原生Servlet文件上传和下载Servlet多个文件上传

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);
    }

}