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
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<%@ 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 >
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Servlet
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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();
}
}
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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:
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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);
}
});
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9. 在web页面中动态添加文件上传输入项
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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);
}
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上传jsp:
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<%@ 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 >
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上传servlet
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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);
}
}
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3. 下载功能
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//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);
}
}
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jsp显示
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<%@ 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 >
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下载处理servlet
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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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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服务器之家。