一、文件上传的原理分析
1、文件上传的必要前提
a、表单的method必须是post
b、表单的enctype属性必须是multipart/form-data类型的。
enctype默认值：application/x-www-form-urlencoded
作用：告知服务器，请求正文的mime类型
application/x-www-form-urlencoded ： username=abc&password=123
servletrequest.getparameter(string name);该方法是专门读取该类型的方法
multipart/form-data:
2、借助commons-fileupload组件实现文件的上传
a、拷贝jar包：commons-fileupload.jar commons-io.jar
b、实现原理
3、乱码问题
a、普通字段的乱码
fileitem.getstring(string charset);编码要和客户端一致
b、上传的中文文件名乱码
request.setcharacterencoding("utf-8");编码要和客户端一致
4、具体实现
前台upload.jsp代码如下
我要评论
<%@ page language="java" import="java.util.*" pageencoding="utf-8"%>
<!doctype html public "-//w3c//dtd html 4.01 transitional//en">
<html>
<head>
<title>文件上传</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form action="${pagecontext.request.contextpath}/servlet/uploadservlet3" method="post" enctype="multipart/form-data">
name:<input name="name"/><br/>
file1:<input type="file" name="f1"/><br/>
file2:<input type="file" name="f2"/><br/>
<input type="submit" value="上传">
</form>
</body>
</html>
后台servlet代码
package com.itheima.servlet;
import java.io.file;
import java.io.ioexception;
import java.io.printwriter;
import java.io.unsupportedencodingexception;
import java.util.list;
import java.util.uuid;
import javax.servlet.servletexception;
import javax.servlet.http.httpservlet;
import javax.servlet.http.httpservletrequest;
import javax.servlet.http.httpservletresponse;
import org.apache.commons.fileupload.fileitem;
import org.apache.commons.fileupload.fileuploadbase;
import org.apache.commons.fileupload.fileuploadexception;
import org.apache.commons.fileupload.disk.diskfileitemfactory;
import org.apache.commons.fileupload.servlet.servletfileupload;
import org.apache.commons.io.filenameutils;
//详解
public class uploadservlet3 extends httpservlet {
public void doget(httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
request.setcharacterencoding("utf-8");
response.setcontenttype("text/html;charset=utf-8");
printwriter out = response.getwriter();
system.out.print(request.getremoteaddr());
boolean ismultipart = servletfileupload.ismultipartcontent(request);
if(!ismultipart){
throw new runtimeexception("请检查您的表单的enctype属性，确定是multipart/form-data");
}
diskfileitemfactory dfif = new diskfileitemfactory();
servletfileupload parser = new servletfileupload(dfif);
// parser.setfilesizemax(3*1024*1024);//设置单个文件上传的大小
// parser.setsizemax(6*1024*1024);//多文件上传时总大小限制
list<fileitem> items = null;
try {
items = parser.parserequest(request);
}catch(fileuploadbase.filesizelimitexceededexception e) {
out.write("上传文件超出了3m");
return;
}catch(fileuploadbase.sizelimitexceededexception e){
out.write("总文件超出了6m");
return;
}catch (fileuploadexception e) {
e.printstacktrace();
throw new runtimeexception("解析上传内容失败，请重新试一下");
}
//处理请求内容
if(items!=null){
for(fileitem item:items){
if(item.isformfield()){
processformfield(item);
}else{
processuploadfield(item);
}
}
}
out.write("上传成功！");
}
private void processuploadfield(fileitem item) {
try {
string filename = item.getname();
//用户没有选择上传文件时
if(filename!=null&&!filename.equals("")){
filename = uuid.randomuuid().tostring()+"_"+filenameutils.getname(filename);
//扩展名
string extension = filenameutils.getextension(filename);
//mime类型
string contenttype = item.getcontenttype();
if(contenttype.startswith("image/")){
//分目录存储：日期解决
// date now = new date();
// dateformat df = new simpledateformat("yyyy-mm-dd");
//
// string childdirectory = df.format(now);
//按照文件名的hashcode计算存储目录
string childdirectory = makechilddirectory(getservletcontext().getrealpath("/web-inf/files/"),filename);
string storedirectorypath = getservletcontext().getrealpath("/web-inf/files/"+childdirectory);
file storedirectory = new file(storedirectorypath);
if(!storedirectory.exists()){
storedirectory.mkdirs();
}
system.out.println(filename);
item.write(new file(storedirectorypath+file.separator+filename));//删除临时文件
}
}
} catch (exception e) {
throw new runtimeexception("上传失败,请重试");
}
}
//计算存放的子目录
private string makechilddirectory(string realpath, string filename) {
int hashcode = filename.hashcode();
int dir1 = hashcode&0xf;// 取1~4位
int dir2 = (hashcode&0xf0)>>4;//取5~8位
string directory = ""+dir1+file.separator+dir2;
file file = new file(realpath,directory);
if(!file.exists())
file.mkdirs();
return directory;
}
private void processformfield(fileitem item) {
string fieldname = item.getfieldname();//字段名
string fieldvalue;
try {
fieldvalue = item.getstring("utf-8");
} catch (unsupportedencodingexception e) {
throw new runtimeexception("不支持utf-8编码");
}
system.out.println(fieldname+"="+fieldvalue);
}
public void dopost(httpservletrequest request, httpservletresponse response)
throws servletexception, ioexception {
doget(request, response);
}
}
5、关于临时文件问题
a、diskfileitemfactory
public void setrepository(file repository)：设置临时文件的存放目录
public void setsizethreshold(int sizethreshold)：设置缓存的大小
b、
文件上传时，自己用io流处理，一定要在流关闭后删除临时文件。fileitem.delete()
建议使用：fileitem.writer(file f).会自动删除临时文件。
6、限制文件的大小
a、
servletfileupload.setfilesizemax(3*1024*1024);//设置单个文件上传的大小
b、
servletfileupload.setsizemax(6*1024*1024);//多文件上传时总大小限制
以上所述是小编给大家介绍的commons fileupload实现文件上传的实例代码，希望对大家有所帮助
如对本文有疑问， 点击进行留言回复！！
浅谈Java如何实现一个基于LRU时间复杂度为O(1)的缓存
JDK1.6“新“特性Instrumentation之JavaAgent(推荐)
before社区电量是什么意思 Before社区电量获得方法
网友评论