当使用enctype后 --- multipart/form-data
上传文件请求体 采用MIME消息格式 格式如下：
分析原理之后 需要使用开源技术来解决
1、JSP Smart-upload (产生于JSP盛行时代 Model1)
parseRequest ---- FileItem的List
什么是FileItem ----- MIME BodyPart
2、遍历List，寻找哪个是上传文件的FileItem
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
</head>
<body>
<h1>文件上传 form 表单</h1>
<form action="upload4" method="post" enctype="multipart/form-data">
用户名<input type="text" name="username" /><br/>
上传文件<input type="file" name="upload"/> <!-- 以post提交 数据在请求体中 -->
<input type="submit" />
</form>
</body>
</html>package cn.servlet;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
public class UploadServlet2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// 使用file upload 技术 进行文件上传
// 创建文件项工厂
DiskFileItemFactory factory = new DiskFileItemFactory(); // 目的：存放
// 创建ServletFileUpload
ServletFileUpload servletFileUpload = new ServletFileUpload(factory); // 解析器
// 解析
try {
// 获得文件项列表 -- 每一个文件项相当于 一个上传表单组件
List<FileItem> fileItems = servletFileUpload.parseRequest(request);
System.out.println(fileItems.size());
// 查找哪个是上传文件项
for (FileItem fileItem : fileItems) {
// 判断fileItem是上传文件
if (!fileItem.isFormField()) {
// 上传文件
InputStream in = fileItem.getInputStream();
String fileName = fileItem.getName();
int index = fileName.lastIndexOf("\\");
if (index != -1) {
// 截取文件名
fileName = fileName.substring(index + 1);
}
FileOutputStream out = new FileOutputStream("c:\\"
+ fileName);
int temp;
while ((temp = in.read()) != -1) {
out.write(temp);
}
in.close();
out.close();
}
}
} catch (FileUploadException e) {
e.printStackTrace();
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}