JavaWeb案例： 文件下载 基于tomcat8 默认编码为UTF-8

package cn.itcast.download;

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("/001")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取资源名
        String filename = request.getParameter("filename");
        //获取资源对应输入流
        FileInputStream fis = new FileInputStream(request.getServletContext().getRealPath("/download/" + filename));
        //告知类型
        response.setContentType(request.getServletContext().getMimeType(filename));
        //告知下载
        response.setHeader("content-disposition", "attachment;filename=" + filename);
        //获取响应输出流
        ServletOutputStream sos = response.getOutputStream();
        //写数据
        byte[] bys = new byte[1024 * 8];
        int len;
        while((len = fis.read(bys)) != -1){
            sos.write(bys, 0, len);
        }
        //释放资源
        fis.close();
    }

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

package cn.itcast.download;

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;
import java.net.URLEncoder;
import java.util.Base64;

@WebServlet("/download")
public class DownloadServlet2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //获取资源名
        String filename = request.getParameter("filename");
        //获取资源对应输入流
        FileInputStream fis = new FileInputStream(request.getServletContext().getRealPath("/download/" + filename));
        //告知类型
        response.setContentType(request.getServletContext().getMimeType(filename));
        //告知下载
        //处理响应头乱码，浏览器兼容性问题
        String agent = request.getHeader("user-agent");
        String fileNameEnc = null;
        if(agent.contains("MSIE")){
            fileNameEnc = URLEncoder.encode(filename,"UTF-8").replace("+", " ");
        }else if(agent.contains("Firefox")){
            fileNameEnc = "=?utf-8?B?"
                    + Base64.getEncoder().encodeToString(filename.getBytes("UTF-8"))
                    + "?=";
        }else{
            fileNameEnc = URLEncoder.encode(filename,"UTF-8");
        }
        response.setHeader("content-disposition", "attachment;filename=" + fileNameEnc);
        //获取响应输出流
        ServletOutputStream sos = response.getOutputStream();
        //写数据
        byte[] bys = new byte[1024 * 8];
        int len;
        while((len = fis.read(bys)) != -1){
            sos.write(bys, 0, len);
        }
        //释放资源
        fis.close();
    }

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