javaweb下载文件

1. 要获取下载文件的路径
2. 下载的文件名是啥？
3. 设置想办法让浏览器能够支持下载我们需要的东西
4. 获取下载文件的输入流
5. 创建缓冲区
6. 获取OutputStream对象
7. 将FileOutputStream流写入到bufer缓冲区
8. 使用OutputStream将缓冲区中的数据输出到客户端！

package com.beijing.servlet.File;

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.*;
import java.net.URLEncoder;

public class FileDownloadServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.download(req, resp);
    }

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

    private void download(HttpServletRequest req, HttpServletResponse resp) throws IOException {
//        1. 要获取下载文件的路径
        String relPath = "C:\\Users\\史凯翔\\Pictures\\Camera Roll\\afe7fab630484fefa566d24294c18408.jpg";

//        2. 下载的文件名是啥？
        String fileName = relPath.substring(relPath.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,中文文件名URLEncoder.encode编码，否则有可能乱码
        resp.setHeader("ContentDisposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));

//        4. 获取下载文件的输入流
        FileInputStream fis = new FileInputStream(relPath);

//        5. 创建缓冲区
        BufferedInputStream bis = new BufferedInputStream(fis);

        //一次读取一个字节数组
        int len = 0;
        byte[] bytes = new byte[1024];

//        6. 获取OutputStream对象
        ServletOutputStream os = resp.getOutputStream();
        BufferedOutputStream bos = new BufferedOutputStream(os);

//        7. 将FileOutputStream流写入到bufer缓冲区,使用OutputStream将缓冲区中的数据输出到客户端！
        while ((len = bis.read(bytes)) > 0) {
            bos.write(bytes,0,len);
        }
//        8.关闭流
        bis.close();
        fis.close();
        bos.close();
        os.close();
    }
}