I have a Spring Boot CRUD application that has the Document class, which is a DB entity with a Blob field. I also have the DocumentWrapper class, which is a class that is used for the transmission of the document and has a MultiPartFile field.
So, Document is the entity that I am storing in the DB, and has a dedicated JPA repository, while DocumentWrapper is the "helper" entity that the controller accepts and returns.
So in my service layer, I perform a transformation between DocumentWrapper and Document types as follow, in order to use the DocumentRepository and using this class as Bean to perform the conversion:
@Configuration
public class DocumentWrapperConverter implements AttributeConverter<DocumentWrapper, Document>, Serializable {
@Autowired
private LobService lobService;
@Override
public DocumentWrapper convertToEntityAttribute(Document document) {
DocumentWrapper documentWrapper = new DocumentWrapper();
documentWrapper.setName(document.getName());
documentWrapper.setDescription(document.getDescription());
documentWrapper.setId(document.getId());
MultipartFile multipartFile = null;
try {
InputStream is = this.lobService.readBlob(document.getBlob());
multipartFile = new MockMultipartFile(document.getName(), document.getOriginalFilename(), document.getContentType().toString(), is);
} catch (IOException e) {
e.printStackTrace();
}
documentWrapper.setFile(multipartFile);
return documentWrapper;
}
@Override
public Document convertToDatabaseColumn(DocumentWrapper documentWrapper) {
Document document = new Document();
document.setName(documentWrapper.getName());
document.setDescription(documentWrapper.getDescription());
document.setId(documentWrapper.getId());
document.setContentType(documentWrapper.getContentType());
document.setFileSize(documentWrapper.getSize());
document.setOriginalFilename(documentWrapper.getOriginalFilename());
Blob blob = null;
try {
blob = this.lobService.createBlob(documentWrapper.getFile().getInputStream(), documentWrapper.getFile().getSize());
} catch (IOException e) {
e.printStackTrace();
}
document.setBlob(blob);
return document;
}
}
I encapsulated the logic to transform a Blob to an InputStream in the LobService and its implementor LobServiceImpl:
@Service
public class LobServiceImpl implements LobService {
@Autowired
private SessionFactory sessionFactory;
@Autowired
private DataSource dataSource;
@Transactional
@Override
public Blob createBlob(InputStream content, long size) {
return this.sessionFactory.getCurrentSession().getLobHelper().createBlob(content, size);
}
@Transactional
@Override
public InputStream readBlob(Blob blob) {
Connection connection = null;
try {
connection = this.dataSource.getConnection();
} catch (SQLException e) {
e.printStackTrace();
}
InputStream is = null;
try {
is = blob.getBinaryStream();
} catch (SQLException e) {
e.printStackTrace();
}
try {
assert connection != null;
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
return is;
}
}
This is my generic JPARepository interface:
@NoRepositoryBean
public interface GenericRepository<T extends JPAEntityImpl, S extends Serializable> extends JpaRepository<T, S> {}
Which is extended in my Document class:
@Repository
@Transactional
public interface DocumentRepository<T extends JPAEntityImpl, S extends Serializable> extends GenericRepository<Document, UUID> {
}
Also, the Document entity class:
@Entity
@Table(uniqueConstraints = {
@UniqueConstraint(columnNames = "id")
})
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.EXISTING_PROPERTY,
property = "typeName",
defaultImpl = Document.class)
public class Document extends JPAEntityImpl{
@Id
@Convert(converter = UUIDConverter.class)
@GeneratedValue(generator = "UUID")
@GenericGenerator(
name = "UUID",
strategy = "org.hibernate.id.UUIDGenerator"
)
@Column(nullable = false, unique = true)
protected UUID id;
@Column(length = 1000, nullable = false)
protected String name;
@Column(length = 1000, nullable = false)
protected String description;
@Column(length = 1000, nullable = true)
protected String originalFilename;
@Column(length = 1000, nullable = false)
protected MediaType contentType;
@Column
protected long fileSize;
@Column
@Lob
protected Blob blob;
public Document() {}
// GETTERS, SETTERS, TOSTRING....
And the DocumentWrapper entity class:
@JsonTypeInfo(
use = JsonTypeInfo.Id.NAME,
include = JsonTypeInfo.As.EXISTING_PROPERTY,
property = "typeName",
defaultImpl = DocumentWrapper.class)
public class DocumentWrapper extends JPAEntityImpl {
private UUID id;
private String name;
private String description;
private MultipartFile file;
public DocumentWrapper() {}
// GETTERS, SETTERS, TOSTRING....
I am having problems in the method public InputStream readBlob(Blob blob). The relevant part of the error log is the following:
org.postgresql.util.PSQLException: This connection has been closed.
at org.postgresql.jdbc.PgConnection.checkClosed(PgConnection.java:883)
at org.postgresql.jdbc.PgConnection.getLargeObjectAPI(PgConnection.java:594)
at org.postgresql.jdbc.AbstractBlobClob.getLo(AbstractBlobClob.java:270)
at org.postgresql.jdbc.AbstractBlobClob.getBinaryStream(AbstractBlobClob.java:117)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at org.hibernate.engine.jdbc.SerializableBlobProxy.invoke(SerializableBlobProxy.java:60)
at com.sun.proxy.$Proxy157.getBinaryStream(Unknown Source)
at org.ICIQ.eChempad.services.LobServiceImpl.readBlob(LobServiceImpl.java:42)
...
This line is the one which produces the Exception:
is = blob.getBinaryStream();
So, I would like to know how can I retrieve an InputStream for the Blob that I am receiving in the method public InputStream readBlob(Blob blob), so I can make the transformation between Document and DocumentWrapper. ¿How can I restore this connection that has been closed to retrieve the InputStream of the Blob? ¿Are there any workarounds?
Looking for answers on the Internet I saw many people performing this transformation using a ResultSet, but I am using a JPARepository interface to manipulate the records of Document in the database, not raw SQL queries; So I do not know how to proceed in that way.
I already tried using @Transactional annotations in this method but it did not work. I also tried setting the spring.jpa.properties.hibernate.current_session_context_class property (application.properties) to the values org.hibernate.context.ThreadLocalSessionContext, thread and org.hibernate.context.internal.ThreadLocalSessionContext but none of them worked.
I also tried to create a new connection, but it did not work.
I tried opening and closing a Session before and after calling blob.getBinaryStream(); but it did not work.
It seems to me that we need the same connection that was used to retrieve the Blob in the first place, but at some point Spring closes it and I do not know how to restore it or avoid that the connection is closed.
I also know that working with Byte[] arrays in my Document class could simplify things, but I do need to work with InputStream since I work with large files and is not convenient that whole files are loaded in memory.
If you need any other information about my code please do not hesitate to ask. I will add any required extra information.
Any tip, help or workaround is very welcome. Thank you.
Whatever method calls your DocumentWrapperConverter#convertToEntityAttribute probably also loads the data from the database. It should be fine to annotate this caller method with @Transactional to keep the Connection through the transaction alive. Note though, that you have to keep the connection open until you close the input stream, so you should probably push the bytes of the input stream to some sink within the transaction. Not sure if your MockMultipartFile consumes the input stream and stores the data into a byte[] or a temporary file, but that's what you will probably have to do for this to work.