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java中借助commons-fileupload实现文件上传

  • 时间:2016-10-24
  • 发布:昆明Java培训
  • 来源:达内新闻

昆明Java培训机构的老师今天讲在java中借助commons-fileupload实现文件上传

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 ame);该方法是专门读取该类型的方法

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" ame="f1"/><br/>

file2:<input type="file" ame="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

了解详情请登陆昆明达内Java培训官网(km.Java.tedu.cn)!

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