文件的上传与下载---------------------待补充

一：文件上传

1.表单需要的准备一知识点

　　请求方式为post，不方便使用get

　　使用file表单域，type=“file”

　　使用的编码方式是二进制，enctype=“multipart/form-data”

　　　　表单的默认值是application/x-www-form-urlencoded，试用与少量的字符集。

2.服务端准备

　　不能使用request.getParamete获取信息，因为编码方式已经改了。

　　可以使用输入流的方式，但是不建议

　　具体使用commons-fileupload完成上传操作

3.加入两个jar包

　　commons-fileupload-1.3.3.jar

　　commons-io-2.5.jar

4.基本思想

　　commons-fileupload：

　　　　可以解析请求，得到FileItem对象组成的List

　　　　把所有的请求信息都解析为FileItem对象，无论是文本域还是文件域

　　　　可以调用FileItem的isFormField方法判断是一个表单域或不是一个表单域

　　　　再进一步获取信息

二：helloUpload程序

1.upload.jsp

 1 <%@ page language="java" contentType="text/html; charset=utf-8"
 2     pageEncoding="utf-8"%>
 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 4 <html>
 5 <head>
 6 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 7 <title>Insert title here</title>
 8 </head>
 9 <body>
10     <form action="uploadServlet" method="post" enctype="multipart/form-data">
11         File:<input type="file" name="file"/>
12         <br><br>
13         Desc:<input type="text" name="desc"/>
14         <br>
15         <input type="submit" value="Submit">
16     </form>
17 </body>
18 </html>

2.UploadServlet.java

 1 package com.web;
 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.OutputStream;
 8 import java.util.List;
 9 
10 import javax.servlet.ServletException;
11 import javax.servlet.annotation.WebServlet;
12 import javax.servlet.http.HttpServlet;
13 import javax.servlet.http.HttpServletRequest;
14 import javax.servlet.http.HttpServletResponse;
15 
16 import org.apache.commons.fileupload.FileItem;
17 import org.apache.commons.fileupload.FileUploadException;
18 import org.apache.commons.fileupload.disk.DiskFileItemFactory;
19 import org.apache.commons.fileupload.servlet.ServletFileUpload;
20 
21 
22 @WebServlet("/uploadServlet")
23 public class UploadServlet extends HttpServlet {
24     
25     private static final long serialVersionUID = 1L;
26 
27     protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
28         DiskFileItemFactory factory=new DiskFileItemFactory();
29         factory.setSizeThreshold(1024*1024*7);
30         File tempDirectory=new File("d:\tempDirectory");
31         factory.setRepository(tempDirectory);
32         
33         ServletFileUpload upload=new ServletFileUpload(factory);
34         upload.setSizeMax(1024*1024*5);
35         try {
36             List<FileItem> items=upload.parseRequest(request);
37             for(FileItem item : items) {
38                 if(item.isFormField()) {
39                     String name=item.getFieldName();
40                     String value=item.getString();
41                     System.out.println(name+"==="+value);
42                 }else {
43                     String fieldName=item.getFieldName();
44                     String fileName=item.getName();
45                     
46                     //获取不带路径的文件名
47                     int start = fileName.lastIndexOf("\");  
48                     String fileName2 = fileName.substring(start+1);
49                     
50                     String contentType=item.getContentType();
51                     boolean isInMemory=item.isInMemory();
52                     long sizeInBytes=item.getSize();
53                     System.out.println(fieldName);
54                     System.out.println(fileName);
55                     System.out.println(fileName2);
56                     System.out.println(contentType);
57                     System.out.println(isInMemory);
58                     System.out.println(sizeInBytes);
59                     
60                     InputStream in=item.getInputStream();
61                     byte[] buffer=new byte[1024];
62                     int len=0;
63                     fileName2="d:\files\"+fileName2;
64                     System.out.println(fileName2);
65                     OutputStream out=new FileOutputStream(fileName2);
66                     while((len=in.read(buffer))!=-1) {
67                         out.write(buffer, 0, len);
68                     }
69                     out.close();
70                     in.close();
71                 }
72             }
73         } catch (FileUploadException e) {
74             e.printStackTrace();
75         }
76     }
77 
78 }

3.结果

三：应用

1.需求

　　上传

　　　　在页面上使用jquery实现新增一个附件，删除附件，但是需要保留一个

　　　　对文件的扩展名与文件的大小进行验证，若是出现错误，在页面上显示错误信息，如果通过验证，文件上传后文件名不能重复，在对应的数据表中增加一条记录

　　下载

2.添加jquery的包

　　jquery-1.7.2.js

3.项目目录

4.upload.jsp

 1 <%@ page language="java" contentType="text/html; charset=utf-8"
 2     pageEncoding="utf-8"%>
 3 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 4 <html>
 5 <head>
 6 <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
 7 <title>Insert title here</title>
 8 <script type="text/javascript" src="jquery-1.7.2.js"></script>
 9 <script type="text/javascript">
10 $(function(){
11     
12     var i = 2;
13     
14     $("#addFile").click(function(){
15         //添加
16         $(this).parent().parent().before("<tr class='file'><td>File"
17                 +i+":</td><td><input type='file' name='file"
18                 +i+"'</td></tr>"
19                 +"<tr class='desc'><td>Desc"
20                 +i+":</td><td><input type='text' name='desc"
21                 +i+"'/><button id='delete"
22                 +i+"'>删除</button></td></tr>");
23         i++;
24         //删除
25         $("#delete"+(i-1)).click(function(){
26             var $tr=$(this).parent().parent()
27             $tr.prev("tr").remove()
28             $tr.remove()
29             //对i进行排序
30             $(".file").each(function(index){
31                 $(this).find("td:first").text("File"+(index+1))
32                 $(this).find("td:last input").attr("name","file"+(index+1))
33             });
34             $(".desc").each(function(index){
35                 $(this).find("td:first").text("Desc"+(index+1))
36                 $(this).find("td:last input").attr("name","desc"+(index+1))
37             })
38         })
39         
40         return false;
41     })
42 });
43 </script>
44 </head>
45 <body>
46     <font color="red">${message }</font>
47     <br><br>    
48     <form action="fileuploadservlet" method="post" enctype="multipart/form-data">
49         
50         <table>
51             <tr class="file">
52                 <td>File1:</td>
53                 <td><input type="file" name="file1"/></td>
54             </tr>
55             <tr class="desc">
56                 <td>Desc1:</td>
57                 <td><input type="text" name="desc1"/></td>
58             </tr>
59             
60             <tr>
61                 <td><input type="submit" id="submit" value="提交"/></td>
62                 <td><button id="addFile">新增一个附件</button></td>
63             </tr>
64         </table>
65         
66     </form>
67 </body>
68 </html>

5.效果图

6.配置文件upload.properties

1 exts=pptx,docx,doc
2 file.max.size=1048576
3 total.file.max.size=5242880

7.对properties操作的工具类FileUploadAppProperties.java

 1 package com.web.app.utils;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 
 6 public class FileUploadAppProperties {
 7     private FileUploadAppProperties() {}
 8     
 9     private static Map<String,String> properties=new HashMap<>();
10     
11     private static FileUploadAppProperties instance=new FileUploadAppProperties();
12     
13     public  static FileUploadAppProperties getInstance() {
14         return instance;
15     }
16     
17     public static void addProperty(String propertyName,String propertyValue) {
18         properties.put(propertyName, propertyValue);
19     }
20     
21     public static String getProperty(String propertyName) {
22         return properties.get(propertyName);
23     }
24 }

8.使用监听器进行初始化FileUploadAppListener.java

 1 package com.web.app.listener;
 2 
 3 import java.io.InputStream;
 4 import java.util.Map;
 5 import java.util.Properties;
 6 
 7 import javax.servlet.ServletContextEvent;
 8 import javax.servlet.ServletContextListener;
 9 import javax.servlet.annotation.WebListener;
10 
11 import com.web.app.utils.FileUploadAppProperties;
12 
13 @WebListener
14 public class FileUploadAppListener implements ServletContextListener {
15 
16     public FileUploadAppListener() {
17         
18     }
19 
20     public void contextInitialized(ServletContextEvent arg0)  { 
21         InputStream in=getClass().getClassLoader().getResourceAsStream("/upload.properties");
22         Properties properties=new Properties();
23         try {
24             properties.load(in);
25             for(Map.Entry<Object, Object> pro:properties.entrySet()) {
26                 String propertyName=(String) pro.getKey();
27                 String propertyValue=(String) pro.getValue();
28                 FileUploadAppProperties.getInstance().addProperty(propertyName, propertyValue);
29             }
30         } catch (Exception e) {
31             e.printStackTrace();
32         }
33         
34     }
35     
36     public void contextDestroyed(ServletContextEvent arg0)  { 
37          
38     }
39 
40 }

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原文地址：https://www.cnblogs.com/juncaoit/p/7629286.html