客户端下载服务端实例代码

1. 将文件以流的形式一次性读取到内存，通过响应输出流输出到前端

/**
* @param path 想要下载的文件的路径
* @param response
* @功能描述 下载文件:
*/
@RequestMapping("/download")
public void download(String path, HttpServletResponse response) {
try {
// path是指想要下载的文件的路径
File file = new File(path);
log.info(file.getPath());
// 获取文件名
String filename = file.getName();
// 获取文件后缀名
String ext = filename.substring(filename.lastIndexOf(".") + 1).toLowerCase();
log.info("文件后缀名：" + ext);
 
// 将文件写入输入流
FileInputStream fileInputStream = new FileInputStream(file);
InputStream fis = new BufferedInputStream(fileInputStream);
byte[] buffer = new byte[fis.available()];
fis.read(buffer);
fis.close();
 
// 清空response
response.reset();
// 设置response的Header
response.setCharacterEncoding("UTF-8");
//Content-Disposition的作用：告知浏览器以何种方式显示响应返回的文件，用浏览器打开还是以附件的形式下载到本地保存
//attachment表示以附件方式下载 inline表示在线打开 "Content-Disposition: inline; filename=文件名.mp3"
// filename表示文件的默认名称，因为网络传输只支持URL编码的相关支付，因此需要将文件名URL编码后进行传输,前端收到后需要反编码才能获取到真正的名称
response.addHeader("Content-Disposition", "attachment;filename=" + URLEncoder.encode(filename, "UTF-8"));
// 告知浏览器文件的大小
response.addHeader("Content-Length", "" + file.length());
OutputStream outputStream = new BufferedOutputStream(response.getOutputStream());
response.setContentType("application/octet-stream");
outputStream.write(buffer);
outputStream.flush();
} catch (IOException ex) {
ex.printStackTrace();
}
} 

2、将输入流中的数据循环写入到响应输出流中，而不是一次性读取到内存，通过响应输出流输出到前端

/**
* @param path 指想要下载的文件的路径
* @param response
* @功能描述 下载文件:将输入流中的数据循环写入到响应输出流中，而不是一次性读取到内存
*/
@RequestMapping("/downloadLocal")
public void downloadLocal(String path, HttpServletResponse response) throws IOException {
// 读到流中
InputStream inputStream = new FileInputStream(path);// 文件的存放路径
response.reset();
response.setContentType("application/octet-stream");
String filename = new File(path).getName();
response.addHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(filename, "UTF-8"));
ServletOutputStream outputStream = response.getOutputStream();
byte[] b = new byte[1024];
int len;
//从输入流中读取一定数量的字节，并将其存储在缓冲区字节数组中，读到末尾返回-1
while ((len = inputStream.read(b)) > 0) {
outputStream.write(b, 0, len);
}
inputStream.close();
} 

3、下载网络文件到本地

/**
* @param path 下载后的文件路径和名称
* @param netAddress 文件所在网络地址
* @功能描述 网络文件下载到服务器本地
*/
@RequestMapping("/netDownloadLocal")
public void downloadNet(String netAddress, String path) throws IOException {
URL url = new URL(netAddress);
URLConnection conn = url.openConnection();
InputStream inputStream = conn.getInputStream();
FileOutputStream fileOutputStream = new FileOutputStream(path);
 
int bytesum = 0;
int byteread;
byte[] buffer = new byte[1024];
while ((byteread = inputStream.read(buffer)) != -1) {
bytesum += byteread;
System.out.println(bytesum);
fileOutputStream.write(buffer, 0, byteread);
}
fileOutputStream.close();
} 

4.下载服务器文件到本地

package com.llp.response;
import javax.servlet.ServletContext;
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.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
public class FileDownServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       // 1.获取下载文件的路径**
        String realPath="E:\\target\\classes\\ddl.txt";
        System.out.println("下载文件路径"+realPath);
       // 2.下载的文件名
        String fileName=realPath.substring(realPath.lastIndexOf("\\"+1));
       // 3.设置让浏览器支持所下载的文件(设置中文编码utf-8格式)
        resp.setHeader("Content-Disposition", "attachment;filename="+ URLEncoder.encode(fileName, "utf-8"));
       // 4.获取下载文件的输入流
        FileInputStream in= new FileInputStream(realPath);
       // 5.创建缓冲区
        int len=0;
        byte[] buffer=new byte[1024];
        // 6.获取OutputStream对象
        ServletOutputStream out=resp.getOutputStream();
       // 7.将FileOutputStream流写入到buffer缓冲区
       // 8.使用OutputStream将缓冲区中的数据输入到客户端
        while((len=in.read(buffer))>0){
            out.write(buffer,0,len);
        }
        in.close();
        out.close();
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

5. 网络文件获取到服务器后，经服务器处理后响应给前端

/**
* @param netAddress
* @param filename
* @param isOnLine
* @param response
* @功能描述 网络文件获取到服务器后，经服务器处理后响应给前端
*/
@RequestMapping("/netDownLoadNet")
public void netDownLoadNet(String netAddress, String filename, boolean isOnLine, HttpServletResponse response) throws Exception {
 
URL url = new URL(netAddress);
URLConnection conn = url.openConnection();
InputStream inputStream = conn.getInputStream();
 
response.reset();
response.setContentType(conn.getContentType());
if (isOnLine) {
// 在线打开方式 文件名应该编码成UTF-8
response.setHeader("Content-Disposition", "inline; filename=" + URLEncoder.encode(filename, "UTF-8"));
} else {
//纯下载方式 文件名应该编码成UTF-8
response.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(filename, "UTF-8"));
}
 
byte[] buffer = new byte[1024];
int len;
OutputStream outputStream = response.getOutputStream();
while ((len = inputStream.read(buffer)) > 0) {
outputStream.write(buffer, 0, len);
}
inputStream.close();
} 

参考：

https://blog.csdn.net/aaa58962458/article/details/120764754

https://blog.csdn.net/weixin_55491446/article/details/122951047