目的：为了解决前端直接根据文件连接地址下载导致的跨域问题；后端提供一个接口，根据前端传入的文件地址链接下载文件到本地再返回文件流给前端，从而避免跨域问题（代码已上线）

controller层代码：

import org.springframework.core.io.Resource;
import org.springframework.core.io.UrlResource;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;public class controller{@ApiOperation("下载文件")@GetMapping("/front/downloadFile")public ResponseEntity<Resource> downloadFile(@RequestParam String fileUrl) {try {Path downloadedFile = xxService.downloadFile(fileUrl);Resource resource = new UrlResource(downloadedFile.toUri());HttpHeaders headers = new HttpHeaders();headers.add(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=" + resource.getFilename());return ResponseEntity.ok().headers(headers).contentLength(resource.contentLength()).contentType(MediaType.APPLICATION_OCTET_STREAM).body(resource);} catch (Exception e) {log.error("下载文件异常，源文件地址是: {}。 异常信息是：{}", fileUrl, e.getMessage());return ResponseEntity.status(500).body(null);}}}   

xxService层代码：

    @Overridepublic Path downloadFile(String fileUrl) throws Exception {URL url = new URL(fileUrl);URLConnection connection = url.openConnection();String fileName = determineFileName(fileUrl);Path tempFile = Files.createTempFile("downloaded", ".tmp");Files.copy(connection.getInputStream(), tempFile, StandardCopyOption.REPLACE_EXISTING);Path targetFile = tempFile.resolveSibling(fileName);// 该方法会move临时文件转换为目标文件Files.move(tempFile, targetFile, StandardCopyOption.REPLACE_EXISTING);log.info("文件下载成功后的保存路径是：{}", targetFile.toAbsolutePath());return targetFile;}private String determineFileName(String fileUrl) {String[] parts = fileUrl.split("/");String fileName = parts[parts.length - 1];if (fileName.contains(".")) {return fileName;} else {return fileName + ".tmp"; // 默认添加 .tmp 扩展名}}

如果使用postman测试该接口，则会直接下载该接口；