使用response实现文件的下载

在项目的资源目录下新建一个文件加，存放下载的文件

package com.guangtao.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
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;

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 1、获取要下载的文件
        String realPath = "D:\Java_File\javaweb-maven-servlet\response\src\main\resources\广涛.png";

        // 2、下载的文件命名是啥？   截取末尾的命名
        String filename = realPath.substring(realPath.lastIndexOf("\") + 1);  // 广涛.png

        // 3、加入支持浏览器下载的请求头
        // URLEncoder.encode(filename, "utf-8")  文件命名为中文则要设置编码格式
        resp.setHeader("Content-disposition", "attachment;filename=" + URLEncoder.encode(filename, "utf-8"));

        FileInputStream in = null;
        ServletOutputStream out = null;
        try {
            // 4、获取文件的流
            in = new FileInputStream(realPath);
            // 5、创建缓冲区
            int len = 0;
            byte[] buffer = new byte[1024];
            // 6、输出流
            out = resp.getOutputStream();
            // 7、将FileOutputStream 流写入到buffer缓冲区，使用OutputStream将缓冲区中的数据输出到客户端
            while ((len = in.read(buffer)) > 0) {
                out.write(buffer, 0, len);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {            // 关闭资源
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}