Java 大文件分片上传后端代码实现详解

以下是 Java 实现大文件分片上传的后端代码示例：

首先定义一个 RestController 类：

@RestController
public class FileUploadController {
    
    /**
     * 上传文件接口
     */
    @PostMapping('/upload')
    public ResponseEntity<?> uploadFile(@RequestParam('file') MultipartFile file,
                                        @RequestParam('chunkNumber') Integer chunkNumber,
                                        @RequestParam('totalChunks') Integer totalChunks,
                                        @RequestParam('chunkSize') Integer chunkSize,
                                        @RequestParam('identifier') String identifier,
                                        @RequestParam('filename') String filename) {
        // TODO: 实现文件上传逻辑
        return ResponseEntity.ok().build();
    }
}

在上传接口中，我们需要对上传的文件进行分片处理，将每个分片存储到临时文件夹中：

private void saveChunk(MultipartFile file, Integer chunkNumber, String identifier, String filename) throws IOException {
    String folderPath = '/tmp/' + identifier;
    File folder = new File(folderPath);
    if (!folder.exists()) {
        folder.mkdirs();
    }

    String chunkFilePath = folderPath + '/' + filename + '.part' + chunkNumber;
    FileOutputStream outputStream = new FileOutputStream(chunkFilePath);
    outputStream.write(file.getBytes());
    outputStream.close();
}

接着，我们需要编写一个合并分片的方法，将所有分片合并为完整的文件：

private void mergeChunks(String identifier, String filename) throws IOException {
    String folderPath = '/tmp/' + identifier;
    String filePath = folderPath + '/' + filename;
    File outputFile = new File(filePath);
    FileOutputStream outputStream = new FileOutputStream(outputFile);

    for (int i = 0; i < totalChunks; i++) {
        String chunkFilePath = folderPath + '/' + filename + '.part' + i;
        File inputFile = new File(chunkFilePath);
        FileInputStream inputStream = new FileInputStream(inputFile);

        byte[] buffer = new byte[1024];
        int len;
        while ((len = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, len);
        }

        inputStream.close();
        inputFile.delete();
    }

    outputStream.close();
    File folder = new File(folderPath);
    folder.delete();
}

最后，我们将上传接口中的逻辑完善，根据分片号码判断是否为最后一个分片，如果是则进行文件合并操作：

@PostMapping('/upload')
public ResponseEntity<?> uploadFile(@RequestParam('file') MultipartFile file,
                                    @RequestParam('chunkNumber') Integer chunkNumber,
                                    @RequestParam('totalChunks') Integer totalChunks,
                                    @RequestParam('chunkSize') Integer chunkSize,
                                    @RequestParam('identifier') String identifier,
                                    @RequestParam('filename') String filename) throws IOException {
    saveChunk(file, chunkNumber, identifier, filename);

    if (chunkNumber == totalChunks - 1) {
        mergeChunks(identifier, filename);
    }

    return ResponseEntity.ok().build();
}

注意：

代码中使用 /tmp 作为临时文件夹路径，请根据实际情况修改。
上述代码仅供参考，开发者可以根据实际需求进行修改和完善。