commons fileupload实现文件上传的实例代码
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
<%@ 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
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