DDevelopment & Design

Tired of exporting your OSGI metatype to client manually?

Feel my pain

We use OSGi, but we don’t deploy our bundles further than testing environment. It is our client who deploys it to production. However, they rarely read the metatypes – as metatype files are hidden deep inside jars and their format is not very user-friendly (who wants to read XMLs?). This is why they don’t know how to configure the application.

Sharing metatypes

If you work with OSGi metatype files, you have to find some way of informing your client what configuration is necessary for your application. There are a few ways of sharing this information:

  • You can send configuration options by e-mail or Jira/Redmine/(paste your issue tracker here). However, this might cause a big mess, searching is horrible, and it becomes outdated faster than you can say I hate sending metatypes.
  • You can share your repository with the client so that they always have up-to-date XMLs. Nevertheless, XML files are difficult to read and are scattered across whole modules.
  • You can keep your configuration in some document (e.g. Markdown), providing easy access for the client, but you must remember to synchronize it every time you change metatype.

metatype-exporter-maven-plugin to the rescue!

Our new Maven plugin allows us to automatically generate Markdown file from metatype files. Just add the plugin and enjoy automatically generated configuration created without any effort. Sample configuration may look like below.

<project ...>

    ...

    <pluginRepositories>
        <pluginRepository>
            <id>touk</id>
            <url>https://philanthropist.touk.pl/nexus/content/repositories/releases</url>
            <!-- we are not on central, but we are going to be there soon -->
        </pluginRepository>
    </pluginRepositories>
    <build>
        <plugins>
            <plugin>
                <groupId>pl.touk.osgi</groupId>
                <artifactId>metatype-exporter-maven-plugin</artifactId>
                <version>@metatype-exporter-maven-plugin.version@</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>export</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <destination>${project.build.directory}/classes/documentation</destination>
                    <outputFileName>ConfigurationDescription.md</outputFileName>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

 

Markdown produced by this configuration may look like this:

# Properties name (theseAreProperties) for pid this.is.first.pid

Description goes here

| ID  | Name  | Required | Type    | Default value | Options                         | Description |
| --- | ----- | -------- | ------- | ------------- | ------------------------------- | ----------- |
| id1 | name1 | Yes      | String  |               |                                 | desc1       |
| id2 |       | No       | Long    | 123           |                                 | desc2       |
| id3 |       | Yes      | Integer |               | <ul><li>15</li><li>30</li></ul> |             |

# Properties name (secondProps) for pid this.is.second.pid

| ID  | Required | Type   |
| --- | -------- | ------ |
| id1 | Yes      | String |

Markdown files are great because many git repositories like Gitlab or Github render Markdown files nicely. You can view the above file here: https://gist.github.com/piotrekfus91/ba36404341664c48df19576350a2340f.

Definitely more readable, huh?

Change language if your client doesn’t speak English

If you want to change the language of generated files, just add a resource bundle named MarkdownBundle, change locale in plugin configuration and enjoy your custom language. English and Polish are available out of the box.

<project ...>

    ...

    <build>
        <plugins>
            <plugin>
                <groupId>pl.touk.osgi</groupId>
                <artifactId>metatype-exporter-maven-plugin</artifactId>
                <version>@metatype-exporter-maven-plugin.version@</version>
                <executions>
                    <execution>
                        <goals>
                            <goal>export</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <language>de</language>
                    <country>DE</country>
                </configuration>
                <depenedencies>
                    <dependency>
                        <!-- maven coordinates of the jar with resource bundle -->
                    </dependency>
                <depenedencies>
            </plugin>
        </plugins>
    </build>
</project>

Resource bundle (for example MarkdownBundle_de.properties)

forPid=...
attributeHeaderId=...
attributeHeaderName=...
attributeHeaderDescription=...
attributeHeaderOptions=...
attributeHeaderType=...
attributeHeaderDefaultValue=...
attributeHeaderRequired=...
attributeRequiredTrue=...
attributeRequiredFalse=...

Summary

Our problem – client doesn’t know how to configure the application – was solved with our new Maven plugin. The sources may be found on https://github.com/TouK/metatype-exporter-maven-plugin.

What’s next?

We are planning to add other output formats or enable users to provide custom templates. If you have any suggestions for enhancements or found a bug, just let us know in a Github issue.

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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,