title: How to stream data to database BLOB using Hibernate (no in-memory storing in byte[])
body: <p>I'm looking for a way to stream binary data to/from database. If possible, i'd like it to be done with Hibernate (in database agnostic way).
  All solutions I've found involve explicit or implicit loading of binary data into memory as byte[]. I need to avoid it. Let's say I want my code to be able to write to a local file a 2GB video from database (stored in BLOB column), or the other way around, using no more than 256Mb of memory. It's clearly achievable, and involves no voodoo. But I can't find a way, for now I'm trying to avoid debugging Hibernate.</p>
  
  <p>Let's look at sample code (keeping in mind -Jmx=256Mb).</p>
  
  <p>Entity class:</p>
  
  <pre><code>public class SimpleBean {
      private Long id;
      private Blob data;
      // ... skipping getters, setters and constructors.
  }
  </code></pre>
  
  <p>Hibernate mapping fragment:</p>
  
  <pre><code>&lt;class name="SimpleBean" table="SIMPLE_BEANS"&gt;
      &lt;id name="id" column="SIMPLE_BEAN_ID"&gt;
          &lt;generator class="increment" /&gt;
      &lt;/id&gt;
      &lt;property name="data" type="blob" column="DATA" /&gt;
  &lt;/class&gt;
  </code></pre>
  
  <p>Test code fragment:</p>
  
  <pre><code>Configuration cfg = new Configuration().configure("hibernate.cfg.xml");
  ServiceRegistry serviceRegistry = new ServiceRegistryBuilder()
                                        .applySettings(cfg.getProperties())
                                        .buildServiceRegistry();
  
  SessionFactory sessionFactory = cfg.buildSessionFactory(serviceRegistry);
  Session session = sessionFactory.openSession();
  session.beginTransaction();
  
  File dataFile = new File("movie_1gb.avi");
  long dataSize = dataFile.length();
  InputStream dataStream = new FileInputStream(dataFile);
  
  LobHelper lobHelper = session.getLobHelper();
  Blob dataBlob = lobHelper.createBlob(dataStream, dataSize);
  
  session.save( new SimpleBean(data) );
  session.getTransaction().commit(); // Throws java.lang.OutOfMemoryError
  session.close();
  
  blobStream.close();
  sessionFactory.close();
  </code></pre>
  
  <p>When running that snippet I get OutOfMemory exception. Looking at stack trace shows what Hibernate tries to load the stream in memory and gets OutOfMemory (as it should). Here's stack trace:</p>
  
  <pre><code>java.lang.OutOfMemoryError: Java heap space
  at java.util.Arrays.copyOf(Arrays.java:2271)
  at java.io.ByteArrayOutputStream.grow(ByteArrayOutputStream.java:113)
  at java.io.ByteArrayOutputStream.ensureCapacity(ByteArrayOutputStream.java:93)
  at java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:140)
  at org.hibernate.type.descriptor.java.DataHelper.extractBytes(DataHelper.java:183)
  at org.hibernate.type.descriptor.java.BlobTypeDescriptor.unwrap(BlobTypeDescriptor.java:121)
  at org.hibernate.type.descriptor.java.BlobTypeDescriptor.unwrap(BlobTypeDescriptor.java:45)
  at org.hibernate.type.descriptor.sql.BlobTypeDescriptor$4$1.doBind(BlobTypeDescriptor.java:105)
  at org.hibernate.type.descriptor.sql.BasicBinder.bind(BasicBinder.java:92)
  at org.hibernate.type.AbstractStandardBasicType.nullSafeSet(AbstractStandardBasicType.java:305)
  at org.hibernate.type.AbstractStandardBasicType.nullSafeSet(AbstractStandardBasicType.java:300)
  at org.hibernate.type.AbstractSingleColumnStandardBasicType.nullSafeSet(AbstractSingleColumnStandardBasicType.java:57)
  at org.hibernate.persister.entity.AbstractEntityPersister.dehydrate(AbstractEntityPersister.java:2603)
  at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2857)
  at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3301)
  at org.hibernate.action.internal.EntityInsertAction.execute(EntityInsertAction.java:88)
  at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:362)
  at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:354)
  at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:275)
  at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:326)
  at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:52)
  at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1214)
  at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:403)
  at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
  at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175)
  at ru.swemel.msgcenter.domain.SimpleBeanTest.testBasicUsage(SimpleBeanTest.java:63)
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
  at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
  </code></pre>
  
  <p>Used Hibernate 4.1.5.SP1. The exact question is: how to avoid loading stream into memory when storing a blob in database using Hibernate, using direct streaming instead. I'd like to avoid off topics about why one stores video in column of database instead of storing it in some content repository and linking. Please, consider it a model what is irrelevant to the question.</p>
  
  <p>It seems that there might be some kind of capabilities on different dialects and Hibernate might try to load everything in memory, because underlying database doesn't support streaming blobs or something like that. If it's the case - i'd like to see some kind of comparative table between different dialects in aspect of handling blobs.</p>
  
  <p>Thank you very much for your help!</p>