springboot实现文件上传下载

Spring Boot提供了简单易用的方式来处理文件上传和下载功能。下面是一个简单的示例：

1. 创建一个文件上传的控制器

@RestController
public class FileUploadController {

    private static final Logger logger = LoggerFactory.getLogger(FileUploadController.class);

    @PostMapping("/upload")
    public String uploadFile(@RequestParam("file") MultipartFile file) {
        try {
            // 保存文件
            byte[] bytes = file.getBytes();
            Path path = Paths.get(file.getOriginalFilename());
            Files.write(path, bytes);

            logger.info("文件上传成功：" + file.getOriginalFilename());
            return "文件上传成功：" + file.getOriginalFilename();
        } catch (IOException e) {
            logger.error("文件上传失败：" + e.getMessage());
            return "文件上传失败：" + e.getMessage();
        }
    }

}
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2. 创建文件下载的控制器

@RestController
public class FileDownloadController {

    private static final Logger logger = LoggerFactory.getLogger(FileDownloadController.class);

    @GetMapping("/download")
    public ResponseEntity<Resource> downloadFile() {
        try {
            // 加载文件资源
            Resource resource = new UrlResource("file:test.txt");
            String filename = resource.getFilename();
            String contentType = Files.probeContentType(Paths.get(filename));

            return ResponseEntity.ok()
                    .contentType(MediaType.parseMediaType(contentType))
                    .header(HttpHeaders.CONTENT_DISPOSITION, "attachment; filename=\"" + filename + "\"")
                    .body(resource);
        } catch (IOException e) {
            logger.error("文件下载失败：" + e.getMessage());
            return ResponseEntity.notFound().build();
        }
    }

}
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3. 在应用程序中配置文件上传和下载的细节。

#文件上传配置
spring.servlet.multipart.enabled=true
spring.servlet.multipart.max-file-size=10MB
spring.servlet.multipart.max-request-size=10MB
spring.servlet.multipart.file-size-threshold=0
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@Configuration
public class AppConfig implements WebMvcConfigurer {

    //文件上传配置
    @Bean
    public MultipartResolver multipartResolver() {
        CommonsMultipartResolver resolver = new CommonsMultipartResolver();
        resolver.setDefaultEncoding("UTF-8");
        resolver.setMaxUploadSize(10485760);
        resolver.setMaxInMemorySize(4096);
        return resolver;
    }

    //文件下载配置
    @Bean
    public ByteArrayResource byteArrayResource() {
        return new ByteArrayResource(new byte[0]);
    }

    @Override
    public void addResourceHandlers(ResourceHandlerRegistry registry) {
        registry.addResourceHandler("/file/**")
                .addResourceLocations("file:/usr/local/data/");
    }

}
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4. 在页面上传文件

<form th:action="@{/upload}" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <button type="submit">上传文件button>
form>
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5. 在页面下载文件

<a th:href="@{/download}" download="test.txt">下载文件a>
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这样就实现了文件上传和下载功能。当用户上传文件时，文件将被保存在应用程序的根目录中。当用户下载文件时，文件将从文件系统中加载并作为响应传输。