[英]How to select BLOB in chunks using Hibernate and write to a File?
我需要选择Blob数据并将其写入磁盘上的文件。 我需要使用从Blob获得的Binary Stream来执行此操作,但是我正面临OutOfMemoryError,我找不到解决它的方法。
实体类:
@Entity
@Table(name = "Table1")
public class AttachmentData implements Serializable
{
// member variables
@Column(name = "CONTENT")
@Lob
private Blob content;
// getters, setters
}
实现类:
EntityManagerFactory emf = Persistence.createEntityManagerFactory("default");
EntityManager em = emf.createEntityManager();
EntityTransaction et = em.getTransaction();
et.begin();
Session session = (Session) em.getDelegate(); // hibernate session
attachmentData = (AttachmentData) session.get(AttachmentData.class, new Long(1000));
InputStream is = attachmentData.getContent().getBinaryStream();
FileOutputStream fos = new FileOutputStream(new File("D:\\MyFile.wmv"));
BufferedOutputStream bos = new BufferedOutputStream(fos);
byte buf[] = new byte[2048];
int len;
while ((len = is.read(buf)) > 0)
{
bos.write(buf, 0, len);
bos.flush();
}
使用Hibernate 4.2.1和JPA 1。
这是我如何使其工作的方法:
Session session = (Session) em.getDelegate(); // hibernate session
session.doWork(new Work()
{
@Override
public void execute(Connection connection) throws SQLException
{
try
{
String QUERY_STATEMENT = "SELECT * FROM Table1 WHERE ID= ?";
PreparedStatement preparedStatement = connection.prepareStatement(QUERY_STATEMENT);
preparedStatement.setLong(1, new Long(123123));
ResultSet rs = preparedStatement.executeQuery();
while (rs.next())
{
String fileName = rs.getString("FILE_NAME");
FileOutputStream outStream = new FileOutputStream(location + fileName);
InputStream inStream = rs.getBinaryStream("CONTENT");
try
{
IOUtils.copy(inStream, outStream);
}
catch (Exception exc)
{
exc.printStackTrace();
}
finally
{
IOUtils.closeQuietly(outStream);
IOUtils.closeQuietly(inStream);
}
}
}
catch (Exception exc)
{
exc.printStackTrace();
}
}
});
问题是MSSQL驱动程序将整个数据加载到byte []中,而不是向我提供流。 我正在使用Oracle和MSSQL数据库。 这为两者提供了通用的解决方案。
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