How to reference a bean by type in a SpEL?

Question

The following is a minimal example, showing my problem.

Main.kt:

package com.mycompany.configurationpropertiestest

import org.slf4j.LoggerFactory
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.boot.context.properties.ConfigurationProperties
import org.springframework.boot.context.properties.ConstructorBinding
import org.springframework.boot.context.properties.EnableConfigurationProperties
import org.springframework.boot.runApplication
import org.springframework.scheduling.annotation.EnableScheduling
import org.springframework.scheduling.annotation.Scheduled
import org.springframework.stereotype.Service


@SpringBootApplication
@EnableScheduling
@EnableConfigurationProperties(FooServiceConfig::class)
class Application

fun main(args: Array<String>) {
    runApplication<Application>(*args)
}


@ConstructorBinding
@ConfigurationProperties("configurationpropertiestest.foo")
data class FooServiceConfig(
    val interval: Int = 1000,
    val message: String = "hi"
)


@Service
class FooService(
    private val myConfig: FooServiceConfig
) {
    private val log = LoggerFactory.getLogger(this.javaClass)
    //@Scheduled(fixedDelayString = "#{@FooServiceConfig.interval}")
    //@Scheduled(fixedDelayString = "#{@myConfig.interval}")
    @Scheduled(fixedDelayString = "\${configurationpropertiestest.foo.interval}")
    fun talk() {
        log.info(myConfig.message)
    }
}

(@ConstructorBinding is used to allow having the members of FooServiceConfig immutable.)

application.yml:

configurationpropertiestest:
  foo:
    interval: 500
    message: "hi"

Test.kt:

package com.mycompany.configurationpropertiestest

import org.junit.Test
import org.junit.runner.RunWith
import org.springframework.boot.test.context.SpringBootTest
import org.springframework.test.context.junit4.SpringRunner


@RunWith(SpringRunner::class)
@SpringBootTest
class Test {
    @Test
    fun `sit and wait`() {
        Thread.sleep(3000)
    }
}

It works, but it only does, because I reference interval in the @Scheduled annotation like so:

@Scheduled(fixedDelayString = "\${configurationpropertiestest.foo.interval}")

This somewhat breaks the nicely isolated configuration of my service. It suddenly has to know about external things, which it should now need to know about.

Ideally, it would only access its configuration either by the type of the bean:

@Scheduled(fixedDelayString = "#{@FooServiceConfig.interval}")

or by the injected instance:

@Scheduled(fixedDelayString = "#{@myConfig.interval}")

But these attempts result in No bean named 'FooServiceConfig' available and No bean named 'myConfig' available respectively.

Any idea of how I can achieve to access only the config bean and not the global config value?

Answer 1

If you don't mind making FooService.myConfig public, this should work:

@Service
class FooService(val myConfig: FooServiceConfig) {

    val log = LoggerFactory.getLogger(this.javaClass)

    @Scheduled(fixedDelayString = "#{@fooService.myConfig.interval}")
    fun talk() {
        log.info(myConfig.message)
    }
}

UPDATE:

Apparently Spring changes the names of the beans annotated with the @ConstructorBinding annotation to [configuration-properties-value]-[fully-qualified-bean-name]. FooServiceConfig ends up as configurationpropertiestest.foo-com.mycompany.configurationpropertiestest.FooServiceConfig

So, despite being quite ugly, this should work as well:

@Service
class FooService(private val myConfig: FooServiceConfig) {

    val log = LoggerFactory.getLogger(this.javaClass)

    @Scheduled(fixedDelayString = "#{@'configurationpropertiestest.foo-com.mycompany.configurationpropertiestest.FooServiceConfig'.interval}")
    fun talk() {
        log.info(myConfig.message)
    }
}

Finally, the last option, answering the title question: How to reference a bean by type in a SpEL? You can do it by calling beanFactory.getBean:

@Service
class FooService(private val myConfig: FooServiceConfig) {

    val log = LoggerFactory.getLogger(this.javaClass)

    @Scheduled(fixedDelayString = "#{beanFactory.getBean(T(com.mycompany.configurationpropertiestest.FooServiceConfig)).interval}")
    fun talk() {
        log.info(myConfig.message)
    }
}

Answer 2

I changed a little your code and for me it working. Main change was inject FooServiceConfig with @Autowired. Then in scheduler I could write: "#{@fooServiceConfig.interval}"

@SpringBootApplication
@EnableScheduling
class Application

fun main(args: Array<String>) {
    SpringApplication.run(Application::class.java, *args)
}

@Configuration
@EnableConfigurationProperties
@ConfigurationProperties("configurationpropertiestest.foo")
data class FooServiceConfig(
        var interval: Int = 1000,
        var message: String = "hi"
)

@Service
class FooService {
    private val log = LoggerFactory.getLogger(this.javaClass)

    @Autowired
    lateinit var fooServiceConfig:FooServiceConfig

    @Scheduled(fixedDelayString = "#{@fooServiceConfig.interval}")
    fun talk() {
        log.info(fooServiceConfig.message)
    }
}

UPDATE

If you need @ConstructorBinding you can access to its values in other way. Introduce other config class that for example extract interval value and expose it as a new bean. After that you can refer to this bean later in @Scheduled

@Configuration
class DelayConfig{

    @Bean(name = ["talkInterval"])
    fun talkInterval(fooServiceConfig: FooServiceConfig): Int {
        return fooServiceConfig.interval
    }
}

@Service
class FooService(
        private val myConfig: FooServiceConfig
) {
    private val log = LoggerFactory.getLogger(this.javaClass)

    @Scheduled(fixedDelayString = "#{@talkInterval}")
    fun talk() {
        log.info(myConfig.message)
    }
}