Gist for Inversion of Control blog post. Find the blog post at https://pranjalgore.com/blog/

Application.java

//class in application.jar
@SpringBootApplication
@ComponentScan(basePackages= "com.plugin")  //scan classes in package com.plugin in plugin.jar
public class Application {

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}
	
  /*
  * concrete implementation of com.plugin.Contract.java
  * Spring will inject this bean into PluginApplication.java in plugin.jar
  */
	@Bean 
	public Contract contract() {
		return () -> {
			return "hello from application";
		};
	}

}

Contract.java

//interface in plugin.jar
public interface Contract {
	
	public String getMessageToPrint();

}

PluginApplication.java

//class in plugin.jar
@RestController
public class PluginApplication {
	
  /*
  * Spring will take care of finding the implementation of Contract interface
  * the developer need not ask for/find the implementation
  * the control of HOW this implementation is found is taken away from the developer and to the framework
  * hence, this is inversion of control
  */
	@Autowired
	private Contract contract;
	
	@GetMapping
	public String getThis() {
		return contract.getMessageToPrint();
	}

}