欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识！
您现在的位置是： 首页  >  IT编程

JavaWeb文件上传下载功能示例解析

程序员文章站 2024-03-12 18:26:56
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 <...

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

JavaWeb文件上传下载功能示例解析

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。

上一篇： 多用多学之Java中的Set,List,Map详解

下一篇： Eclipse安装配置方法图文教程

推荐阅读