How to pass a POJO to the SpringBoot application run method? - spring-boot

Question

I have this
#Bean public CommandLineRunner commandLineRunner(ApplicationContext ctx) {
// use a lambda expression to define a CommandLineRunner
return args -> {
... work ...
};
}
which is invoked like this
SpringApplication app = new SpringApplication(MyApp.class);
app.run(args); // perform configuration magic and invoke the above lambda function
This works great as long as the application was only used from the CLI. Now, the application is going through some refactoring to support a new run-time platform, and now I would like to do this:
app.run(complexOject); // pseudo-code, no such method in SpringApplication
i.e. I need to pass an ComplexObject to the application, while still preserving all the magic auto-configuration.
How can this be accomplished? Solutions with the least amount of code change are preferred.

Answer 1

The refactoring steps to enable a CommandLineRunner to receive arbitrary parameters is roughly as follows:
Move the guts (the ... work ... part) of the commandLineRunner method to a new method in a new bean class e.g. #Component public class GenericRunner { public void run(String ... args) ... }.
This is the most important step: Delete the original CommandLineRunner #Bean definition in its entirety. This will cause the application's run() method to exit after performing configuration.
Replace the app.run(args); invocation with the following
ConfigurableApplicationContext ctx = app.run(); // oh yeah
GenericRunner runner = ctx.getBean(GenericRunner.class);
runner.run(args);
Re-run all tests, commit the code changes.
The actual refactoring is now trivial: modify the runner.run(args) call at will. This is just a straight call into the GenericRunner POJO and is free of SpringBoot rules and limitations.

Answer 2

SpringApplication class obviously doesn't have a method that gets this output stream, its an entry point to the complicated by very powerful spring boot application loading process.
If the goal is to store the log of the application consider logging configuration rather than using output streams.
Otherwise please describe the requirement, what is the purpose of this output stream and I'll do my best to update this answer.
Update:
SpringApplication starts up an application context that is used as a registry for spring beans in the application.
So the most "spring friendly solution is to define a ComplexObject to be a spring bean, so that it will be injected into other beans that might need it.
This will work great if this bean can be created during the application startup.
Example:
class ComplexObject {...}
class ServiceThatMaintainsAReferenceOnObject {
private ComplexObject complexObject;
// all arg constructor
}
#Configuration
class SpringConfiguration {
#Bean
public ComplexObject complexObject() {
return new ComplexObject();
}
#Bean
public ServiceThatMaintainsAReferenceOnObject service(ComplexObject complexObject) {
return new ServiceThatMaintainsAReferenceOnObject(complexObject);
}
}
Now, if this complex object has to be created outside the spring application, maybe you need to pass it to some bean method as a parameter, after the application context is created. This can also be a case in the question, although it's definitely not a Spring way to do things.
Here is an example:
class ComplexObject {}
class Service {
void foo(ComplexObject complexObject);
}
#Configuration
class MyConfiguration {
#Bean
public Service service() {
return new Service();
}
}
// inside the main class of the application:
SpringApplication app = ...
ComplexObject complexObject = ... // get the object from somewhere
ApplicationContext ctx = app.run(args);
// by this time, the context is started and ready
Service service = ctx.getBean(Service.class);
service.foo(complexObject); // call the method on bean managed by spring
All in all, usually the second approach is not a regular use case of spring application, although its kind of feels like you're looking for something like this in the question.
All-in-all I think you should learn and understand how Spring works in a nutshell, and what exactly the ApplicationContext is to provide the best solution (I'm sorry for mentioning this, I said so because from the question it looks like you haven't really worked with Spring and don't really understand what does it do and how does it manage the application).