javaweb文件上传的九大问题
一、文件上传中要注意的9个问题
把保存上传文件的目录放到WEB-INF目录中。
2、中文乱码问题
2.1普通字段的中文请求参数
String value = FileItem.getString("UTF-8");
2.2上传的文件名是中文
解决办法：request.setCharacterEncoding("UTF-8");
3、重名文件被覆盖的问题
System.currentMillions()+"_"+a.txt(乐观)
UUID+"_"+a.txt:保证文件名唯一
4、分目录存储上传的文件
方式一：当前日期建立一个文件夹，当前上传的文件都放到此文件夹中。
例如：生成一个2014-10-6的文件夹
Date date = new Date();
DateFormat df = DateFormat.getDateInstance(DateFormat.MEDIUM);
String s = df.format(date);
String path = storePath+"\\"+s;
File file = new File(path);
if(!file.exists())
{
file.mkdirs();//创建多级目录，mkdir只创建一级目录
}
return path;//文件夹的地址
方式二：利用文件名的hash码打散目录来存储。
int hashCode = fileName.hashCode();
1001 1010 1101 0010 1101 1100 1101 1010
hashCode&0xf 0000 0000 0000 0000 0000 0000 0000 1111 &
---------------------------------------------
0000 0000 0000 0000 0000 0000 0000 1010 取hashCode的后4位
0000~1111：整数0~15共16个
1001 1010 1101 0010 1101 1100 1101 1010
(hashCode&0xf0) 0000 0000 0000 0000 0000 0000 1111 0000 &
--------------------------------------------
0000 0000 0000 0000 0000 0000 1101 0000 >>4
--------------------------------------------
0000 0000 0000 0000 0000 0000 0000 1101
0000~1111：整数0~15共16个
5、限制用户上传的文件类型
通过判断文件的扩展名来限制是不可取的。
通过判断其Mime类型才靠谱。FileItem.getContentType();
6.1单个文件大小限制。超出了大小友好提示
抓异常进行提示：org.apache.commons.fileupload.FileUploadBase.FileSizeLimitExceededException
6.2总文件大小限制。超出了大小友好提示
抓异常进行提示：org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException
commons-fileupload组件不会删除超出缓存的临时文件。
FileItem.delete()方法删除临时文件。但一定要在关闭流之后。
8、多个文件上传时，没有上传内容的问题
if(fileName==null||"".equals(fileName.trim())){
continue;
}
9、上传进度检测
给ServletFileUpload注册一个进度监听器即可，把上传进度传递给页面去显示
//pBytesRead：当前以读取到的字节数
//pContentLength：文件的长度
//pItems:第几项
public void update(long pBytesRead, long pContentLength,
int pItems) {
System.out.println("已读取："+pBytesRead+",文件大小："+pContentLength+",第几项："+pItems);
}
完整实例 :
表单：
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<base href="<%=basePath%>">
<title>My JSP '1.jsp' starting page</title>
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->
</head>
<body>
<form action="${pageContext.request.contextPath}/servlet/UploadServlet3" method="post" enctype="multipart/form-data">
用户名<input type="text" name="username"/> <br/>
<input type="file" name="f1"/><br/>
<input type="file" name="f2"/><br/>
<input type="submit" value="保存"/>
</form>
</body>
</html>
UploadServlet3
package com.mair.upload;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.text.DateFormat;
import java.util.Date;
import java.util.List;
import java.util.UUID;
import java.util.logging.SimpleFormatter;
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.FileUploadException;
import org.apache.commons.fileupload.ProgressListener;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
public class UploadServlet3 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//设置编码
request.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter pw = response.getWriter();
try {
//设置系统环境
DiskFileItemFactory factory = new DiskFileItemFactory();
//文件存储的路径
String storePath = getServletContext().getRealPath("/WEB-INF/files");
//判断传输方式 form enctype=multipart/form-data
boolean isMultipart = ServletFileUpload.isMultipartContent(request);
if(!isMultipart)
{
pw.write("传输方式有错误！");
return;
}
ServletFileUpload upload = new ServletFileUpload(factory);
upload.setFileSizeMax(4*1024*1024);//设置单个文件大小不能超过4M
upload.setSizeMax(4*1024*1024);//设置总文件上传大小不能超过6M
//监听上传进度
upload.setProgressListener(new ProgressListener() {
//pBytesRead：当前以读取到的字节数
//pContentLength：文件的长度
//pItems:第几项
public void update(long pBytesRead, long pContentLength,
int pItems) {
System.out.println("已读去文件字节 :"+pBytesRead+" 文件总长度："+pContentLength+" 第"+pItems+"项");
}
});
//解析
List<FileItem> items = upload.parseRequest(request);
for(FileItem item: items)
{
if(item.isFormField())//普通字段，表单提交过来的
{
String name = item.getFieldName();
String value = item.getString("UTF-8");
System.out.println(name+"=="+value);
}else
{
// String mimeType = item.getContentType(); 获取上传文件类型
// if(mimeType.startsWith("image")){
InputStream in =item.getInputStream();
String fileName = item.getName();
if(fileName==null || "".equals(fileName.trim()))
{
continue;
}
fileName = fileName.substring(fileName.lastIndexOf("\\")+1);
fileName = UUID.randomUUID()+"_"+fileName;
//按日期来建文件夹
String newStorePath = makeStorePath(storePath);
String storeFile = newStorePath+"\\"+fileName;
OutputStream out = new FileOutputStream(storeFile);
byte[] b = new byte[1024];
int len = -1;
while((len = in.read(b))!=-1)
{
out.write(b,0,len);
}
in.close();
out.close();
item.delete();//删除临时文件
}
}
// }
}catch(org.apache.commons.fileupload.FileUploadBase.FileSizeLimitExceededException e){
//单个文件超出异常
pw.write("单个文件不能超过4M");
}catch(org.apache.commons.fileupload.FileUploadBase.SizeLimitExceededException e){
//总文件超出异常
pw.write("总文件不能超过6M");
}catch (FileUploadException e) {
e.printStackTrace();
}
}
//用日期生成的目录，如果想用hashcode，后面
private String makeStorePath(String storePath) {
Date date = new Date();
DateFormat df = DateFormat.getDateInstance(DateFormat.MEDIUM);
String s = df.format(date);
String path = storePath+"\\"+s;
File file = new File(path);
if(!file.exists())
{
file.mkdirs();//创建多级目录，mkdir只创建一级目录
}
return path;
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
用hashcode生成目录：只需要改写一下makeStorePath(String storePath, String fileName)函数
private String makeStorePath(String storePath, String fileName) {
int hashCode = fileName.hashCode();
int dir1 = hashCode & 0xf;// 0000~1111：整数0~15共16个
int dir2 = (hashCode & 0xf0) >> 4;// 0000~1111：整数0~15共16个
String path = storePath + "\\" + dir1 + "\\" + dir2; // WEB-INF/files/1/12
File file = new File(path);
if (!file.exists())
file.mkdirs();
return path;
}