 %>
 6 
 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 8 <html>
 9   <head>
10     <base href="<%=basePath%>">
11     
12     <title>My JSP 'fileUpload.jsp' starting page</title>
13     
14     <meta http-equiv="pragma" content="no-cache">
15     <meta http-equiv="cache-control" content="no-cache">
16     <meta http-equiv="expires" content="0">    
17     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
18     <meta http-equiv="description" content="This is my page">
19     <!--
20     <link rel="stylesheet" type="text/css" href="styles.css">
21     -->
22 
23   </head>
24   
25   <body>
26     <!-- 文件上传表单的提交方式必须是“post” 编码类型必须为：enctype="multipart/form-data" -->
27     <form action="UploadServlet" method="post" enctype="multipart/form-data">
28     
29         username: <input type="text" name="username" /><br>
30         file:  <input type="file" name="file"><br>
31         file2:  <input type="file" name="file2"><br>
32         <input type="submit" value="上传文件">
33     
34     </form>
35     
36   </body>
37 </html>

2）. 新建一个fileUploadResult.jsp页面用来显示结果信息

 1 <%@ page language="java" import="java.util.*,java.io.*" pageEncoding="GB18030"%>
 2 <%
 3 String path = request.getContextPath();
 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
 5 %>
 6 
 7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
 8 <html>
 9   <head>
10     <base href="<%=basePath%>">
11     
12     <title>My JSP 'fileUploadResult.jsp' starting page</title>
13     
14     <meta http-equiv="pragma" content="no-cache">
15     <meta http-equiv="cache-control" content="no-cache">
16     <meta http-equiv="expires" content="0">    
17     <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
18     <meta http-equiv="description" content="This is my page">
19     <!--
20     <link rel="stylesheet" type="text/css" href="styles.css">
21     -->
22 
23   </head>
24   
25   <body>
26     <%-- 
27     <%
28         //获取流对象
29         InputStream inputStream = request.getInputStream();
30         
31         BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
32         
33         String buffer = null;
34         
35         while((buffer = br.readLine()) != null){
36             out.print(buffer + "<br>");
37         }
38         
39         br.close();
40         inputStream.close();
41     
42      %>
43      --%>
44      ${message}<br>
45          
46      EL-username : ${requestScope.username} <br>
47      EL-file1  : ${requestScope.file }<br>
48      EL-file2 : ${requestScope.file2}<br>
49      
50   </body>
51 </html>

2. 编写上传文件处理的Servlet代码

1) UploadServlet.java代码如下：

  1 package com.Servlet;
  2 
  3 import java.io.File;
  4 import java.io.FileOutputStream;
  5 import java.io.IOException;
  6 import java.io.InputStream;
  7 import java.io.PrintWriter;
  8 import java.util.List;
  9 
 10 import javax.servlet.ServletException;
 11 import javax.servlet.http.HttpServlet;
 12 import javax.servlet.http.HttpServletRequest;
 13 import javax.servlet.http.HttpServletResponse;
 14 
 15 import org.apache.commons.fileupload.FileItem;
 16 import org.apache.commons.fileupload.disk.DiskFileItemFactory;
 17 import org.apache.commons.fileupload.servlet.ServletFileUpload;
 18 
 19 public class UploadServlet extends HttpServlet {
 20 
 21     /**
 22      * The doPost method of the servlet. <br>
 23      *
 24      * This method is called when a form has its tag value method equals to post.
 25      * 
 26      * @param request the request send by the client to the server
 27      * @param response the response send by the server to the client
 28      * @throws ServletException if an error occurred
 29      * @throws IOException if an error occurred
 30      */
 31     public void doPost(HttpServletRequest request, HttpServletResponse response)
 32             throws ServletException, IOException {
 33 
 34         
 35         //得到上传文件的保存目录，将上传的文件放在webRoot目录下（但是一般为了安全放在WEB-INF目录下，不允许外界直接访问，保证上传的安全）
 36         String path = this.getServletContext().getRealPath("/upload");
 37         
 38         File file = new File(path);
 39         
 40         //判断上传文件的保存目录是否存在
 41         if(!file.exists() && !file.isDirectory()){
 42             System.out.println(path + "目录不存在，需要创建！");
 43             //创建目录
 44             file.mkdir();
 45         }
 46         //消息提示
 47         String message = "";
 48         try{
 49             //使用Apache文件上传组件处理文件上传步骤：
 50             //1.创建一个DiskFileItemFactory工厂
 51             DiskFileItemFactory factory = new DiskFileItemFactory();
 52             //2.创建一个文件上传解析器
 53             ServletFileUpload upload = new ServletFileUpload(factory);
 54             //解决中文乱码
 55             upload.setHeaderEncoding("UTF-8");
 56             //3.判断提交的数据普通表单的数据还是带文件上传的表单
 57             if(!upload.isMultipartContent(request)){
 58                 //如果是表单数据普通表单,则按照传统方式获取数据
 59                 return ;                
 60             }
 61             //4.使用ServletFileUpload解析器解析上传数据，解析结果返回的是一个List<FileItem>集合，每一个FileItem对应一个Form表单的输入项
 62             List<FileItem> list = upload.parseRequest(request);
 63             for(FileItem item : list){
 64                 //如果fileItem中封装的是普通输入项的数据
 65                 if(item.isFormField()){
 66                     //获取字段名字
 67                     String name = item.getFieldName();
 68                     //解决普通输入项中中文乱码问题
 69                     String value = item.getString("UTF-8");//value = new String(value.getBytes("iso8859-1"),"UTF-8");
 70                     System.out.println(name + " = " + value);
 71                 }else{    //如果表单中提交的是上传文件
 72                     //获得上传的文件名称
 73                     String filename = item.getName();
 74                     System.out.println(filename);
 75                     if(filename == null || filename.trim().equals(" ")){
 76                         continue;
 77                     }
 78                     //注意：不同的浏览器提交的文件名称是不一样的，有些浏览器提交的文件会带有路径，如“D:\projectWebRoothello.jsp”，有一些是单纯的文件名：hello.jsp
 79                     //去掉获取到文件名中的路径名，保留单纯的文件名
 80                     filename = filename.substring(filename.lastIndexOf("\") + 1);
 81                     //获取item中的上传文件的输入流
 82                     InputStream in = item.getInputStream();
 83                     //创建一个文件输入流
 84                     FileOutputStream out = new FileOutputStream(path + "\" + filename);
 85                     //创建一个缓冲区
 86                     byte buffer[] = new byte[1024];
 87                     //判断输入流中的数据是否已经读取完毕的标志位
 88                     int len = 0;
 89                     //循环将输入流读入到缓冲区当中，（len = in.read(buffer)>0）就表示in里面还有数据存在
 90                     while((len = in.read(buffer)) > 0){
 91                         //使用FileOutputStream输出流将缓冲区的数据写入到指定的目录（path+"\"+filename）当中
 92                         out.write(buffer, 0, len);
 93                     }
 94                     //关闭输入流
 95                     in.close();
 96                     //关闭输出流
 97                     out.close();
 98                     //删除处理文件上传生成的临时文件
 99                     item.delete();
100                     message = "文件上传成功!";
101                     
102                     
103                 }
104             }
105             
106         }catch(Exception e){
107             message = "文件上传失败！";
108             e.printStackTrace();
109         }
110         
111         request.setAttribute(message, message);
112         request.getRequestDispatcher("fileUploadResult.jsp").forward(request, response);
113         
114     }
115 
116 }

2）web.xml文件中的配置

 1 <?xml version="1.0" encoding="UTF-8"?>
 2 <web-app version="3.0"
 3     xmlns="http://java.sun.com/xml/ns/javaee"
 4     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 5     xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
 6   <servlet>
 7     
 8     <servlet-name>UploadServlet</servlet-name>
 9     <servlet-class>com.Servlet.UploadServlet</servlet-class>
10   </servlet>
11 
12   <servlet-mapping>
13     <servlet-name>UploadServlet</servlet-name>
14     <url-pattern>/UploadServlet</url-pattern>
15   </servlet-mapping>
16 
17 </web-app>

结果：

摘自：https://www.cnblogs.com/xdp-gacl/p/4200090.html