Transactions and Transaction Managers

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2 Transactions and Transaction Managers There are many transactional resources Databases Messaging middleware As programmers, we want abstract transactions: we do not want to deal with some transaction API specific to only Oracle or DB2 we might want to be able to have in one transaction: several operations with several databases several operations with several messaging providers Declarative Transactions 2

3 Transaction Managers Transaction Managers (TM) provide us with such abstract transactions TM hides any complexities and API differences of particular transactional resources TM provides for programmer unified transaction API In Java EE these (unified) APIs are: Java Transaction API (JTA) is meant for Software System programmers Java Transaction Service (JTS) is meant for Application Server implementers Declarative Transactions 3

4 How to use Java Transaction API Client managed transactions client programmer directly calls JTA API Component managed transactions client is unaware of transactions, component programmer calls JTA API Container managed transaction neither client nor component programmer calls JTA API, container does it automatically Also known as declarative transactions Declarative Transactions 4

5 Client-managed transactions Declarative Transactions 5

6 Component-managed transactions Declarative Transactions 6

7 Container-managed transactions Declarative Transactions 7

8 Container-managed transactions: Transaction attributes Declarative Transactions 8

9 Container-managed transactions: Transaction attribute Required Transactional attribute Required: If a client invokes the component s method while the client is associated with a transaction context, the container invokes the component s method in the client s transaction context. If the client invokes the component s method while the client is not associated with a transaction context, the container automatically starts a new transaction before delegating a method call to the component s method. If the business method invokes other components, the container passes the transaction context with the invocation. The container attempts to commit the transaction when the method that started the transaction has completed. Declarative Transactions 9

10 Container-managed transaction example Client R Comp1 R Required RN RequiresNew Transaction context R Comp2 RN Comp5 R RN R Comp3 Comp4 Comp6 Declarative Transactions 10

11 public class TellerBean implements Teller private EntityManager public void transferfunds(long amount, String fromaccount, String toaccount) { // Load entities from DB: BankAccount ba1=em.find(bankaccount.class, fromaccount); BankAccount ba2=em.find(bankaccount.class, toaccount); } ba1.withdraw(amount); ba2.deposit(amount); Declarative Transactions 11

12 Distributed transactions - example In the following figure, a client invokes the enterprise bean X. Bean X updates data using two database connections A and B. Then X calls another enterprise bean, Y. Bean Y updates data in database C. The Application Server (TM actually) ensures that the updates to databases A, B, and C are either all committed or all rolled back. Declarative Transactions 12

13 Distributed transactions - example Declarative Transactions 13

14 Distributed transactions - example The application programmer does not have to do anything to ensure transactional semantics. Behind the scenes, the TM enlists the database connections as part of the transaction. When the transaction commits, the TM and the database systems perform a two-phase commit protocol to ensure atomic updates across all three databases. Declarative Transactions 14

15 Distributed transactions example Two-phase commit protocol makes it possible to perform the updates to databases A and B in a single transaction Declarative Transactions 15

16 Client-managed transactions Declarative Transactions 16

17 What about.net? Also has declarative transactions:.net Windows Communication Foundation (WCF) Transactions introduced in.net 3.0 and built on top of System.Transactions available in.net 2.0. Provides a declarative approach to transaction management that is implemented using various attributes and properties, such as: TransactionScopeRequired, TransactionAutoComplete, and TransactionFlow Declarative Transactions 17