Rolling Back a Container-Managed Transaction

[http://java.sun.com/j2ee/tutorial/1_3-fcs/doc/Transaction3.html]

Rolling Back a Container-Managed Transaction

There are two ways to roll back a container-managed transaction. First, if a system exception is thrown, the container will automatically roll back the transaction. Second, by invoking the setRollbackOnly method of the EJBContext interface, the bean method instructs the container to roll back the transaction. If the bean throws an application exception, the rollback is not automatic, but may be initiated by a call to setRollbackOnly. For a description of system and application exceptions, see Handling Exceptions.

The source code for the following example is in the j2eetutorial/examples/src/ejb/bank directory. To compile the code, go to the j2eetutorial/examples directory and type ant bank. To create the database tables, type ant create-bank-table. A sample BankApp.ear file is in the j2eetutorial/examples/ears directory.

The transferToSaving method of the BankEJB example illustrates the setRollbackOnly method. If a negative checking balance occurs, transferToSaving invokes setRollBackOnly and throws an application exception (InsufficientBalanceException). The updateChecking and updateSaving methods update database tables. If the updates fail, these methods throw a SQLException and the transferToSaving method throws an EJBException. Because the EJBException is a system exception, it causes the container to automatically roll back the transaction. Here is the code for the transferToSaving method:

public void transferToSaving(double amount) throws
   InsufficientBalanceException  {

   checkingBalance -= amount;
   savingBalance += amount;

   try {
      updateChecking(checkingBalance);
      if (checkingBalance < 0.00) {
         context.setRollbackOnly();
         throw new InsufficientBalanceException();
      }
      updateSaving(savingBalance);
   } catch (SQLException ex) {
       throw new EJBException 
          ("Transaction failed due to SQLException: " 
          + ex.getMessage());
   }
}
 

When the container rolls back a transaction, it always undoes the changes to data made by SQL calls within the transaction. However, only in entity beans will the container undo changes made to instance variables. (It does so by automatically invoking the entity bean's ejbLoad method, which loads the instance variables from the database.) When a rollback occurs, a session bean must explicitly reset any instance variables changed within the transaction. The easiest way to reset a session bean's instance variables is by implementing the SessionSynchronization interface.