software from the trenches

Oracle BLOBs have traditionally been a pain to deal with because of driver issues. It’s frustrating to work on a project where a lot of effort is directed toward overcoming technical problems instead of concentrating on the real problem domain – implementing a custom Hibernate UserType for mapping a BLOB to a byte[] is one such example.


Spring has a concept of a pluggable LobHandler, a strategy interface for its data access framework that allows for custom handling of BLOBs and CLOBs where necessary. The standard LobHandler usage scenario is handing it to Spring JDBC code that executes SQL or calls a stored procedure, but you can also use it when configuring a SessionFactory:

<bean id="sessionFactory"
  class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
  <property name="dataSource" ref="dataSource" />
  <property name="lobHandler">
    <bean class="org.springframework.jdbc.support.lob.OracleLobHandler">
      <property name="nativeJdbcExtractor">
        <bean class="org.springframework.jdbc.support.nativejdbc.CommonsDbcpNativeJdbcExtractor" />
      </property>
    </bean>
  </property>
  ... etc. ...
</bean>

Then, in the mapping file for the domain object that needs to map bytes to a BLOB, you can use the out-of-the-box BlobByteArrayType:

<!-- Make sure to use bytecode instrumentation for per-property lazy loading! -->
<property name="myByteArrayProperty"
  type="org.springframework.orm.hibernate3.support.BlobByteArrayType"
  lazy="true">
  <column name="SOME_BLOB" />
</property>

It’s like anything else: use what’s already there instead of reinventing the wheel to keep your code simple and relevant to the real problem you’re trying to solve.