转载：原文连接https://blog.csdn.net/HaHa_Sir/article/details/81744629
一、前端 html 代码<center><h2> 基于servelt 3.0注解实现文件上传 </h2><h3>1、单个文件上传</h3><form action="${ctx }/uploadServlet" method="post" enctype="multipart/form-data">文件： <input type="file" name="uploadfile" ><br><br><br><button type="submit" >提交</button></form><hr><h3>2、 多个文件上传</h3><form action="${ctx }/uploadServlet" method="post" enctype="multipart/form-data">文件1： <input type="file" name="uploadfile" >文件2： <input type="file" name="uploadfile" >文件3： <input type="file" name="uploadfile" ><br><br><br><button type="submit" >提交</button></form>
</center>
二、uploadServlet 后端上传部分代码import java.io.File;
import java.io.IOException;
import java.util.Collection;
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;
/**
* 文件上传servlet
*/
@WebServlet("/uploadServlet")
// 该注解 将该Servlet 标记为一个文件上传的 servlet
@MultipartConfig
public class UploadServlet extends HttpServlet {private static final long serialVersionUID = 1L;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// 1、 获取文件的存储路径String realPath =         request.getServletContext().getRealPath(File.separator+"userfiles");File file = new File(realPath);if(!file.exists()){file.mkdirs();System.out.println("路径： "+realPath +" 创建成功!");}// 2、获取上传文件对象的集合Collection<Part> partList = request.getParts();if(partList.size() == 1){// 单个文件上传Part part = request.getPart("uploadfile");// 获取header 如： form-data; name="uploadfile"; filename="2018-08-11 开【华夏视讯网首发hxsxw.com】.mkv"String header = part.getHeader("content-disposition");// 获取文件名String fileName = header.split(";")[2].split("=")[1].replaceAll("\"", "");// 执行写入操作 --- 上传到指定的目录part.write(realPath+File.separator+fileName);}else{for (Part part : partList) {// 多个文件上传String header = part.getHeader("content-disposition");String fileName = getFileName(header);part.write(realPath+File.separator+fileName);}}request.setAttribute("message", "文件上传成功!");request.getRequestDispatcher("/WEB-INF/views/client/message.jsp").forward(request, response);}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}/*** 根据请求头解析出文件名* 请求头的格式：火狐和google浏览器下：form-data; name="file"; filename="snmp4j--api.zip"* IE浏览器下：form-data; name="file"; filename="E:\snmp4j--api.zip"* [@param](https://my.oschina.net/u/2303379) header 请求头* [@return](https://my.oschina.net/u/556800) 文件名* [@see](https://my.oschina.net/weimingwei) https://www.cnblogs.com/xdp-gacl/p/4224960.html* @date 2018年8月12日 22:57:27*/public String getFileName(String header) {/*** String[] tempArr1 = header.split(";");代码执行完之后，在不同的浏览器下，tempArr1数        组里面的内容稍有区别* 火狐或者google浏览器下：tempArr1={form-data,name="file",filename="snmp4j--api.zip"}* IE浏览器下：tempArr1={form-data,name="file",filename="E:\snmp4j--api.zip"}*/String[] tempArr1 = header.split(";");/***火狐或者google浏览器下：tempArr2={filename,"snmp4j--api.zip"}*IE浏览器下：tempArr2={filename,"E:\snmp4j--api.zip"}*/String[] tempArr2 = tempArr1[2].split("=");//获取文件名，兼容各种浏览器的写法String fileName = tempArr2[1].substring(tempArr2[1].lastIndexOf("\\")+1).replaceAll("\"", "");return fileName;}
}
三、DownLoadServlet 文件下载1、使用 response.getOutputStream(); 返回二进制数据流，实现文件下载2、 代码如下：import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLEncoder;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;/**
* 文件下载 servlet
*/
@WebServlet("/downloadServlet")
public class DownLoadServlet extends HttpServlet {private static final long serialVersionUID = 1L;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {// 1、文件存放路径String path="c:/";// 2、需要下载的文件名String fileName="default.png";File file = new File(path+fileName);response.reset();response.setCharacterEncoding("UTF-8");fileName = URLEncoder.encode(fileName, "UTF-8");response.setHeader("Content-Disposition", "attachment;fileName="+fileName);InputStream input = new FileInputStream(file);ServletOutputStream out = response.getOutputStream();byte[] buff =new byte[1024];int len ;while((len = input.read(buff)) != -1){out.write(buff, 0, len);out.flush();}input.close();out.close();}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}