Spring @Transactional on @Bean declaration instead of class Implementation

Question

I'd like to configure "transactional" beans from my Spring @Configuration class instead of annotating the class implementation itself with @Transactional.

Kind of like the old school way, configuring transactional advice from an XML file, but without needing a String reference to my class/method names to create pointcuts.

The reason is that the bean implementation is in another code base, and the module it belongs to doesn't depend on Spring. Read : I'm not touching the source code of that bean, just instanciating it. The class is final, can't extend it either to add Spring annotations to the child class. Let's say that all the methods must be transactional, for simplicity.

The bean implementation :

/** This class has no Spring dependency... */
// @Transactional <- which means I can't use this here
public final class ComplexComponentImpl implements ComplexComponent {

    private SomeRepository repo;

    public ComplexComponentImpl(SomeRepository repository) { this.repo = repository }

    public void saveEntities(SomeEntity e1, SomeEntity e2) {
        repo.save(e1);
        throw new IllegalStateException("Make the transaction fail");
    }

What I want to do in my configuration class (and which doesn't work in my unit test) :

@Configuration
@EnableTransactionManagement
public class ComplexComponentConfig {

    @Bean
    @Transactional // <- Make the bean transactional here
    public ComplexComponent complexComponent() {
        return new ComplexComponentImpl(repository());
    }

    // ...
}

The example above doesn't work, indeed, as nothing gets "transactional" at runtime : entity e1 is persisted even though the exception is thrown.

Note that my transaction management setup works works perfectly well with an implementation class marked with @Transactional.

Question : Is is it possible to declare @Beans transactional from a @Configuration class, or is there any alternative taking into accounts the constraints above ?

Answer 1

Found something built-in that is the sum of @Mecon's and @Erik Gillespie's answers, with limited boilerplate.

Spring already provides a TransactionProxyFactoryBean that just sets up a transactional proxy on any object. Much of the setup could be refactored to some utility method :

@Configuration
@EnableTransactionManagement
public class ComplexComponentConfig {

    /** NOT A @Bean, this object will be wrapped with a transactional proxy */
    public ComplexComponent complexComponentImpl() {
        return new ComplexComponentImpl(repository());
    }

    @Bean
    public ComplexComponent complexComponent() {
        TransactionProxyFactoryBean proxy = new TransactionProxyFactoryBean();

        // Inject transaction manager here
        proxy.setTransactionManager(txManager());

        // Define wich object instance is to be proxied (your bean)
        proxy.setTarget(complexComponentImpl());

        // Programmatically setup transaction attributes
        Properties transactionAttributes = new Properties();
        transactionAttributes.put("*", "PROPAGATION_REQUIRED");
        proxy.setTransactionAttributes(transactionAttributes);

        // Finish FactoryBean setup
        proxy.afterPropertiesSet();
        return (ComplexComponent) proxy.getObject;
    }

// ...
}