Totally confused - @Component vs @Configurable

[Radish]

Hi,

I've got a class that looks something like this:

@Configurable
public class ChangeQuantityTransaction extends AbstractTransaction
{
  @Override
  @Transactional
  public Object doTransaction(MapSqlParameterSource params) throws Exception
  {
     a few sql updates are performed in here
  }
}

AbstractTransaction class looks like this:

public abstract class AbstractTransaction
{
  protected JdbcTemplate _jt;

  public Object doTransaction(MapSqlParameterSource params) throws Exception;

  @Autowired
  protected void setDataSource(DataSource dataSource)
  {
    _jt = new JdbcTemplate(dataSource);     
  }
}

Configuration (admin-servlet.xml):

<bean id="changeQuantityTransaction" class="mypackage.ChangeQuantityTransaction" />

<bean class="org.springframework.web.context.support.ServletContextAttributeExporter"
  <property name="attributes">
    <map>
      <entry key="changeQuantityTrans">
        <ref bean="changeQuantityTrans" />
      </entry>
    </map>
  </property>
</bean>

I am working with a legacy servlet and get a changeQuantityTransaction in the servlet's init method:

private ChangeQuantityTransaction _trans;
public void init(ServletConfig config)
{
  Object obj = config.getServletContext().getAttribute("changeQuantityTrans");
  setTransaction((ChangeQuantityTransaction)obj);
}

private void setTransaction(ChangeQuantityTransaction trans)
{
  _trans = trans;
}

Here is the confusing part. When I annotate ChangeQuantityTransaction with @Configurable, the method setDataSource (in the abstract parent) is called only once. If I annotate the class with @Component, setDataSource is called twice.

Why do the different annotations cause setDataSource to be called a different number of times? Looking at the Spring debug output I can see the bean is created as a singleton, but I don't see why it is being initialized twice, and I can't find anything in the reference material that tells me why @Configurable and @Component would behave in a different manner.

Another question - which annotation is better here, @Configurable or @Component?

Thanks,

Paul

[Marten Deinum]

Is it called on the same instance or is it simply called twice. I suspect that you have component-scanning enabled, which would lead to double instantiation of your bean. Also why would you want to use @Configurable or @Component, as you already specified the bean in xml...