JavaWeb入门案例--文件下载使用ServletContent实现文件下载。文件下载需求：1. 页面显示超链接；2

使用ServletContent实现文件下载。

简单的下载页面 download.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <a href="/day_userLogin/img/1.jpg">图片1</a>
    <a href="/day_userLogin/img/2.jpg">图片2</a>
    <hr>
    <a href="/day_userLogin/downloadServlet?filename=/1.jpg">图片1</a>
    <a href="/day_userLogin/downloadServlet?filename=/2.jpg">图片2</a>
</body>
</html>

这是图片的目录

文件下载主要逻辑实现代码

package com.suntest.download;

import com.suntest.utils.DownLoadUtils;

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;

// ServletContent实现文件下载
@WebServlet("/downloadServlet")
public class DownloadServlet extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1、获取请求参数，文件名称
        String filename = req.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 fis = new FileInputStream(realPath);
        //3、设置response的响应头
        //3.1、设置响应头类型
        String mimeType = servletContext.getMimeType(filename);//获取文件的mime类型
        resp.setHeader("content-type",mimeType);
        //3.2、设置响应头打开方式：content-disposition
        resp.setHeader("content-disposition","attachment;filename="+filename);

        //解决中文文件名错误问题
        //1、获取user-agent请求头
        String agent = req.getHeader("user-agent");
        //2、使用工具类方法编码文件名即可
        filename = DownLoadUtils.getFileName(agent,filename);

        //4、将输入流的数据写入到输出流中
        ServletOutputStream sos = resp.getOutputStream();
        byte[] buff = new byte[1024 * 8];
        int len = 0;
        while ((len=fis.read(buff)) != -1){
            sos.write(buff,0,len);
        }
        fis.close();
    }

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

在解决中文乱码时，需要用到一个工具类，我在这也把工具类代码贴上。

DownloadUtils.java

package com.suntest.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;
    }
}