DDevelopment & Design

OSGi Blueprint visualization

What is blueprint?Blueprint is a dependency injection framework for OSGi bundles. It could be written by hand or generated using Blueprint Maven Plugin. Blueprint file is only an XML describing beans, services and references. Each OSGi bundle could hav…

What is blueprint?

Blueprint is a dependency injection framework for OSGi bundles. It could be written by hand or generated using Blueprint Maven Plugin. Blueprint file is only an XML describing beans, services and references. Each OSGi bundle could have one or more blueprint files.

Blueprint files represent architecture of our bundle. Let’s visualize it using groovy script and graphviz available in my github repository and analyze.

Example generation

Pre: All you need is groovy and graphviz installed on your OS

I am working mostly with bundles with generated blueprint, so I will use blueprint file generated from Blueprint Maven Plugin tests as example. All examples are included in github repository.

Generation could be invoked by running run.sh script with given destination file prefix (png extension will be added to it) and path to blueprint file:

mkdir -p target

./run.sh target/fullBlueprint fullBlueprint.xml

Visualization is available here.

Separating domains

First if you look at the image, you see that some beans are grouped. You could easily extract such domains with tree roots: beanWithConfigurationProperties and beanWithCallbackMethods to separate blueprint files and bundles in future and generate images from them:

./run.sh target/beanWithCallbackMethods example/firstCut/beanWithCallbackMethods.xml
./run.sh target/beanWithConfigurationProperties example/firstCut/beanWithConfigurationProperties.xml
./run.sh target/otherStuff example/firstCut/otherStuff.xml

Now we have three, a bit cleaner, images: beanWithConfigurationProperties.png, beanWithCallbackMethods.png and otherStuff.png.

We also could generate image from more than one blueprint:

./run.sh target/joinFirstCut example/firstCut/otherStuff.xml example/firstCut/beanWithConfigurationProperties.xml example/firstCut/beanWithCallbackMethods.xml

And the result is here. The image contains beans grouped by file, but if you do not like it, you could force generation without such separation using option --no-group-by-file:

./run.sh target/joinFirstCutGrouped example/firstCut/otherStuff.xml example/firstCut/beanWithConfigurationProperties.xml example/firstCut/beanWithCallbackMethods.xml --no-group-by-file

It will generate image with all beans from all files.

Exclusion

Sometimes it is difficult to spot and extract other domains. It will be easier to do some experiments on blueprint. For example, bean my1 is a dependency for too many other beans. You could consider converting my1 bean to OSGi service and extracting it to another bundle.

Let’s exclude my1 bean from generation via -e option and see what happens:

./run.sh target/otherStuffWithoutMy example/firstCut/otherStuff.xml -e my1

Result is available here. Now we see, that tree with root bean myFactoryBeanAsService could be separated and my1 could be inject to it as osgi service in another bundle.

You could exclude more than one bean adding -e switch for each of them, e. g. -e my1 -e m2 -e myBean123.

Conclusion

Blueprint is great for dependency injection for OSGi bundles, but it is easy to create quite big context containing many domains. It is much easier to recognize or search for such domains using blueprint visualizer script.

 

YOUR CODE HRER

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DDevelopment & Design

JBoss Envers and Spring transaction managers

I've stumbled upon a bug with my configuration for JBoss Envers today, despite having integration tests all over the application. I have to admit, it casted a dark shadow of doubt about the value of all the tests for a moment. I've been practicing TDD since 2005, and frankly speaking, I should have been smarter than that.

My fault was simple. I've started using Envers the right way, with exploratory tests and a prototype. Then I've deleted the prototype and created some integration tests using in-memory H2 that looked more or less like this example:

@Test
public void savingAndUpdatingPersonShouldCreateTwoHistoricalVersions() {
    //given
    Person person = createAndSavePerson();
    String oldFirstName = person.getFirstName();
    String newFirstName = oldFirstName + "NEW";

    //when
    updatePersonWithNewName(person, newFirstName);

    //then
    verifyTwoHistoricalVersionsWereSaved(oldFirstName, newFirstName);
}

private Person createAndSavePerson() {
    Transaction transaction = session.beginTransaction();
    Person person = PersonFactory.createPerson();
    session.save(person);
    transaction.commit();
    return person;
}    

private void updatePersonWithNewName(Person person, String newName) {
    Transaction transaction = session.beginTransaction();
    person.setFirstName(newName);
    session.update(person);
    transaction.commit();
}

private void verifyTwoHistoricalVersionsWereSaved(String oldFirstName, String newFirstName) {
    List<Object[]> personRevisions = getPersonRevisions();
    assertEquals(2, personRevisions.size());
    assertEquals(oldFirstName, ((Person)personRevisions.get(0)[0]).getFirstName());
    assertEquals(newFirstName, ((Person)personRevisions.get(1)[0]).getFirstName());
}

private List<Object[]> getPersonRevisions() {
    Transaction transaction = session.beginTransaction();
    AuditReader auditReader = AuditReaderFactory.get(session);
    List<Object[]> personRevisions = auditReader.createQuery()
            .forRevisionsOfEntity(Person.class, false, true)
            .getResultList();
    transaction.commit();
    return personRevisions;
}

Because Envers inserts audit data when the transaction is commited (in a new temporary session), I thought I have to create and commit the transaction manually. And that is true to some point.

My fault was that I didn't have an end-to-end integration/acceptance test, that would call to entry point of the application (in this case a service which is called by GWT via RPC), because then I'd notice, that the Spring @Transactional annotation, and calling transaction.commit() are two, very different things.

Spring @Transactional annotation will use a transaction manager configured for the application. Envers on the other hand is used by subscribing a listener to hibernate's SessionFactory like this:

<bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean" >        
...
 <property name="eventListeners">
     <map key-type="java.lang.String" value-type="org.hibernate.event.EventListeners">
         <entry key="post-insert" value-ref="auditEventListener"/>
         <entry key="post-update" value-ref="auditEventListener"/>
         <entry key="post-delete" value-ref="auditEventListener"/>
         <entry key="pre-collection-update" value-ref="auditEventListener"/>
         <entry key="pre-collection-remove" value-ref="auditEventListener"/>
         <entry key="post-collection-recreate" value-ref="auditEventListener"/>
     </map>
 </property>
</bean>

<bean id="auditEventListener" class="org.hibernate.envers.event.AuditEventListener" />

Envers creates and collects something called AuditWorkUnits whenever you update/delete/insert audited entities, but audit tables are not populated until something calls AuditProcess.beforeCompletion, which makes sense. If you are using org.hibernate.transaction.JDBCTransaction manually, this is called on commit() when notifying all subscribed javax.transaction.Synchronization objects (and enver's AuditProcess is one of them).

The problem was, that I used a wrong transaction manager.

<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager" >
    <property name="dataSource" ref="dataSource"/>
</bean>

This transaction manager doesn't know anything about hibernate and doesn't use org.hibernate.transaction.JDBCTransaction. While Synchronization is an interface from javax.transaction package, DataSourceTransactionManager doesn't use it (maybe because of simplicity, I didn't dig deep enough in org.springframework.jdbc.datasource), and thus Envers works fine except not pushing the data to the database.

Which is the whole point of using Envers.

Use right tools for the task, they say. The whole problem is solved by using a transaction manager that is well aware of hibernate underneath.

<bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager" >
    <property name="sessionFactory" ref="sessionFactory"/>
</bean>

Lesson learned: always make sure your acceptance tests are testing the right thing. If there is a doubt about the value of your tests, you just don't have enough of them,