spring - GridFSDBFile 无法转换为 org.springframework.web.multipart.MultipartFile

Question

我正在编写一个 spring mvc webapp，它使用类型为 MultipartFile 的图像，我将其转换为 byte[] 然后转换为 Inputstream 和使用 GridFsTemplate 将其存储在 MongoDB 中。

现在的问题是我想在网页中显示存储的图像，但每当我尝试这样做时，数据库都会将图像文件作为 GridFSDBFiles 返回，因此抛出以下异常:

java.lang.ClassCastException: com.mongodb.gridfs.GridFSDBFile cannot be cast to org.springframework.web.multipart.MultipartFile

这是我用于存储图像的 DAO:

public void saveScan(Scan scan) throws IOException {

    String owner = String.valueOf(scan.getPatientId());

    String fileName = String.valueOf(scan.getPatientId() + "" + scan.getScanType());

    Date date = new Date();
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("MM/dd/YYYY HH:mm a");
    String uploadTime = simpleDateFormat.format(date);

    System.out.println("the scan type is " + scan.getScanType());

    DBObject metaData = new BasicDBObject();

    metaData.put("owner", owner);
    metaData.put("fileName", fileName);
    metaData.put("uploadTime", uploadTime);

    byte[] scanBytes = scan.getScan().getBytes();
    InputStream inputStream = new ByteArrayInputStream(scanBytes);
    scanDaoImpl.SaveScan(inputStream, fileName, "image/jpeg", metaData);
}

这是为了检索图像:

public MultipartFile findOneScan(BigInteger patientId) {

    MultipartFile multipartFile = (MultipartFile) gridFsTemplate
            .findOne(new Query(Criteria.where("metadata.owner").is(patientId)));
    return multipartFile;

这是我获取图像的 Controller

@ResponseBody
@RequestMapping(value = "/patients/{id}/scan", produces = MediaType.IMAGE_JPEG_VALUE)
public ResponseEntity<byte[]> scanImage(@PathVariable("id") BigInteger id) throws IOException {

    logger.debug("scanImage() is finding Image to display");

    byte[] bs = patientScanServiceImpl.findOne(id).getBytes();

    HttpHeaders httpHeaders = new HttpHeaders();
    httpHeaders.setContentType(MediaType.IMAGE_JPEG);
    httpHeaders.setCacheControl(CacheControl.noCache().getHeaderValue());

    return new ResponseEntity<byte[]>(bs, httpHeaders, HttpStatus.OK);
}

这是我的 thymeleaf 图片标签:

<span>
    <img th:src="@{/patients/{patientid}/scan(patientid=${patient.id})}" width="250" height="250"/>
</span>

Answer 1

现在我对此有了更多的了解，终于找到了解决办法。您不能直接将 gridFSDBFile 直接转换为 byte[ ]；它必须先转换为 OutputStream，然后如果必须显示，则转换为 byte[ ]。所以我允许我的 DAO 方法返回一个 GridFSDBFile 但在服务层我将 GridFSDBFile 转换为 ByteArrayOutputStream 然后到 byte[ ]。现在我的 DAO 检索图像的方法是

public GridFSDBFile findOneScan(BigInteger patientId, String scanType) {

    String fileName = String.valueOf(patientId + "" + scanType);

    GridFSDBFile gridFSDBFile = gridFsTemplate.findOne(new Query(Criteria.where("metadata.fileName").is(fileName)));
    return gridFSDBFile;

我为 Controller 提供服务的服务层是

public byte[] findOne(BigInteger patientId, String scanType) throws IOException {

    GridFSDBFile gridFSDBFile = scanRepository.findOneScan(patientId, scanType);
    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
    gridFSDBFile.writeTo(outputStream);
    byte[] bs = outputStream.toByteArray();

    return bs;
}

而且整个过程都很好。