【springboot】实现文件上传和下载

1. 新建一个springboot项目

      新建一个springboot项目，选择web，默认即可.

      主要pom配置文件如下：

<parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.2.10.RELEASE</version><relativePath/> <!-- lookup parent from repository --></parent><properties><maven.compiler.source>11</maven.compiler.source><maven.compiler.target>11</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><!--web包--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency></dependencies>
<!--    maven打包设置--><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId><configuration><includeSystemScope>true</includeSystemScope></configuration><executions><execution><goals><goal>repackage</goal></goals></execution></executions></plugin></plugins></build>

2. 配置文件

      在配置文件中配置文件上传和下载的根目录，文件大小限制等。

application.properties

file.upload.url=path/to/upload
# 文件大小限制
spring.servlet.multipart.max-file-size=10MB 
# 请求大小限制
spring.servlet.multipart.max-request-size=20MB

application.yml

file.upload.url: path/to/upload
spring:servlet:multipart:# 文件大小限制max-file-size: 10MBmax-request-size: 20MB

3. 控制类实现文件上传和下载

      在控制类中实现文件上传和下载。其中，文件上传通过MultipartFile实现文件类型限制、文件大小限制、多文件上传等，下载通过文件流实现。

@RestController
@RequestMapping(value = "/file")
@CrossOrigin // 允许跨域
@ControllerAdvice // 全局异常处理
public class FileController {//上传的根目录@Value("${file.upload.url}")private String uploadFilePath;@Value("${file.upload.url}")private String downloadFilePath;//捕获上传文件过大的异常//@ExceptionHandler标识方法将处理指定类型的异常@ExceptionHandler(MaxUploadSizeExceededException.class)public ResponseEntity<String> handleMaxSizeException(MaxUploadSizeExceededException exc) {return ResponseEntity.status(HttpStatus.PAYLOAD_TOO_LARGE).body("文件过大，请重新选择上传图片！");}@RequestMapping("/upload")public String httpUpload(@RequestParam("files")//MultipartFile 是 Spring 框架中用于处理文件上传的接口MultipartFile files[]) {StringBuffer urls = new StringBuffer();//遍历多个文件for (int i = 0; i < files.length; i++) {//获取文件类型String contentType = files[i].getContentType();System.out.println(contentType);if (!contentType.contains("image")) {return "文件格式不正确，请重新选择图片！";}//获取上传文件的后缀名String postfix = files[i].getOriginalFilename().substring(files[i].getOriginalFilename().lastIndexOf("."));//生成文件名 使用时间戳，避免重名String fileName = System.currentTimeMillis()+postfix;System.out.println(fileName);
//            File dest = new File(uploadFilePath + '/' + fileName);File dest = new File(uploadFilePath + '/' + fileName);//目录不存在则创建目录if (!dest.getParentFile().exists()) {dest.getParentFile().mkdirs();}try {//将上传的文件保存到指定的目标位置files[i].transferTo(dest);} catch (Exception e) {return "程序错误，请重新上传\n" + e.toString();}urls.append("\n"+uploadFilePath + '\\' + fileName);}return "文件上传成功" + urls.toString();}@RequestMapping("/download")public String fileDownLoad(HttpServletResponse response, @RequestParam("fileName") String fileName) {
//        File file = new File(downloadFilePath + '/' + fileName);File file = new File(downloadFilePath + '\\' + fileName);if (!file.exists()) {return "下载文件不存在";}//清除之前设置的内容response.reset();//设置响应内容类型为二进制流response.setContentType("application/octet-stream");//设置响应字符编码为UTF-8response.setCharacterEncoding("utf-8");//设置响应文件大小response.setContentLength((int) file.length());//设置浏览器以附件的形式下载，并设置文件名response.setHeader("Content-Disposition", "attachment;filename=" + fileName);try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));) {byte[] buff = new byte[1024];OutputStream os = response.getOutputStream();int i = 0;while ((i = bis.read(buff)) != -1) {os.write(buff, 0, i);os.flush();}} catch (IOException e) {return "下载失败";}return "下载成功";}
}

4. 测试

      以下测试使用工具postman实现。测试文件大小的图片可以使用代码生成，可参考文章。

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参考链接：

https://cloud.tencent.com/developer/article/1594124

https://cloud.baidu.com/article/2773207

https://blog.csdn.net/m0_63297090?type=blog