JavaWeb文件上传下载功能示例解析

前端技术 2023/09/03 Java

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);
 }

}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持phpstudy。

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