文件下载案例 January 27，2020

package web.download;

import javax.servlet.ServletContext;
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;
import java.io.FileInputStream;
import java.io.IOException;

@WebServlet("/downloadServlet")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.获取请求参数---文件名称
        String filename = request.getParameter("filename");
        //2.使用字节输入流加载文件进内存
        //2.1找到文件服务器路径
        ServletContext servletContext = this.getServletContext();
        String realPath = servletContext.getRealPath("/img/"+filename);
        //2.2用字节流关联
        FileInputStream fileInputStream = new FileInputStream(realPath);
        //3.设置response的响应头
        //3.1设置响应头类型：content-type

        String mimeType = servletContext.getMimeType(filename);
        response.setHeader("content-type",mimeType);
         /* 解决中文文件名问题
            //1.获取user-agent请求头、
            String agent = request.getHeader("user-agent");
            //2.使用工具类方法编码文件名即可
            filename = DownLoadUtils.getFileName(agent, filename);
           */
        //3.2设置响应头打开方式:content-disposition
        response.setHeader("content-disposition","attachment;filename="+filename);
        //4.将输入流的数据写出到输出流中
        ServletOutputStream sos = response.getOutputStream();
        byte [] buff = new byte[1024*8];
        int count = fileInputStream.read(buff);
        while (count!=-1){
            sos.write(buff,0,count);
            count = fileInputStream.read(buff);
        }
        fileInputStream.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

package web.utils;
/*
import sun.misc.BASE64Encoder;
import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;


public class DownLoadUtils {

    public static String getFileName(String agent, String filename) throws UnsupportedEncodingException {
        if (agent.contains("MSIE")) {
            // IE浏览器
            filename = URLEncoder.encode(filename, "utf-8");
            filename = filename.replace("+", " ");
        } else if (agent.contains("Firefox")) {
            // 火狐浏览器
            BASE64Encoder base64Encoder = new BASE64Encoder();
            filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
        } else {
            // 其它浏览器
            filename = URLEncoder.encode(filename, "utf-8");
        }
        return filename;
    }
}*/