Integrate Guice component into Spring application

Question

We have a Spring framework based application and need to integrate a component that is built using Google Guice.

Can anybody give us some advice on how this can be

Answer 1

No Special framework or dependency is required to integrate guice component into spring-boot.

standard boot app

    @SpringBootApplication
    public class App {
       SpringApplication.run(App.class, appArgs);
    }

Guice module config

  @Configuration
  public class GuiceBeanConfig {

    private final Injector injector;

    // guice modules are initialized before the spring context completes 
    {
        injector = Guice.createInjector(
                new MyModuleA(),
                new MyModuleB()
        );
    }

    /**
     * Option1: can expose injector as a Spring Bean.
     */
    @Bean
    public Injector injector() {
        return injector;
    }


    /**
     * Option2: expose specific component as a Spring Bean.
     */
    @Bean
    public MyServiceA serviceA() {
        return injector.getInstance(ServiceA.class);
    }
}

Autowire into your service component as a regular spring bean.

• Option1: autowire guice injector and access any bean from it

   @Service
   public class MySpringService {
  
      private final ServiceA serviceA;  
  
      MySpringService (Injector i){
         serviceA = injector.getInstance(ServiceA.class)
      }
  
      public void callServiceA() {
          serviceA.doSomething();
      }
  
    }
  

• Option2: autowire specific bean

  @Service
  public class MySpringService {
  
    private final ServiceA serviceA; 
  
    MySpringService (ServiceA s){
        serviceA = s;
    }
  
    public void callServiceA() {
        serviceA.doSomething();
    }
  
  }
  

NOTE 1: By default Spring uses scope: Singleton and guice: Prototype. In case your guice component is not annotated as @Singleton :
Option1 creates an instance of ServiceA each time you create a new instance of MySpringService.
Option2 instead exposes ServiceA as a bean with scope Singleton.

Singleton vs Prototype: if you component/service is threadsafe, does not keep state the better option would be Singleton. Much better performance, less work for GC.

NOTE 2: Spring-boot does not require to use @Autowire annotation in case you do constructor injection.