Useful Links & tips

Optimistic Lock gives more control on concurrent modification on data. That can be achieved very easily in hibernate using @Version column. But in some cases we may have to avoid concurrency check, example background process. To disable Optimistic lock set OptimisticLockMode as NONE for entity class while hibernate is initiating. We can't remove version column that needs Database changes and ORM changes. In this way we can disable Optimistic Lock by code. implement "org.hibernate.event.Initializable" interface override the below method.     @Override     public void initialize(Configuration cfg) {         Iterator<?> persistentClassIterator = cfg.getClassMappings();         while (persistentClassIterator.hasNext()) {             PersistentClass persistentClass = PersistentClass.class.cast(persistentClassIterato...

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Hibernate have option to check concurrent modification of a same data. Which will be easy when we add a version column in the table and hibernate entity. If existing row has version as NULL then hibernate will throw the NullPointerException while updating the existing data. To avoid this exception   @version column  should be NOT NULL and should have a default value. if it number 1.

Using PropertyFile task we can edit the property file during ANT build. Edit property value are very easy and can find here details. http://ant.apache.org/manual/Tasks/propertyfile.html but delete a property or comment a property is the tricky one. If we are using latest ant version (1.8.1 or later), we can delete a property like below. <propertyfile file="my.properties" comment="My properties">   < entry  key="propertykey" operation="del"/> < /propertyfile> but the older version that is before 1.8.1 don't have operation called " del ", if we run the command in lower version ant, we will get a error says undefined operation "del".      there is workaround instead deleting a property we can comment that property using ant's replace command. < replace file="sample.properties">                      < replacefilter token="propertykey" value="#propert...

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Hibernate has two options for locking Optimistic and Pessimistic. Optimistic Locking has more advantage over pessimistic by performance and etc,. To achieve  Optimistic Locking is very as adding a annotation for a field.  For more details read here..  http://docs.jboss.org/hibernate/orm/4.0/devguide/en-US/html/ch05.html#d0e2225  

This exception will occur when we use @Version for Optimistic Locking. This error means somewhere in the code same entity(table) has modified twice in same transaction or separate. In my situation we had manual flush, after removing that manual flush this error gone.