• Javaweb项目中文件的上传与下载

    文件上传：将本地文件通过流的方式上传到服务器，常用的文件上传方法有很多，本次主要介绍的文件上传技术是FileUpLoad.文件上传三要素：1、表单提交方式为post.  2、需要有属性,name元素和值。3、表单enctype="multipart/form-data"。文件下载：将服务器的文件通过流写到客户端。文件下载的方式主要为超链接下载和手动编写代码方式下载。

    目录

    1、文件上传入门

    2-JS控制多个文件上传

    3-防止上传重名文件覆盖问题

    4-文件下载之超链接方式

    5-文件下载之手动编写Servlet方式

    6-文件下载之防止浏览器不同下载乱码问题

    7-指定目录的文件下载案例

    1、文件上传入门

    首先创建web项目，配置tomcat服务器，导入文件上传所需jar包，具体如下：

    web项目中创建文件上传的upload.jsp页面，具体如下：

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: nuist__NJUPT
    4.   Date: 2022-08-15
    5.   Time: 16:53
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <html>
    10. <head>
    11.     <title>Titletitle>
    12. head>
    13. <body>
    14. <form action="${pageContext.request.contextPath}/UploadServlet" method="post" enctype="multipart/form-data">
    15.     文件描述:<input type="text" name="info">br>
    16.     文件上传:<input type="file" name="upload">br>
    17.     <input type="submit" value="文件上传">
    18. form>
    19. body>
    20. html>

    处理upload.jsp表单提交的Servlet类，具体如下：

    1. import org.apache.commons.fileupload.FileItem;
    2. import org.apache.commons.fileupload.FileUploadException;
    3. import org.apache.commons.fileupload.disk.DiskFileItemFactory;
    4. import org.apache.commons.fileupload.servlet.ServletFileUpload;
    5.  
    6. import javax.servlet.ServletException;
    7. import javax.servlet.http.HttpServlet;
    8. import javax.servlet.http.HttpServletRequest;
    9. import javax.servlet.http.HttpServletResponse;
    10. import java.io.*;
    11. import java.util.List;
    12.  
    13. public class UploadServlet extends HttpServlet {
    14.     @Override
    15.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    16.         boolean flag = ServletFileUpload.isMultipartContent(req) ;
    17.         if(!flag){
    18.             //如果表单不是enctype="multipart/form-data"
    19.             req.setAttribute("msg","表单设置不正确");
    20.             req.getRequestDispatcher("/jsp/upload.jsp").forward(req,resp);
    21.         }
    22.         try {
    23.            //1.创建磁盘文件项工厂
    24.             DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
    25.             diskFileItemFactory.setSizeThreshold(3*1024*1024); //设置缓冲区的大小为3MB
    26.             //设置文件的临时路径
    27.             String temp = getServletContext().getRealPath("/temp") ;
    28.             diskFileItemFactory.setRepository(new File(temp));
    29.             //2.创建一个核心解析类
    30.             ServletFileUpload fileUpload = new ServletFileUpload(diskFileItemFactory) ;
    31.             //设置上传文件的大小为5MB
    32. //            fileUpload.setSizeMax(5*1024*1024);
    33.             //3.利用核心类解析Request，解析后会得到多个部分,存入list集合中
    34.             List list =  fileUpload.parseRequest(req) ;
    35.             //4.遍历文件项,判断文件项是普通项,还是文件上传项
    36.             for(FileItem fileItem : list){
    37.                 if(fileItem.isFormField()){
    38.                     //接收普通项的值
    39.                     String name = fileItem.getFieldName() ;
    40.                     String value = fileItem.getString("UTF-8") ;
    41.                     System.out.println(name + "   "+ value);
    42.                 }else{
    43.                     //文件上传项目
    44.                     //获得文件上传项的文件名及文件内容
    45.                     String filename = fileItem.getName() ;
    46.                     int index = filename.lastIndexOf("\\") ;
    47.                     if(index != -1){
    48.                         //老版本浏览器
    49.                         filename = filename.substring(index+1) ;
    50.                     }
    51.                     InputStream is = fileItem.getInputStream() ;
    52.                     //获得文件上传的磁盘绝对路径
    53.                     String realPath = getServletContext().getRealPath("/upload");
    54.                     //创建一个输出流,写入到真实的路径中
    55.                     OutputStream os = new FileOutputStream(realPath+"/"+filename) ;
    56.                     //两个流实现对接
    57.                     int len = 0 ;
    58.                     byte [] bytes = new byte[1024] ;
    59.                     while((len=is.read(bytes)) != -1){
    60.                         os.write(bytes,0,len);
    61.                     }
    62.                     is.close();
    63.                     os.close();
    64.                 }
    65. //                fileItem.delete(); //删除临时文件
    66.             }
    67.         } catch (FileUploadException e) {
    68.             e.printStackTrace();
    69.         }
    70.     }
    71.  
    72.     @Override
    73.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    74.         doGet(req,resp);
    75.     }
    76. }

    在web.xml文件中对使用的Servlet的名称及路径进行配置，具体如下：

    2. <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    3.          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    4.          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
    5.          version="4.0">
    6.     <servlet>
    7.     <servlet-name>UploadServletservlet-name>
    8.     <servlet-class>com.controller.UploadServletservlet-class>
    9.     servlet>
    10.     <servlet-mapping>
    11.         <servlet-name>UploadServletservlet-name>
    12.         <url-pattern>/UploadServleturl-pattern>
    13.     servlet-mapping>
    14.     
    15. web-app>

    2-JS控制多个文件上传

    JavaScript控制多个文件上传，在原来的基础上，编写多文件上传页面jsp如下：

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: nuist__NJUPT
    4.   Date: 2022-08-15
    5.   Time: 16:53
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <html>
    10. <head>
    11.     <title>Titletitle>
    12.     <script>
    13.         function add() {
    14.             //获得id为div1的元素
    15.             var div1Element = document.getElementById("div1") ;
    16.             div1Element.innerHTML += "
      "       ;
    17.         }
    18.         function del(who) {
    19.             //每次找到父类后将自身移除
    20.             who.parentNode.parentNode.removeChild(who.parentNode) ;
    21.         }
    22.     script>
    23. head>
    24. <body>
    25. <h1>多文件上传h1>
    26. <form action="${pageContext.request.contextPath}/UploadServlet" method="post" enctype="multipart/form-data">
    27.     文件描述:<input type="button" value="添加" onclick="add()">br>
    28.     <input type="submit" value="文件上传"><br/>
    29.     <div id="div1">
    30.  
    31.     div>
    32. form>
    33. body>
    34. html>

    3-防止上传重名文件覆盖问题

    防止不同浏览器上传重名的文件将原始的文件覆盖掉，故使用工具类生成唯一的文件名，工具类如下：

    1. import java.util.UUID;
    2.  
    3. /**
    4.  * 文件上传的工具类
    5.  */
    6. public class UploadUtils {
    7.     public static String getUuidFilename(String filename) {
    8.         //获得文件的扩展名
    9.         int index = filename.lastIndexOf(".");
    10.         String extension = filename.substring(index);
    11.         return UUID.randomUUID().toString().replace("-", "") + extension;
    12.     }
    13. }

    在servlet中使用该工具类对上传文件生成唯一的文件名，具体如下：

    1. import com.utils.UploadUtils;
    2. import org.apache.commons.fileupload.FileItem;
    3. import org.apache.commons.fileupload.FileUploadException;
    4. import org.apache.commons.fileupload.disk.DiskFileItemFactory;
    5. import org.apache.commons.fileupload.servlet.ServletFileUpload;
    6.  
    7. import javax.servlet.ServletException;
    8. import javax.servlet.http.HttpServlet;
    9. import javax.servlet.http.HttpServletRequest;
    10. import javax.servlet.http.HttpServletResponse;
    11. import java.io.*;
    12. import java.util.List;
    13.  
    14. public class UploadServlet extends HttpServlet {
    15.     @Override
    16.     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    17.         boolean flag = ServletFileUpload.isMultipartContent(req) ;
    18.         if(!flag){
    19.             //如果表单不是enctype="multipart/form-data"
    20.             req.setAttribute("msg","表单设置不正确");
    21.             req.getRequestDispatcher("/jsp/upload.jsp").forward(req,resp);
    22.         }
    23.         try {
    24.            //1.创建磁盘文件项工厂
    25.             DiskFileItemFactory diskFileItemFactory = new DiskFileItemFactory();
    26.             diskFileItemFactory.setSizeThreshold(3*1024*1024); //设置缓冲区的大小为3MB
    27.             //设置文件的临时路径
    28.             String temp = getServletContext().getRealPath("/temp") ;
    29.             diskFileItemFactory.setRepository(new File(temp));
    30.             //2.创建一个核心解析类
    31.             ServletFileUpload fileUpload = new ServletFileUpload(diskFileItemFactory) ;
    32.             //设置上传文件的大小为5MB
    33. //            fileUpload.setSizeMax(5*1024*1024);
    34.             //3.利用核心类解析Request，解析后会得到多个部分,存入list集合中
    35.             List list =  fileUpload.parseRequest(req) ;
    36.             //4.遍历文件项,判断文件项是普通项,还是文件上传项
    37.             for(FileItem fileItem : list){
    38.                 if(fileItem.isFormField()){
    39.                     //接收普通项的值
    40.                     String name = fileItem.getFieldName() ;
    41.                     String value = fileItem.getString("UTF-8") ;
    42.                     System.out.println(name + "   "+ value);
    43.                 }else{
    44.                     //文件上传项目
    45.                     //获得文件上传项的文件名及文件内容
    46.                     String filename = fileItem.getName() ;
    47.                     int index = filename.lastIndexOf("\\") ;
    48.                     if(index != -1){
    49.                         //老版本浏览器
    50.                         filename = filename.substring(index+1) ;
    51.                     }
    52.                     String filename1 = UploadUtils.getUuidFilename(filename) ;
    53.                     InputStream is = fileItem.getInputStream() ;
    54.                     //获得文件上传的磁盘绝对路径
    55.                     String realPath = getServletContext().getRealPath("/upload");
    56.                     //创建一个输出流,写入到真实的路径中
    57.                     OutputStream os = new FileOutputStream(realPath+"/"+filename1) ;
    58.                     //两个流实现对接
    59.                     int len = 0 ;
    60.                     byte [] bytes = new byte[1024] ;
    61.                     while((len=is.read(bytes)) != -1){
    62.                         os.write(bytes,0,len);
    63.                     }
    64.                     is.close();
    65.                     os.close();
    66.                 }
    67. //                fileItem.delete(); //删除临时文件
    68.             }
    69.         } catch (FileUploadException e) {
    70.             e.printStackTrace();
    71.         }
    72.     }
    73.  
    74.     @Override
    75.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    76.         doGet(req,resp);
    77.     }
    78. }

    4-文件下载之超链接方式

    文件下载方式1：超链接下载方式，下载服务器在download文件夹下的资源，代码如下：

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: nuist__NJUPT
    4.   Date: 2022-08-15
    5.   Time: 20:22
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <html>
    10. <head>
    11.     <title>Titletitle>
    12. head>
    13. <body>
    14. <h1>文件下载:超链接的方式h1>
    15. <h3><a href="${ pageContext.request.contextPath }/download/bootstrap-3.4.1-dist.zip">bootstrap.zipa>h3>
    16. <h3><a href="${ pageContext.request.contextPath }/download/a.docx">a.docxa>h3>
    17. body>
    18. html>

    5-文件下载之手动编写Servlet方式

    我们使用手动编写Servlet，将资源交给Servlet下载，首先在jsp页面将资源文件转给Servlet，代码如下：

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: nuist__NJUPT
    4.   Date: 2022-08-15
    5.   Time: 20:22
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@ page contentType="text/html;charset=UTF-8" language="java" %>
    9. <html>
    10. <head>
    11.     <title>Titletitle>
    12. head>
    13. <body>
    14.  
    15. <h1>文件下载:手动编程下载的方式h1>
    16. <h3><a href="${ pageContext.request.contextPath }/DownloadServlet?filename=bootstrap-3.4.1-dist.zip">bootstrap.zipa>h3>
    17. <h3><a href="${ pageContext.request.contextPath }/DownloadServlet?filename=a.docx">a.docxa>h3>
    18. body>
    19. html>

    然后编写用于处理文件下载的Servlet类，具体如下:

    1. import javax.servlet.ServletException;
    2. import javax.servlet.http.HttpServlet;
    3. import javax.servlet.http.HttpServletRequest;
    4. import javax.servlet.http.HttpServletResponse;
    5. import java.io.FileInputStream;
    6. import java.io.IOException;
    7. import java.io.InputStream;
    8. import java.io.OutputStream;
    9.  
    10. public class DownloadServlet extends HttpServlet {
    11.     @Override
    12.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    13.         //接收参数
    14.         String filename = request.getParameter("filename") ;
    15.         //下载，设置两个头和一个流
    16.         //设置Content-type
    17.         String type = request.getServletContext().getMimeType(filename) ;
    18.         response.setContentType(type);
    19.         //设置Content-Disposition
    20.         response.setHeader("Content-Disposition","attachment;filename="+filename);
    21.         //设置一个代表文件的输入流
    22.         String path = request.getServletContext().getRealPath("/download" ) ;
    23.         InputStream is = new FileInputStream(path+"/"+filename) ;
    24.         OutputStream os = response.getOutputStream() ;
    25.         //两个流的对接
    26.         int len = 0 ;
    27.         byte [] bytes = new byte[1024] ;
    28.         while((len=is.read(bytes)) != -1){
    29.             os.write(bytes,0,len);
    30.         }
    31.         is.close();
    32.         os.close();
    33.  
    34.     }
    35.  
    36.     @Override
    37.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    38.         doGet(req,resp);
    39.     }
    40. }

    最后需要在web.xml文件中配置Servlet，具体如下：

    2. <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    3.          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    4.          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
    5.          version="4.0">
    6.  
    7.     <servlet>
    8.         <servlet-name>DownloadServletservlet-name>
    9.         <servlet-class>com.controller.DownloadServletservlet-class>
    10.     servlet>
    11.     <servlet-mapping>
    12.         <servlet-name>DownloadServletservlet-name>
    13.         <url-pattern>/DownloadServleturl-pattern>
    14.     servlet-mapping>
    15. web-app>

    6-文件下载之防止浏览器不同下载乱码问题

    对于包含中文名称的文件，防止乱码，需要识别浏览器类型，并设置为UTF-8编码，具体的Servlet如下所示：

    1. import com.utils.DownloadUtils;
    2.  
    3. import javax.servlet.ServletException;
    4. import javax.servlet.http.HttpServlet;
    5. import javax.servlet.http.HttpServletRequest;
    6. import javax.servlet.http.HttpServletResponse;
    7. import java.io.*;
    8. import java.net.URLEncoder;
    9.  
    10. public class DownloadServlet extends HttpServlet {
    11.     @Override
    12.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    13.         //接收参数
    14.         String filename = new String(request.getParameter("filename").getBytes("ISO-8859-1"),"UTF-8");
    15.         //下载，设置两个头和一个流
    16.         //设置Content-type
    17.         String type = request.getServletContext().getMimeType(filename) ;
    18.         response.setContentType(type);
    19.         //设置一个代表文件的输入流
    20.         String path = request.getServletContext().getRealPath("/download" ) ;
    21.         File file = new File(path+"/"+filename);
    22.  
    23.         // 判断浏览器的类型:
    24.         String agent = request.getHeader("User-Agent");
    25.         if(agent.contains("Firefox")){
    26.             // 使用的是Firefox
    27.             filename = DownloadUtils.base64EncodeFileName(filename);
    28.         }else{
    29.             // IE或者其他的浏览器
    30.             filename = URLEncoder.encode(filename, "UTF-8");
    31.         }
    32.  
    33.         //设置Content-Disposition
    34.         response.setHeader("Content-Disposition","attachment;filename="+filename);
    35.  
    36.         InputStream is = new FileInputStream(file) ;
    37.         OutputStream os = response.getOutputStream() ;
    38.         //两个流的对接
    39.         int len = 0 ;
    40.         byte [] bytes = new byte[1024] ;
    41.         while((len=is.read(bytes)) != -1){
    42.             os.write(bytes,0,len);
    43.         }
    44.         is.close();
    45.         os.close();
    46.  
    47.     }
    48.  
    49.     @Override
    50.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    51.         doGet(req,resp);
    52.     }
    53. }

    当然这个servlet中对于火狐浏览器的编码问题使用了一个工具类，具体如下：

    1. import java.io.UnsupportedEncodingException;
    2.  
    3. import sun.misc.BASE64Encoder;
    4.  
    5. public class DownloadUtils {
    6.     public static String base64EncodeFileName(String fileName) {
    7.         BASE64Encoder base64Encoder = new BASE64Encoder();
    8.         try {
    9.             return "=?UTF-8?B?"
    10.                     + new String(base64Encoder.encode(fileName
    11.                     .getBytes("UTF-8"))) + "?=";
    12.         } catch (UnsupportedEncodingException e) {
    13.             e.printStackTrace();
    14.             throw new RuntimeException(e);
    15.         }
    16.     }
    17. }

    7-指定目录的文件下载案例

    定义一个jsp页面用于在浏览器显示目录中的所有文件。

    1. <%--
    2.   Created by IntelliJ IDEA.
    3.   User: nuist__NJUPT
    4.   Date: 2022-08-16
    5.   Time: 9:33
    6.   To change this template use File | Settings | File Templates.
    7. --%>
    8. <%@page import="java.io.File"%>
    9. <%@page import="java.util.*"%>
    10. <%@ page language="java" contentType="text/html; charset=UTF-8"
    11.          pageEncoding="UTF-8"%>
    12. html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    13. <html>
    14. <head>
    15.     <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    16.     <title>Insert title heretitle>
    17. head>
    18. <body>
    19. <h1>树形遍历h1>
    20. <%
    21.     // 1.创建一个队列：
    22.     Queue<File> queue = new LinkedList<File>();
    23.     // 2.先将跟节点入队：
    24.     File root = new File("E://resource");
    25.     queue.offer(root);
    26.     // 判断这个队列是否为空，不为空需要进行遍历:
    27.     while(!queue.isEmpty()){
    28.         // 将跟节点出队:
    29.         File file = queue.poll();
    30.         // 获得跟节点下的所有子节点:
    31.         File[] files = file.listFiles();
    32.         // 遍历所有子节点:
    33.         for(File f:files){
    34.             // 判断该节点是否为叶子节点:
    35.             if(f.isFile()){
    36. %>
    37. <h4><a href="${ pageContext.request.contextPath }/DownloadListServlet?filename=<%=f.getCanonicalPath()%>"><%= f.getName() %>a>h4>
    38. <%
    39.             }else{
    40.                 queue.offer(f);
    41.             }
    42.         }
    43.     }
    44. %>
    45. body>
    46. html>

    手动编写servlet处理文件下载问题，具体如下：
     

    1. import com.utils.DownloadUtils;
    2.  
    3. import javax.servlet.ServletException;
    4. import javax.servlet.http.HttpServlet;
    5. import javax.servlet.http.HttpServletRequest;
    6. import javax.servlet.http.HttpServletResponse;
    7. import java.io.*;
    8. import java.net.URLEncoder;
    9.  
    10. public class DownloadListServlet extends HttpServlet {
    11.     @Override
    12.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    13.         // 接收参数:
    14.         String path = request.getParameter("filename");
    15.         if(path != null){
    16.             path = new String(path.getBytes("ISO-8859-1"),"UTF-8");
    17.         }
    18.         File file = new File(path);
    19.         // 实现文件下载:设置两个头和一个流:
    20.         // 获得文件名
    21.         String filename = file.getName();
    22.         response.setContentType(getServletContext().getMimeType(filename));
    23.         // 设置另一个头：
    24.         String agent = request.getHeader("User-Agent");
    25.         if(agent.contains("Firefox")){
    26.             filename = DownloadUtils.base64EncodeFileName(filename);
    27.         }else{
    28.             filename = URLEncoder.encode(filename, "UTF-8");
    29.             filename = filename.replace("+", " ");
    30.         }
    31.         response.setHeader("Content-Disposition", "attachment;filename="+filename);
    32.         // 设置输入流:
    33.         InputStream is = new FileInputStream(file);
    34.         OutputStream os = response.getOutputStream();
    35.         int len = 0;
    36.         byte[] b = new byte[1024];
    37.         while((len = is.read(b))!=-1){
    38.             os.write(b, 0, len);
    39.         }
    40.         is.close();
    41.     }
    42.  
    43.     @Override
    44.     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    45.         doGet(req,resp);
    46.     }
    47. }

    在web.xml中配置servlet，具体如下：

    2. <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    3.          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    4.          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
    5.          version="4.0">
    6.  
    7.     <servlet>
    8.         <servlet-name>DownloadListServletservlet-name>
    9.         <servlet-class>com.controller.DownloadListServletservlet-class>
    10.     servlet>
    11.     <servlet-mapping>
    12.         <servlet-name>DownloadListServletservlet-name>
    13.         <url-pattern>/DownloadListServleturl-pattern>
    14.     servlet-mapping>
    15. web-app>
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  • 原文地址：https://blog.csdn.net/nuist_NJUPT/article/details/126350959