假设实现文件上传难道非要借助第三方jar包（最经常使用的莫过于apache的commons-fileupload工具包）来实现吗？答案是否定的。以下通过样例演示在不借助第三方jar包的前提下怎样实现文件的上传：
1、servlet文件代码：
package com.ghj.packageofservlet;
import java.io.IOException;
import java.util.UUID;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import org.apache.commons.io.FilenameUtils;
import org.apache.commons.lang.StringUtils;
/**
* 用于接收文件上传请求
*
* @author GaoHuanjie
*/
@WebServlet(urlPatterns = "/UploadServlet")
@MultipartConfig(location = "C:/upload/", maxFileSize = 1024 * 1024 * 10)
public class UploadServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
@Override
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
request.setCharacterEncoding("UTF-8");
try{
Part part = request.getPart("photo");
if(part.getSize() == 0l){
request.setAttribute("result", "请选择要上传的文件！！。");
}else{
String fileSuffix = FilenameUtils.getExtension(StringUtils.substringBetween(part.getHeader("content-disposition"), "filename="", """));
part.write(UUID.randomUUID().toString() + "." + fileSuffix);
request.setAttribute("result", "文件成功上传。！！");
}
}catch (Exception e) {
if(e.getMessage().contains("its maximum permitted size ")){
e.printStackTrace();
request.setAttribute("result", "上传文件过大，请又一次选择！！！");
}else{
e.printStackTrace();
request.setAttribute("result", "系统出现故障，请联系管理员！。。");
}
}
request.getRequestDispatcher("result.jsp").forward(request, response);
}
}
说明：上面servlet依赖于commons-io-2.4.jar和commons-lang-2.5.jar两个jar包。主要实现获取上传文件类型的功能。
2、web.xml文件代码：
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
3、站点首页文件代码：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <% String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+request.getContextPath()+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>借助Servlet3.0实现文件上传</title> </head> <body> <form action="<%=basePath%>UploadServlet" method="post" enctype="multipart/form-data"> 文件上传：<input type="file" id="photo" name="photo"/> <input type="submit" value="開始上传" /> </form> </body> </html>
4、上传文件结果文件代码：
<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>文件上传结果</title>
</head>
<body>
<center style="margin-top: 20%">
<font style="font-size: 36pt;font-weight: bold;color: red;"><%=request.getAttribute("result") %></font>
</center>
</body>
</html> 【0分资源下载——servlet3.0文件上传 01.zip】
【0分资源下载——servlet3.0文件上传 02.zip】
说明：上面两个样例的代码基本同样，唯一的差别是：第一个样例是把文件上传到了C盘upload目录内，而第二个样例是把文件上传到了公布项目的server上。