Transactions
A transaction is a group of several
operations that must behave atomically (i.e., as if they are a single,
indivisible operation). With regard to databases,
transactions allow you to combine one or more database actions into
a single atomic unit. If you have an application that needs to execute
multiple SQL statements to fulfill one goal (say an inventory
management system that needs to move items from an INVENTORY table to a SHIPPING table), you probably want to use
JDBC’s transaction services to accomplish the goal.
This section gives a brief overview of transactions with respect to relational databases and JDBC. For broader coverage of transactions in the general J2EE environment, see Chapter 16.
Working with a transaction involves the following steps: start
the transaction, perform its component operations, and then either
commit the transaction if all the component operations succeed or roll
it back if one of the operations fails. The ability to roll back a
transaction is the key feature. This means that if any one SQL
statement fails, the entire operation fails, and it is as though none
of the component operations took place. Therefore, it is impossible to
end up with a situation in which, for example, the INVENTORY table has been debited, but the
SHIPPING table has not been
credited.
Another issue with transactions and databases concerns changes to the database becoming visible to the rest of the system. Transactions can operate at varying levels ...
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