Web-实现文件下载

超链接指向的资源如果能够被浏览器解析，则在浏览器中展示，如果不能解析，则弹出下载提示框。不满足需求
任何资源都必须弹出下载提示框
使用响应头设置资源的打开方式：
* content-disposition:attachment;filename=xxx

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <a href="/tomcatt/ds?filename=1.jpg">图片</a>
</body>
</html>

package servletcontext;

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.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.util.Enumeration;
import java.util.Map;
import java.util.Set;

@WebServlet("/ds")
public class DwonloadSerlvelet extends HttpServlet {
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
    
            //1.获取文件名称
            String filename=request.getParameter("filename");
            //2.使用字节输入流加载文件进入内存
            //2.1先找到文件服务器路径
            ServletContext sc=this.getServletContext();
            String rp=sc.getRealPath("/img/"+filename);
            //2.2用字节流关联
            FileInputStream fis=new FileInputStream(rp);

            //3.设置respose响应头
            //3.1设置响应头类型：content-type
            //获取文件的MIME类型
            String mimeTYpe=sc.getMimeType(filename);
            response.setHeader("content-type",mimeTYpe);
            //3.2设置响应头打开方式:content-disposition
            response.setHeader("content-disposition","attachment;filename"+filename);
            //4.将输入流的数据写出到输出流中
            ServletOutputStream sos= response.getOutputStream();
            byte[] buff=new byte[1024*8];
            int len=0;
            while((len=fis.read(buff))!=-1){
    
    
                sos.write(buff,0,len);
            }

    }

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

解决中文文件名乱码问题

package cn.itcast.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;
    }
}

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