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.
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