JarCastingtransaction-helper
End of life
This project is no longer maintained. The project is splitted into separate micro-projects:
- transaction-propagator-api: The API that contains the interface
- transaction-propagator-jta: The JTA based implementation of the API
- transaction-propagator-jta-ecm: Not yet implemented. This would be an OSGi component wrapper around the jta implementation of transaction-propagator
Introduction
Transaciton Helper is a OSGi-DS component that makes it simple to use transaction propagation in the code. The component registers the TransactionHelper OSGi service that has the well known propagation functions (requires, requiresNew, never, ...).
Differences between versions
Version 1.0.1
The versions 1.0.x (starting with 1.0.1) are Java 5 compatible. When an exception occures during a rollback or setRollbackOnly, that exception is logged with LogService.
Version 1.1.x and above
These versions use Throwable.addSuppressed(Throwable) function if an exception occures during rollback or setRollbackOnly. As throwable suppressions are only available since Java 7, these versions are compiled to be compatible with Java 7 and above.
From version 1.1.0 no LogService is necessary to use the TransactionHelper component.
Examples
Java 5
Integer result = transactionHelper.requiresNew(new Callback<Integer>() {
public Integer execute() {
// Do some stuff in the new transaction
}
});
Java 6 and Java 7
Integer result = transactionHelper.requiresNew(new Callback<Integer>() {
@Override
public Integer execute() {
// Do some stuff in the new transaction
}
});
Java 8 and above
Integer result = transactionHelper.requiresNew(() -> {
// Do some stuff in the new transaction
});
Usage without OSGi
There is a component in the bundle that registers TransactionHelper as an OSGi service. However, it is possible to use the solution without OSGi, as TransactionHelperImpl can be instantiated with any technology. After instantiation, the transactionManager of the framework must be provided for the TransactionHelperImpl via its setter method.
Why not annotations, interceptors or other magic?
By using this transaction helper, the trace of the code is always clear. We used Spring interceptors, Spring annotations, Aries interceptors in the past, but we decided not to use such "magical" solutions anymore.
Imagine the technology uses java proxies. In that case the programmer of the class cannot be sure in which way the call stack came. Did the call come from the same object but via a method that was not intercepted? Did it come via a method that was intercepted? As a solution, many programmers start intercepting all of the public methods of their class that is a very bad behavior.
Ok. We found out that there is ASM, CGLIB, whatever... We could use them to inherit from the class and with that, we can override all of the public and protected functions. Problem solved. Interception is done during all function call. What about the private functions?
Ok. We found out that there is Weaving. Private functions can be intercepted as well. It does not matter if the system starts up really slow. It does not matter that the hash of the class is not the same as it is at compile time.
What if I want to wrap a block of code inside an iteration with requiresNew transaction propagation? Do we really have to create a new function for that? And even if We do so, We cannot be sure that the new function is intercepted if the technology uses simple Java Proxy classes.
What about the bytecode compatibility? Will version X of ASM work with version Y of Java? Well, we saw it a couple of times that it did not. So we had to wait for a new version of ASM to be able to use a bugfix version of Java.
And especially in the OSGi world: What makes you sure that the bundle that does the weaving is started before your bundle that should be weaved?
Is it so much to ask to use an anonymous class? There will be more code, but still the code will be much more clear! It will be yours. With Java 8, the code will be even more nice if you use lambda expressions.
