Author: Dominik Przybysz

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 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

Do not use AllArgsConstructor in your public API

Introduction

Do you think about compatibility of your public API when you modify classes from it? It is especially easy to miss out that something incompatibly changed when you are using Lombok. If you use AllArgsConstructor annotation it will cause many problems.

What is the problem?

Let's define simple class with AllArgsConstructor: 
@Data
@AllArgsConstructor
public class Person {
    private final String firstName;
    private final String lastName;
    private Integer age;
}
Now we can use generated constructor in spock test: 
def 'use generated allArgsConstructor'() {
    when:
        Person p = new Person('John', 'Smith', 30)
    then:
        with(p) {
            firstName == 'John'
            lastName == 'Smith'
            age == 30
        }
}
And the test is green. Let's add new optional field to our Person class - email: 
@Data
@AllArgsConstructor
public class Person {
    private final String firstName;
    private final String lastName;
    private Integer age;
    private String email;
}
Adding optional field is considered compatible change. But our test fails... 
groovy.lang.GroovyRuntimeException: Could not find matching constructor for: com.github.alien11689.allargsconstructor.Person(java.lang.String, java.lang.String, java.lang.Integer)

How to solve this problem?

After adding field add previous constructor

If you still want to use AllArgsConstructor you have to ensure compatibility by adding previous version of constructor on your own: 
@Data
@AllArgsConstructor
public class Person {
    private final String firstName;
    private final String lastName;
    private Integer age;
    private String email;

    public Person(String firstName, String lastName, Integer age) {
        this(firstName, lastName, age, null);
    }
}
And now our test again passes.

Annotation lombok.Data is enough

If you use only Data annotation, then constructor, with only mandatory (final) fields, will be generated. It is because Data implies RequiredArgsConstructor: 
@Data
public class Person {
    private final String firstName;
    private final String lastName;
    private Integer age;
}
class PersonTest extends Specification {
    def 'use generated requiredFieldConstructor'() {
        when:
            Person p = new Person('John', 'Smith')
            p.age = 30
        then:
            with(p) {
                firstName == 'John'
                lastName == 'Smith'
                age == 30
            }
    }
}
After adding new field email test still passes.

Use Builder annotation

Annotation Builder generates for us PersonBuilder class which helps us create new Person: 
@Data
@Builder
public class Person {
    private final String firstName;
    private final String lastName;
    private Integer age;
}
class PersonTest extends Specification {
    def 'use builder'() {
        when:
            Person p = Person.builder()
                    .firstName('John')
                    .lastName('Smith')
                    .age(30).build()
        then:
            with(p) {
                firstName == 'John'
                lastName == 'Smith'
                age == 30
            }
    }
}
After adding email field test still passes.

Conclusion

If you use AllArgsConstructor you have to be sure what are you doing and know issues related to its compatibility. In my opinion the best option is not to use this annotation at all and instead stay with Data or Builder annotation. Sources are available here.