Functional Spring Boot

About Me

John Burns

In the Beginning...

XML

Spring Boot

@SpringBootApplication
@EnableWebMvc
public class MyApplication {
}
@Service
public class MyBusinessLogic {
    public String doSomething();
}
@RestController
public class MyController {
    private final MyBusinessLogic service;
    @Autowired
    public MyController(MyBusinessLogic service) {
        this.service = service;
    }
    @GetMapping(path = "/ping")
    public String get() {
        return service.doSomething();
    }
}
                

Spring Boot: The Good

• No XML
• Wiring lives closer to code
• Less boilerplate

Spring Boot: The Bad

• Learning Curve
• Performance
• Structureless

Eliminate Component Scan

@SpringBootConfiguration
@EnableAutoConfiguration
@EnableWebMvc
public class MyApplication {
    @Bean
    MyBusinessLogic myBusinessLogic() {
        return MyBusinessLogic();
    }
    @Bean
    MyController myController(MyBusinessLogic myBusinessLogic) {
        return MyController(myBusinessLogic);
    }
}
public class MyBusinessLogic {
    public String doSomething();
}
@RestController
public class MyController {
    private final MyBusinessLogic service;
    public MyController(MyBusinessLogic service) {
        this.service = service;
    }
    @GetMapping(path = "/ping")
    public String get() {
        return service.doSomething();
    }
}
                

Remaining Issues

• Still need AutoConfiguration
• Still using Annotations
• Boilerplate

Programmatic Configuration

• Slightly more boilerplate
• Much easier to reason about
• Tests are very fast
• App Startup is very fast

Spring Fu

• Converts all Autoconfigs to Initializers
• Provides DSLs
• All-in
• Spring pivoted to hints for graalvm

Beans Dsl

val beans = beans {
    bean<MyBusinessLogic>()
    bean<MyBusinessLogicWithInjection> {
        MyBusinessLogicWithInjection(ref())
    }
    bean<MyBusinessLogicWithInjectionByName>("beanName") {
        MyBusinessLogicWithInjectionByName(ref("name"))
    }
}

Router Dsl

class MyBusinessLogic {
    fun doSomething(request: ServerRequest): ServerResponse
}
val myRoutes(service: MyBusinessLogic) = router {
    GET("/ping", service::doSomething)
    POST("/ping", service::doSomethingElse)
}

Functional Spring

val myRoutes(service: MyBusinessLogic) = router {
    GET("/ping", service::doSomething)
}
val beans = beans {
    bean<MyBusinessLogic>()
    bean(::myRoutes)
}
@SpringBootConfiguration
@EnableAutoConfiguration
@EnableWebMvc
open class MyApplication
  : ApplicationContextInitializer<GenericApplicationContext> {
    override fun initialize(context: GenericApplicationContext) {
        beans.initialize(context)
    }
}
class MyBusinessLogic {
    public String doSomething();
}

Functional Spring 7.x

val myRoutes(service: MyBusinessLogic) = router {
    GET("/ping", service::doSomething)
}
@SpringBootConfiguration
@EnableAutoConfiguration
@EnableWebMvc
@Import(SampleBeanRegistrar::class)
open class MyApplication {
}
class MyBusinessLogic {
    public String doSomething();
}
class SampleBeanRegistrar : BeanRegistrarDsl({
    registerBean<MyBusinessLogic>()
    registerBean(::myRoutes)
})

Remaining Issues

• Still need AutoConfiguration
• Not extensible

Spring Funk

open class MyApplication : SpringFunkApplication {
    override fun dsl(): SpringDslContainer.() -> Unit = {
        beans {
            bean<MyBusinessLogic>()
        }
        webmvc {
            enableWebMvc {
                jetty()
            }
            routes {
                router { service: MyBusinessLogic -> {
                        GET("/ping", service::doSomething)
                    }
                }
            }
        }
    }
}
class MyBusinessLogic {
    public String doSomething();
}

Demo

Resources

Spring Docs

Spring Fu

Spring Funk

Sébastien Deleuze Demo