The import com. Mongo. Client. Gridfs. GridFSBucket; 
The import com. Mongo. Client. Gridfs. GridFSDownloadStream; 
The import com. Mongo. Client. Gridfs. Model. GridFSFile; 
import org.apache.commons.io.IOUtils; 
The import org. Bson. Types. The ObjectId; 
import org.junit.Test; 
The import org. Junit. Runner. RunWith; 
The import org. Springframework. Beans. Factory. The annotation. Autowired; 
The import org. Springframework. Boot. Test. The context. SpringBootTest; 
The import org. Springframework. Data. The mongo. Core. Query. The Criteria; 
The import org. Springframework. Data. The mongo. Core. Query. The query; 
The import org. Springframework. Data. The mongo. Gridfs. GridFsResource; 
The import org. Springframework. Data. The mongo. Gridfs. GridFsTemplate; 
The import org. Springframework. Test. The context. Takeup. SpringRunner; 

import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import java.io.IOException; 

@ SpringBootTest 
@ RunWith (SpringRunner class) 
Public class GridFsTest {

The @autowired 
Private GridFsTemplate GridFsTemplate; 

The @autowired 
Private GridFSBucket GridFSBucket; 



//take file 
@ Test 
Public void queryFile () throws IOException {

//according to the id file 
GridFSFile GridFSFile=gridFsTemplate. FindOne (Query. The Query (Criteria) where (" _id ") is (" 5 ec8cea13cc2be46e01a0e65 "))); 

//open a download stream objects 
GridFSDownloadStream GridFSDownloadStream=gridFSBucket. OpenDownloadStream (gridFSFile getObjectId ()); 
//create GridFsResource object, obtain flow 
GridFsResource GridFsResource=new GridFsResource (gridFSFile gridFSDownloadStream); 
//data from flow 
The String content=IOUtils. ToString (gridFsResource getInputStream (), "utf-8"); 
System.out.println(content); 


} 


} 

An error prompt: org. Bson. BsonInvalidOperationException: the Value expected to be of type DOCUMENT is of unexpected type STRING