spring文件下载(一)

我们在前面讲了文件的上传，现在讲讲文件的下载。

文件下载主要就是设置我们Response的Headers中"Content-Disposition=attachment;filename=...。告诉我们浏览器要将数据保存到磁盘上,不在浏览器上直接解析。

前端

这里留一个坑，就是使用ajax请求前端下载文件是没有反应的，但是使用a标签就是没有问题

填坑

ajax回调已经把response的数据傻瓜式的以字符串的方式解析，ajax请求只是个“字符型”的请求，即请求的内容是以文本类型存放的。文件的下载是以二进制形式进行的，虽然可以读取到返回的response，但只是读取而已，console.log可以打印出读取的字符串，但是无法执行下载的。还可以使用post请求完成下载。
可以参考

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<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <script src="./js/jquery.min.js"></script>
    <script>
        let filetype = "";
        let url = "";
        let showPic = ()=> {
            let file = $("#file_input")[0].files[0];
            let formdata = new FormData();
            formdata.set("file", file)
            formdata.set("abv", "斯大林快回家")
            $.ajax({
                type: "post",
                processData: false,
                contentType: false,
                url: "http://localhost:8080/file_upload_ssm_war_exploded/upload_file",
                data: formdata,
                success(resp) {
                    $(".imgFile").attr("src",resp.url);
                    filetype = resp.filetype;
                    url = resp.url;
                    console.log(resp.message);
                    url = "http://localhost:8080/file_upload_ssm_war_exploded/download"+"?filetype="+filetype+"&photo="+resp.url;
                    $("#file_down").attr("href",url);
                }
            });

        };

    </script>
    <style type="text/css">
        .imgFile{
            width: 200px;
            height: 200px;
        }
    </style>
</head>
<body>
<h2>Hello World!</h2>

<form action="login">
    用户名：<input name="username"><br>
    密码：<input name="password"><br>
    头像：<br>
    <img class="imgFile" src="js:javascript(0)" ><br>
    <input id="file_input" type="file" name="file" onchange="showPic()">
    <a id="file_down" href="javascript:void(0)" >下载</a>

<%--    <input type="submit" /><br>--%>

</form>
</body>
</html>

后端

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package com.zgy.file.controller;

import com.sun.jersey.api.client.Client;
import com.sun.jersey.api.client.WebResource;
import com.zgy.file.service.FileService;
import org.apache.commons.io.IOUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.multipart.MultipartFile;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
import java.util.UUID;

@Controller
public class UploadController {
    public  String ServerUrl = "http://127.0.0.1:8090/upload/";
    @Autowired
    FileService service;

    @RequestMapping("/test")
    public ModelAndView test(){
        ModelAndView md = new ModelAndView();
        md.addObject("hh",service.testSSM());
        md.setViewName("forward:/showssm.jsp");
        return md;
    }


    @ResponseBody
    @RequestMapping("/upload_file")
    public Map<String,String> test(MultipartFile file,String abv,HttpServletRequest req) throws IOException {
        HashMap<String,String> map = new HashMap<>();
        String originalName = file.getOriginalFilename();
        String extendName = originalName.substring(originalName.lastIndexOf("."));
        String newName = UUID.randomUUID().toString().concat(extendName);

        Client client = Client.create();
        WebResource resource = client.resource(ServerUrl + newName);
        System.out.println(resource.put(String.class, file.getBytes()));
        map.put("message","success");
        map.put("url",ServerUrl + newName);
        map.put("filetype",file.getContentType());
        return map;
    }

    @RequestMapping("/download")
    public void download(String filetype,String photo,HttpServletResponse response) throws IOException {
        response.setContentType(filetype);
        String name = photo.substring(photo.lastIndexOf("/")+1);
        response.setHeader("Content-Disposition", "attachment;filename="+name);
        InputStream inputStream = new URL(photo).openStream();
        ServletOutputStream outputStream = response.getOutputStream();
        IOUtils.copy(inputStream,outputStream);
    }
}