javaweb 中如何使用Response下载文件（源代码）

1.项目结构

2.FileServlet.java

package com.gaokai.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;

public class FileServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
     //     1.要获取下载文件的路径
        String realPath ="E:\\ideaWorkspace\\javaweb-01-servlet\\response\\src\\main\\resources\\1.png";
        System.out.println("下载文件的路径："+realPath);
     //     2.下载的文件名是啥？
        String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
        //     3.设置想办法让浏览器能够支持下载我们需要的东西
        resp.setHeader("Content-Disposition","attachment;filename="+fileName);
     //     4.获取下载文件的输入流
        FileInputStream in = new FileInputStream(realPath);
     //     5.创建缓冲区
        int len=0;
        byte[] buffer = new byte[1024];
        //     6.获取OutPutStream对象
        ServletOutputStream 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);
        }
        in.close();
        out.close();
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    }
}

3.web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app>
  xmlns="http://xmlns.jcp.org/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemalocation="http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
  version="4.0"
  metadata-complete="true">
  <servlet>
    <servlet-name>filedown</servlet-name>
    <servlet-class>com.gaokai.servlet.FileServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>filedown</servlet-name>
    <url-pattern>/down</url-pattern>
  </servlet-mapping>
</web-app>

4.浏览器后添加：down