JavaWeb文件上传下载功能示例解析

  • Z时代
  • 2024-01-10
  • 分类：IT

在Web应用系统开发中，文件上传和下载功能是非常常用的功能，今天来讲一下JavaWeb中的文件上传和下载功能的实现。

1. 上传简单示例

Jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>文件上传下载</title>
</head>
<body>
<form action="${pageContext.request.contextPath}/UploadServlet" enctype="multipart/form-data" method="post">
 上传用户：<input type="text" name="username" /> <br />
 上传文件1：<input type="file" name="file1" /> <br />
 上传文件2：<input type="file" name="file2" /> <br />
 <input type="submit" value="上传 "/>
</form> 
<br />
${requestScope.message}
</body>
</html>

Servlet

public void doGet(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 try{
 //1.得到解析器工厂
 DiskFileItemFactory factory = new DiskFileItemFactory();
 //2.得到解析器
 ServletFileUpload upload = new ServletFileUpload(factory);
 //3.判断上传表单的类型
 if(!upload.isMultipartContent(request)){
  //上传表单为普通表单，则按照传统方式获取数据即可
  return;
 }
 //为上传表单，则调用解析器解析上传数据
 List<FileItem> list = upload.parseRequest(request); //FileItem
 //遍历list，得到用于封装第一个上传输入项数据fileItem对象
 for(FileItem item : list){
  if(item.isFormField()){
  //得到的是普通输入项
  String name = item.getFieldName(); //得到输入项的名称
  String value = item.getString();
  System.out.println(name + "=" + value);
  }else{
  //得到上传输入项
  String filename = item.getName(); //得到上传文件名 C:\Documents and Settings\ThinkPad\桌面\1.txt
  filename = filename.substring(filename.lastIndexOf("\\")+1);
  InputStream in = item.getInputStream();  //得到上传数据
  int len = 0;
  byte buffer[]= new byte[1024];
  //用于保存上传文件的目录应该禁止外界直接访问
  String savepath = this.getServletContext().getRealPath("/WEB-INF/upload");
  System.out.println(savepath);
  FileOutputStream out = new FileOutputStream(savepath + "/" + filename); //向upload目录中写入文件
  while((len=in.read(buffer))>0){
  out.write(buffer, 0, len);
  }
  in.close();
  out.close();
  request.setAttribute("message", "上传成功");
  }
 }
 }catch (Exception e) {
  request.setAttribute("message", "上传失败");
  e.printStackTrace();
 }
 }

2. 修改后的上传功能：

注意事项：

1、上传文件名的中文乱码和上传数据的中文乱码

 upload.setHeaderEncoding("UTF-8");  //解决上传文件名的中文乱码

 //表单为文件上传，设置request编码无效,只能手工转换

 1.1 value = new String(value.getBytes("iso8859-1"),"UTF-8");

 1.2 String value = item.getString("UTF-8"); 

2.为保证服务器安全，上传文件应该放在外界无法直接访问的目录

3、为防止文件覆盖的现象发生，要为上传文件产生一个唯一的文件名

4、为防止一个目录下面出现太多文件，要使用hash算法打散存储

5.要限制上传文件的最大值，可以通过：ServletFileUpload.setFileSizeMax(1024)方法实现，并通过捕获：

 FileUploadBase.FileSizeLimitExceededException异常以给用户友好提示

6.想确保临时文件被删除，一定要在处理完上传文件后，调用item.delete方法

7.要限止上传文件的类型：在收到上传文件名时，判断后缀名是否合法

8、监听文件上传进度：

 ServletFileUpload upload = new ServletFileUpload(factory);
  upload.setProgressListener(new ProgressListener(){
  public void update(long pBytesRead, long pContentLength, int arg2) {
   System.out.println("文件大小为：" + pContentLength + ",当前已处理：" + pBytesRead);
  }
  });

9. 在web页面中动态添加文件上传输入项

 function addinput(){
   var div = document.getElementById("file");
   var input = document.createElement("input");
   input.type="file";
   input.name="filename";
   var del = document.createElement("input");
   del.type="button";
   del.value="删除";
   del.onclick = function d(){
    this.parentNode.parentNode.removeChild(this.parentNode);
   }
   var innerdiv = document.createElement("div");
   innerdiv.appendChild(input);
   innerdiv.appendChild(del);
   div.appendChild(innerdiv);
   }

上传jsp:

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
  <title>My JSP 'upload2.jsp' starting page</title>
  <script type="text/javascript">
   function addinput(){
   var div = document.getElementById("file");
   var input = document.createElement("input");
   input.type="file";
   input.name="filename";
   var del = document.createElement("input");
   del.type="button";
   del.value="删除";
   del.onclick = function d(){
    this.parentNode.parentNode.removeChild(this.parentNode);
   }
   var innerdiv = document.createElement("div");
   innerdiv.appendChild(input);
   innerdiv.appendChild(del);
   div.appendChild(innerdiv);
   }
  </script>
 </head>
 <body>
  <form action="" enctype="mutlipart/form-data"></form>
  <table>
   <tr>
   <td>上传用户：</td>
   <td><input type="text" name="username"></td>
   </tr>
 <tr>   
   <td>上传文件：</td>
   <td>
    <input type="button" value="添加上传文件" onclick="addinput()">
    </td>
   </tr>
   <tr>
    <td></td>
   <td>
    <div id="file">
    </div>
    </td>
   </tr>
  </table>
 </body>
</html>

上传servlet

public class UploadServlet1 extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 //request.getParameter("username"); //****错误
 request.setCharacterEncoding("UTF-8"); //表单为文件上传，设置request编码无效
 //得到上传文件的保存目录
 String savePath = this.getServletContext().getRealPath("/WEB-INF/upload");
 try{
  DiskFileItemFactory factory = new DiskFileItemFactory();
  factory.setRepository(new File(this.getServletContext().getRealPath("/WEB-INF/temp")));
  ServletFileUpload upload = new ServletFileUpload(factory);
  /*upload.setProgressListener(new ProgressListener(){
  public void update(long pBytesRead, long pContentLength, int arg2) {
   System.out.println("文件大小为：" + pContentLength + ",当前已处理：" + pBytesRead);
  }
  });*/
  upload.setHeaderEncoding("UTF-8"); //解决上传文件名的中文乱码
  if(!upload.isMultipartContent(request)){
  //按照传统方式获取数据
  return;
  }
  /*upload.setFileSizeMax(1024);
  upload.setSizeMax(1024*10);*/
  List<FileItem> list = upload.parseRequest(request);
  for(FileItem item : list){
  if(item.isFormField()){
   //fileitem中封装的是普通输入项的数据
   String name = item.getFieldName();
   String value = item.getString("UTF-8");
   //value = new String(value.getBytes("iso8859-1"),"UTF-8");
   System.out.println(name + "=" + value);
  }else{
   //fileitem中封装的是上传文件
   String filename = item.getName(); //不同的浏览器提交的文件是不一样 c:\a\b\1.txt  1.txt
   System.out.println(filename);
   if(filename==null || filename.trim().equals("")){
   continue;
   }
   filename = filename.substring(filename.lastIndexOf("\\")+1);
   InputStream in = item.getInputStream();
   String saveFilename = makeFileName(filename); //得到文件保存的名称
   String realSavePath = makePath(saveFilename, savePath); //得到文件的保存目录
   FileOutputStream out = new FileOutputStream(realSavePath + "\\" + saveFilename);
   byte buffer[] = new byte[1024];
   int len = 0;
   while((len=in.read(buffer))>0){
   out.write(buffer, 0, len);
   }
   in.close();
   out.close();
   item.delete(); //删除临时文件
  }
  }
 }catch (FileUploadBase.FileSizeLimitExceededException e) {
  e.printStackTrace();
  request.setAttribute("message", "文件超出最大值！！！");
  request.getRequestDispatcher("/message.jsp").forward(request, response);
  return;
 }
 catch (Exception e) {
  e.printStackTrace();
 }
 }
 public String makeFileName(String filename){ //2.jpg
 return UUID.randomUUID().toString() + "_" + filename;
 }
 public String makePath(String filename,String savePath){
 int hashcode = filename.hashCode();
 int dir1 = hashcode&0xf; //0--15
 int dir2 = (hashcode&0xf0)>>4; //0-15
 String dir = savePath + "\\" + dir1 + "\\" + dir2; //upload\2\3 upload\3\5
 File file = new File(dir);
 if(!file.exists()){
  file.mkdirs();
 }
 return dir;
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 doGet(request, response);
 }
}

3. 下载功能

//列出网站所有下载文件
public class ListFileServlet extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 String filepath = this.getServletContext().getRealPath("/WEB-INF/upload");
 Map map = new HashMap();
 listfile(new File(filepath),map);
 request.setAttribute("map", map);
 request.getRequestDispatcher("/listfile.jsp").forward(request, response);
 }
 public void listfile(File file,Map map){
 if(!file.isFile()){
  File files[] = file.listFiles();
  for(File f : files){
  listfile(f,map);
  }
 }else{
  String realname = file.getName().substring(file.getName().indexOf("_")+1); //9349249849-88343-8344_阿_凡_达.avi
  map.put(file.getName(), realname);
 }
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 doGet(request, response);
 }
}

jsp显示

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
 <head>
  <title>My JSP 'listfile.jsp' starting page</title>
 </head>
 <body>
  <c:forEach var="me" items="${map}">
   <c:url value="/servlet/DownLoadServlet" var="downurl">
   <c:param name="filename" value="${me.key}"></c:param>
   </c:url>
   ${me.value } <a href="${downurl}">下载</a> <br/>
  </c:forEach>
 </body>
</html>

下载处理servlet

public class DownLoadServlet extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 String filename = request.getParameter("filename"); //23239283-92489-阿凡达.avi
 filename = new String(filename.getBytes("iso8859-1"),"UTF-8");
 String path = makePath(filename,this.getServletContext().getRealPath("/WEB-INF/upload"));
 File file = new File(path + "\\" + filename);
 if(!file.exists()){
  request.setAttribute("message", "您要下载的资源已被删除！！");
  request.getRequestDispatcher("/message.jsp").forward(request, response);
  return;
 }
 String realname = filename.substring(filename.indexOf("_")+1);
 response.setHeader("content-disposition", "attachment;filename=" + URLEncoder.encode(realname, "UTF-8"));
 FileInputStream in = new FileInputStream(path + "\\" + filename);
 OutputStream out = response.getOutputStream();
 byte buffer[] = new byte[1024];
 int len = 0;
 while((len=in.read(buffer))>0){
  out.write(buffer, 0, len);
 }
 in.close();
 out.close();
 }
 public String makePath(String filename,String savePath){
 int hashcode = filename.hashCode();
 int dir1 = hashcode&0xf; //0--15
 int dir2 = (hashcode&0xf0)>>4; //0-15
 String dir = savePath + "\\" + dir1 + "\\" + dir2; //upload\2\3 upload\3\5
 File file = new File(dir);
 if(!file.exists()){
  file.mkdirs();
 }
 return dir;
 }
 public void doPost(HttpServletRequest request, HttpServletResponse response)
  throws ServletException, IOException {
 doGet(request, response);
 }
}

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