spring boot编写文件在线预览接口

以下是一个使用Spring Boot编写文件在线预览接口的示例：

1. 在`pom.xml`文件中添加以下依赖：

<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi</artifactId>
    <version>4.1.2</version>
</dependency>
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>poi-ooxml</artifactId>
    <version>4.1.2</version>
</dependency>
<dependency>
    <groupId>org.apache.pdfbox</groupId>
    <artifactId>pdfbox</artifactId>
    <version>2.0.21</version>
</dependency>

2. 编写一个控制器类，处理文件预览请求：

@RestController
@RequestMapping("/preview")
public class PreviewController {

    @GetMapping("/{fileName:.+}")
    public ResponseEntity<byte[]> previewFile(@PathVariable String fileName) throws IOException {
        String extension = FilenameUtils.getExtension(fileName);
        MediaType mediaType = MediaType.APPLICATION_OCTET_STREAM;
        if ("pdf".equalsIgnoreCase(extension)) {
            mediaType = MediaType.APPLICATION_PDF;
        } else if ("doc".equalsIgnoreCase(extension) || "docx".equalsIgnoreCase(extension)) {
            mediaType = MediaType.APPLICATION_MSWORD;
        } else if ("xls".equalsIgnoreCase(extension) || "xlsx".equalsIgnoreCase(extension)) {
            mediaType = MediaType.APPLICATION_EXCEL;
        } else if ("ppt".equalsIgnoreCase(extension) || "pptx".equalsIgnoreCase(extension)) {
            mediaType = MediaType.APPLICATION_POWERPOINT;
        }
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(mediaType);
        headers.setContentDisposition(ContentDisposition.builder("inline").filename(fileName).build());
        byte[] fileBytes = Files.readAllBytes(Paths.get(fileName));
        return new ResponseEntity<>(fileBytes, headers, HttpStatus.OK);
    }
}

3. 在`application.properties`文件中配置文件存储路径：

file.upload-dir=/path/to/uploaded/files/

4. 使用`MultipartFile`接收文件上传请求，保存文件到指定路径：

@PostMapping("/upload")
public ResponseEntity<String> uploadFile(@RequestParam("file") MultipartFile file) throws IOException {
    String fileName = file.getOriginalFilename();
    Path filePath = Paths.get(uploadDir + fileName);
    Files.write(filePath, file.getBytes());
    return ResponseEntity.ok("File uploaded successfully");
}

5. 在前端页面中使用`<iframe>`标签加载预览接口，例如：

<iframe src="/preview/example.pdf" width="100%" height="600"></iframe>

注意：本示例中只实现了对PDF、Word、Excel和PowerPoint文件的预览，如果需要支持其他类型的文件，需要根据实际情况进行修改。