Spring Mvc下实现以文件流方式下载文件的方法示例

项目中需要对一个点击事件进行下载操作，同时通过点击事件，已经可以从jsp页面获取到需要访问的URL和下载的文件名（数据库获取，jsp页面显示）。点击事件JS如下：

function downloadFile(filePath,fileName){

 fileName = fileName.substr(0,fileName.lastIndexOf("."));
 $.ajax({
   async : false,
   cache:false,
   type: 'get',
   dataType : "json",
   url: RootPath() + "/checkDownload",//请求的action路径
   data:{url:filePath},
   error: function () {//请求失败处理函数
     alert("下载失败");
   },
   success:function(json) { //请求成功后处理函数。
   var code = json.code;
   if(code) {
    window.location.href = RootPath()+"/todownload?url="+filePath+"&name="+fileName;
   }else {
    layer.alert(fileName+' 文件不存在');
   }
   }
 });

}

该ajax调用后台（checkDownload）方法，首先判断从该url能否获得指定下载的文件，如果获取不到，方法返回参数code=0，页面弹出“...文件不存在”。

 @RequestMapping("/checkDownload")
 @ResponseBody
 public Result checkDownload(String url,HttpServletResponse response) {
 Result result = Result.createSuccessResult();
 HttpURLConnection conn = null;
 try {
  URL path = new URL(url);
  conn = (HttpURLConnection) path.openConnection();
  conn.setRequestMethod("GET");
  conn.setConnectTimeout(5 * 1000);
  conn.getInputStream();// 通过输入流获取数据
 } catch (IOException ex) {
  result.setCode(0);
  ex.printStackTrace();
 }finally {
  if(conn != null) {
  conn.disconnect();
  }
 }
 return result;
 }

如果checkDownload方法中能够正确获得资源，方法返回参数code=1，ajax成功执行：window.location.href = RootPath()+"/todownload?url="+filePath+"&name="+fileName;   调用（todownload)方法，传入url和name，执行文件下载。

 @RequestMapping("/todownload")
 @ResponseBody
 public void download(String url, String name, HttpServletResponse response) {
 HttpURLConnection conn = null;
 try {
  File file = new File(url);
  // 取得文件的后缀名。
  String ext = file.getName().substring(file.getName().lastIndexOf(".") + 1).toLowerCase();
  StringBuffer buffername = new StringBuffer(name);
  String filename = buffername.append(".").append(ext).toString();

  URL path = new URL(url);
  conn = (HttpURLConnection) path.openConnection();
  conn.setRequestMethod("GET");
  conn.setConnectTimeout(5 * 1000);
  InputStream fis = conn.getInputStream();// 通过输入流获取数据

  byte[] buffer = readInputStream(fis);
  if (null != buffer && buffer.length > 0) {
  // 清空response
  response.reset();
  // 设置response的Header
  response.addHeader("Content-Disposition","attachment;filename="+ new String((filename).getBytes("GBK"),"ISO8859_1"));
  response.addHeader("Content-Length", "" + buffer.length);
  OutputStream toClient = response.getOutputStream();
  response.setContentType("application/octet-stream");
  toClient.write(buffer);
  toClient.flush();
  toClient.close();
  }

 } catch (IOException ex) {
  ex.printStackTrace();
 }finally {
  if(conn != null) {
  conn.disconnect();
  }
 }
 }

  /**
   * 从输入流中获取数据
   * @param inStream 输入流
   * @return
   * @throws Exception
   */
 private byte[] readInputStream(InputStream fis) throws IOException {
  ByteArrayOutputStream outStream = new ByteArrayOutputStream();
     byte[] buffer = new byte[1024];
     int len = 0;
     while( (len=fis.read(buffer)) != -1 ){
       outStream.write(buffer, 0, len);
     }
     fis.close();
     return outStream.toByteArray();
 }

PS：Spring MVC 文件流形式下载(返回)视频文件

import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.URLEncoder;

/**
 * 文件流形式下载视频
 * @author Front Ng
 * @date 2019-05-23 09:25
 **/

@Controller
@RequestMapping(value = "/download")
@Api(value = "下载", tags = "下载")
public class DownloadController {

  @ApiOperation(value = "下载视频")
  @RequestMapping(method = RequestMethod.GET)
  public void download(HttpServletResponse response) throws IOException {

    File file = new File("/Users/front/Downloads/123.mp4");

    FileInputStream inputStream = new FileInputStream(file);
    byte[] data = new byte[(int) file.length()];
    int length = inputStream.read(data);
    inputStream.close();

    String fileName = URLEncoder.encode("文件流形式视频.mp4", "UTF-8");

    response.setContentType("application/octet-stream;charset=UTF-8");
    response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
    response.addHeader("Content-Length", "" + data.length);

    OutputStream stream = response.getOutputStream();
    stream.write(data);
    stream.flush();
    stream.close();
  }
}

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