无法在springboot 2.0.2中使用GridFSFile写入磁盘

Question

尝试使用代码：

http://javasampleapproach.com/spring-framework/spring-data/springdata-mongodb-gridfstemplate-save-retrieve-delete-binary-files-image-text-files

使用springboot 1.5.13。 在此代码中检索图像使用GridFSDBFile，如下所示：

GridFSDBFile imageFile = gridOperations.findOne(new Query(Criteria.where("_id").is(imageFileId)));

以后保存在文件系统中使用：

imageFile.writeTo

Baeldung有相同的代码： http://www.baeldung.com/spring-data-mongodb-gridfs

我在springboot 2.0.2中有我的项目，这一行：

GridFSDBFile imageFile = gridOperations.findOne(new Query(Criteria.where("_id").is(imageFileId)));

抛出错误：

Type mismatch: cannot convert from GridFSFile to GridFSDBFile

所以，一旦我改为：

GridFSFile imageFile = gridOperations.findOne(new Query(Criteria.where("_id").is(imageFileId)));

没有错误，但现在我没有这个方法：

writeTo

写入磁盘。

更新1：

imageFileId = "5b0bff8b7cc45b32f43b47f4";

        GridFSFile imageFile = gridOperations.findOne(new Query(Criteria.where("_id").is(imageFileId)));
try {
            File file = new File("c:/JSA/retrieve/" + imageFile.getFilename());
            FileOutputStream streamToDownloadTo = new FileOutputStream(file);
            //This line doesn't works
            gridFSBucket.downloadToStream(imageFile.getId(), streamToDownloadTo);
            streamToDownloadTo.close();
        } catch (IOException e) {
            // handle exception
            System.out.println("error: " + e.getMessage());
        } catch (Exception e1) {
            System.out.println("error1: " + e1.getMessage());
        }

更新2：

try {
            File file = new File("c:/JSA/retrieve/" + imageFile.getFilename());
            FileOutputStream streamToDownloadTo = new FileOutputStream(file);
            System.out.println("imageFile.getId(): " + imageFile.getId());
            System.out.println("streamToDownloadTo: " + streamToDownloadTo.toString());
            gridFSBucket.downloadToStream(imageFile.getId(), streamToDownloadTo);
            streamToDownloadTo.close();
        } catch (IOException e) {
            // handle exception
            System.out.println("error: " + e.getMessage());
        } catch (Exception e1) {
            System.out.println("error1: " + e1.getMessage());
        }

控制台

imageFile.getId(): BsonObjectId{value=5b0bff8b7cc45b32f43b47f4}
streamToDownloadTo: java.io.FileOutputStream@3b20c8e2

此行抛出异常：

gridFSBucket.downloadToStream(imageFile.getId(), streamToDownloadTo);

并返回 null

解决

注入：

 @Autowired
    MongoGridFsTemplate mongoGridFsTemplate;


GridFSBucket gridFSBucket = GridFSBuckets.create(mongoGridFsTemplate.mongoDbFactory().getDb());
imageFileId = "5b0bff8b7cc45b32f43b47f4";

GridFSFile imageFile = gridOperations.findOne(new Query(Criteria.where("_id").is(new ObjectId(imageFileId))));

            try {
                File file = new File("c:/JSA/retrieve/" + imageFile.getFilename());
                FileOutputStream streamToDownloadTo = new FileOutputStream(file);
                gridFSBucket.downloadToStream(imageFile.getId(), streamToDownloadTo);
                streamToDownloadTo.close();
            } catch (IOException e) {
                // handle exception
                System.out.println("error: " + e.getMessage());
            } catch (Exception e1) {
                e1.printStackTrace();
            }