gridFSBucket.downloadToStream(fileId, fileOutputStream)转MultipartFile Java代码

可以通过以下代码将 GridFSBucket 下载的文件转换为 MultipartFile：

import com.mongodb.client.gridfs.GridFSBucket;
import com.mongodb.client.gridfs.GridFSDownloadStream;
import org.springframework.web.multipart.MultipartFile;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.UUID;

public class GridFsToMultipartFileConverter {

    public static MultipartFile convert(GridFSBucket gridFsBucket, String fileId, String fileName) throws IOException {
        GridFSDownloadStream downloadStream = gridFsBucket.openDownloadStream(fileId);
        byte[] bytes = new byte[(int) downloadStream.getGridFSFile().getLength()];
        downloadStream.read(bytes);
        InputStream inputStream = new ByteArrayInputStream(bytes);
        return new MultipartFile() {
            @Override
            public String getName() {
                return fileName;
            }

            @Override
            public String getOriginalFilename() {
                return fileName;
            }

            @Override
            public String getContentType() {
                return downloadStream.getGridFSFile().getMetadata().getString("contentType");
            }

            @Override
            public boolean isEmpty() {
                return bytes.length == 0;
            }

            @Override
            public long getSize() {
                return bytes.length;
            }

            @Override
            public byte[] getBytes() throws IOException {
                return bytes;
            }

            @Override
            public InputStream getInputStream() throws IOException {
                return inputStream;
            }

            @Override
            public void transferTo(java.io.File file) throws IOException, IllegalStateException {
                throw new UnsupportedOperationException();
            }
        };
    }
}

使用方法：

MultipartFile multipartFile = GridFsToMultipartFileConverter.convert(gridFsBucket, fileId, fileName);