Dependency Injection with dynamically instanciated class with Spring Boot

Question

I'm trying to develop a spring-boot application which offer the possibility for the user to create and call some simple workflows.

The steps of the workflows are already written (they all extends the same class), and, when the user create a workflow, he/she just pick which steps he wants to include in his it. The steps and the workflows are saved in a database.

My problem comes when the user call the workflow: I want to instanciate dynamically each step using the class loader but with the dependencies injected by spring!

Here is an example of a plug-in:

public class HelloWorldStepPlugin extends StepPlugin {

    private static final Logger LOG = LogManager.getLogger();

    @Autowired
    private HelloWorldRepository repository;

    public HelloWorldStepPlugin() {
        super(HelloWorldStepPlugin.class.getSimpleName());
    }

    @Override
    public void process() {
        LOG.info("Hello world!");
        this.repository.findAll(); // <= throw a NullPointerException because this.repository is null
    }

}

Here is how I execute a Workflow (in another class):

ClassLoader cl = getClass().getClassLoader();
for (Step s : workflow.getSteps()) {
    StepPlugin sp = (StepPlugin) cl.loadClass(STEP_PLUGIN_PACKAGE + s.getPlugin()).newInstance();
    sp.process();
}

How can I do to have my HelloWorldRepository injected by Spring? Is there a much better approach to do what I intend to?

Answer 1

I suggest you declare your steps as prototype beans. Instead of saving class names in the database, save bean names. Then get the steps and the plugins from the spring context (i.e. using getBean()).