转载

Servlet上传文件详细解析以及注意事项

准备阶段，下载需要的包: 在Servlet中进行文件上传需要用到外部的类库，apache提供了这些类库,　主要需要commons-fileupload.jar和commons-io.jar 下载的步骤如下：进入www.apache.org网站, ——>在Projects下找到commons，点击进入——>找到Components下的FileUpload,点击进入就可以找到下载页面如下：

可以看到这里有开发指南和下载地址，如果要详细学习，慢慢看这里的资源就可以了。 commons-io.jar包的下载地址:http://commons.apache.org/fileupload/dependencies.html 把两个jar包放到WEB-INF的lib目录下。 开发阶段: 上传页面:index.jsp

<%@ 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>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">
<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="upload" method="post" enctype="multipart/form-data">
文件别名:<input type="text" name="filename"><br>
选择文件:<input type="file" name="fileupload"><br>
<input type="submit" value="提交">
</form>
</body>
</html>

这里注意第24行，上传文件时要指定提交方法method="post",　信息类型为enctype="multipart/form-data" 上传功能servlet:FileUpload

package com.sunflower.servlet;
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
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.FileItemFactory;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
public class FileUpload extends HttpServlet {
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
fileControl(req, resp);
}
/**
* 上传文件的处理
*/
private void fileControl(HttpServletRequest req, HttpServletResponse resp) throws ServletException {
// 在解析请求之前先判断请求类型是否为文件上传类型
boolean isMultipart = ServletFileUpload.isMultipartContent(req);
// 文件上传处理工厂
FileItemFactory factory = new DiskFileItemFactory();
// 创建文件上传处理器
ServletFileUpload upload = new ServletFileUpload(factory);
// 开始解析请求信息
List items = null;
try {
items = upload.parseRequest(req);
}
catch (FileUploadException e) {
e.printStackTrace();
}
// 对所有请求信息进行判断
Iterator iter = items.iterator();
while (iter.hasNext()) {
FileItem item = (FileItem) iter.next();
// 信息为普通的格式
if (item.isFormField()) {
String fieldName = item.getFieldName();
String value = item.getString();
req.setAttribute(fieldName, value);
}
// 信息为文件格式
else {
String fileName = item.getName();
int index = fileName.lastIndexOf("//");
fileName = fileName.substring(index + 1);
req.setAttribute("realFileName", fileName);
// 将文件写入
// String path = req.getContextPath();
// String directory = "uploadFile";
// String basePath = req.getScheme() + "://" + req.getServerName() + ":" + req.getServerPort() + path + "/" + directory;
String basePath = req.getRealPath("/uploadFile");
File file = new File(basePath, fileName);
try {
item.write(file);
}
catch (Exception e) {
e.printStackTrace();
}
}
}
try {
req.getRequestDispatcher("/uploadsuccess.jsp").forward(req, resp);
}
catch (IOException e) {
e.printStackTrace();
}
}
}

这里要注意第66~68行，将文件上传到Web项目的"uploadFile"文件夹中，如果用这种方法得到的路径是"http://localhost:8080/upload/uploadFile", 而创建File类用的路径是绝对路径，这样就会出问题，所以这里要用的是得到真实路径的方法HttpServletRequest.getRealPath(). 以上是最简单的文件上传，如果要加入上传的限制可以在DiskFileItemFactory和ServletFileUpload中进行限制: 在34行后加入：