web server - Borland Technical Publications

Handling of EJB exceptions
Handling of EJB exceptions
If a global transaction is associated with the current thread of execution do not use this
method. If the global transaction is not a container-managed transaction, that is the
application manages its own transactions, and a rollback is required use the JTA API to
perform the rollback rather than invoking rollback() directly on the JDBC connection.
Java.sql.Connection.close()
As defined in the JDBC API, this method closes the database connection and all JDBC
resources associated with the connection.
If the thread is associated with a transaction this call simply notifies the JDBC pool that
work on the connection is complete. The JDBC pool releases the connection back to
the connection pool once the transaction has completed. JDBC connections opened by
the JDBC pool cannot be closed explicitly by an application.
Java.sql.Connection.setAutoCommit(boolean)
As defined in the JDBC API, this method is used to set the auto commit mode of a
transaction. The setAutoCommit() method allows Java applications to either:
■
Execute and commit all SQL statements as individual transactions (when set to
true). This is the default mode, or
■
Explicitly invoke commit() or rollback() on the connection (when set to false).
If the thread is associated with a transaction, the JDBC pool turns off the auto-commit
mode for all connections factoried in the scope of a partition's transaction service
transaction. This is because the transaction service must control transaction
completion. If an application is involved with a transaction, and it attempts to set the
auto commit mode to true, the java.sql.SQLException() will be raised.
Enterprise JavaBeans can throw application and/or system level exceptions if they
encounter errors while handling transactions. Application-level exceptions pertain to
errors in the business logic and are intended to be handled by the calling application.
System-level exceptions, such as runtime errors, transcend the application itself and
can be handled by the application, the bean, or the bean container.
The EJB declares application-level exceptions and system-level exceptions in the
throws clauses of its Home and Remote interfaces. You must check for checked
exceptions in your program try/catch block when calling bean methods.
System-level exceptions
An EJB throws a system-level exception, which is a java.ejb.EJBException (but may
also be a java.rmi.RemoteException), to indicate an unexpected system-level failure.
For example, it throws this exception if it cannot open a database connection. The
java.ejb.EJBException is a runtime exception and does not have to be listed in the
throws clause of the bean's business methods.
System-level exceptions usually require the transaction to be rolled back. Often, the
container managing the bean does the rollback. Other times, especially with beanmanaged
transactions, the client must rollback the transaction.
Chapter 19: Transaction management 179