Here is how one can configure transaction management in a java application with Spring framework.
Four cases will be explained and demonstrated:
- no transaction management
- local transaction with declarative configuration
- local transaction with programmatic approach
- distributed transaction with declarative configuration
- java 7
- maven 3
- any J2EE server (for example WildFly/JBoss)
Please, refer to source code at github
This application is a maven based web project.
For simple, local transactions single datasource is in use (this is a HSQLDB in memory instance). JUnit is more than enough to demonstrate how the code works.
It’s a bit more complicated with distributed transactions. First of all, another datasource is required - this is also a HSQLDB database. The code is called from a web controller - see distributed transaction section below.
Common code for all samples is represented by Service and DAO (and it’s implementations). Service is the major piece of our app, it updates both datasources, so someone (spring) has to manage all these updates in a single scope.
No transaction management
This is very basic use case: no specific configuration is submitted and datasource operates in auto-commit mode; all inserts are independent. Check sample unit test. Focus on testFail(): ltx.fail() will try to insert three records, with second record failing due to table constraints. But two other rows are still inserted. This is auto-commit.
Local transaction with declarative configuration
Let’s assume that our ltx.fail() should actually be in a transaction - if one of inserts fails, we want all of them to be rolled back as well. Here spring comes to play. Instead of making any changes to our code, we should just give spring specific instructions: when a transactions should be started and when it should be committed or rolled back.
Refer to spring configuration. To tell spring what to do, the config is using aop - aspect oriented programming. Basically, we tell to apply a rule (tx-advise), when a specific condition is met (app:config). In this case, our condition is a call to LocalTX instance (any method); and the rule is rollback when a Throwable is detected. I assume you know that any exception is a child of Throwable.
Check out this unit test. In this case, LocalTX instance is received from Spring and, actually, is a proxy. So when we are calling ltx.fail(), Spring knows that transaction has to be started. Our second insert in fail() is throwing DuplicateKeyException which is instance of Throwable; this triggers full rollback.
###Local transaction with programmatic approach
If, for some reason, AOP is not an option for your project, you can achieve the same result using hand-coded solution. Refer to LocalTXProgram - it’s pretty straight forward.
Distributed transaction management
Distributed transaction is a transaction which spans across multiple resources, e.g. two databases. Usual TRANSACTION BEGIN, COMMIT/ROLLBACK way is not working any more. The reason is in fault tolerance. It is always possible to find a sequence of events so that one datasource gets committed and other one gets rolled back.
Distributed transaction manager is required to make sure that all resources are either committed or rolled back. It is possible to use standalone manager, but for our example it’s way easier to use embedded one. All J2EE containers have one.
Refer to our spring mvc config. Major difference to all previous configs is declaration of JTATransactionManager. This manager gets connected by spring to an embedded one via jndi.
Take a look to this spring-tx source. When spring tries to discover existing service in JNDI, this list of names is used:
If no manager is found (for example, if WAR is deployed to a tomcat), you will get an error message:
To make sure JTA is available, the WAR should be deployed into J2EE server. For example, wildfly/jboss. Download full version, run it as standalone instance (bin/standalone.sh) and copy WAR to standalone/deployments. After the app is up and running, open test page: localhost:8080/transactions-example/test.do . Of course, the app can be deployed to any other J2EE server (e.g. weblogic)
In general, it works exactly the same as local transaction configuration. The only difference is use of JTA manager.
Worth mentioning, that the most common use case for distributed transaction is JMS + DATABASE. If a message from a jms source is not saved into a database, it should be put back.
Make sure you read about two-phase commit protocol.