Type-safe customization of an existing application

The goal of this commit is to allow the configuration of an existing
application with type-safe configuration properties instead of using
error prone environment variables like now.

One of the design challenge is to be able to use configuration
properties in the DSL directly which is tricky because currently
they are beans and the context is not refreshed yet.

The proposed solution is to change
`inline fun <reified T : Any> configurationProperties(prefix: String = "")`
to
`inline fun <reified T : Any> configurationProperties(properties: T? = null, prefix: String = ""): T`
and to use `fun` instead of `val` for the application and the configuration.

Likely to be refined, but this is a major Kofu principle.

Closes spring-atticgh-228

Author: sdeleuze

autoconfigure-adapter/src/main/java/org/springframework/boot/context/properties/FunctionalConfigurationPropertiesBinder.java

@@ -41,10 +41,10 @@ public class FunctionalConfigurationPropertiesBinder {
 
 	public FunctionalConfigurationPropertiesBinder(ConfigurableApplicationContext context) {
 		this.context = context;
-		this.propertySources = new PropertySourcesDeducer(context).getPropertySources();
+		this.propertySources = new FunctionalPropertySourcesDeducer(context).getPropertySources();
 		this.binder = new Binder(ConfigurationPropertySources.from(propertySources),
         				new PropertySourcesPlaceholdersResolver(this.propertySources),
-        				new ConversionServiceDeducer(context).getConversionService(),
+        				null,
 				(registry) -> context.getBeanFactory().copyRegisteredEditorsTo(registry));
 	}
 

autoconfigure-adapter/src/main/java/org/springframework/boot/context/properties/FunctionalPropertySourcesDeducer.java

@@ -0,0 +1,42 @@
+package org.springframework.boot.context.properties;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
+import org.springframework.core.env.ConfigurableEnvironment;
+import org.springframework.core.env.Environment;
+import org.springframework.core.env.MutablePropertySources;
+import org.springframework.core.env.PropertySources;
+
+/**
+ * Similar to {@code PropertySourcesDeducer} without {@link PropertySourcesPlaceholderConfigurer}
+ * bean retrieval since application context is not refreshed yet.
+ * TODO Support property placeholder configuration
+ */
+public class FunctionalPropertySourcesDeducer {
+
+	private final ApplicationContext applicationContext;
+
+	FunctionalPropertySourcesDeducer(ApplicationContext applicationContext) {
+		this.applicationContext = applicationContext;
+	}
+
+	public PropertySources getPropertySources() {
+		MutablePropertySources sources = extractEnvironmentPropertySources();
+		if (sources != null) {
+			return sources;
+		}
+		throw new IllegalStateException("Unable to obtain PropertySources from "
+				+ "PropertySourcesPlaceholderConfigurer or Environment");
+	}
+
+	private MutablePropertySources extractEnvironmentPropertySources() {
+		Environment environment = this.applicationContext.getEnvironment();
+		if (environment instanceof ConfigurableEnvironment) {
+			return ((ConfigurableEnvironment) environment).getPropertySources();
+		}
+		return null;
+	}
+}

kofu/src/main/kotlin/org/springframework/fu/kofu/ConfigurationDsl.kt

@@ -41,16 +41,17 @@ open class ConfigurationDsl(private val dsl: ConfigurationDsl.() -> Unit): Abstr
 	}
 
 	/**
-	 * Specify the class and the optional prefix of configuration properties, which is the same mechanism than regular
-	 * [Spring Boot configuration properties mechanism](https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html#boot-features-external-config-typesafe-configuration-properties),
-	 * without `@ConfigurationProperties` annotation.
+	 * Bind and return the specified configuration properties class. If you need a bean,
+	 * register it via the [beans] DSL.
 	 *
 	 * @sample org.springframework.fu.kofu.samples.configurationProperties
 	 */
-	inline fun <reified T : Any> configurationProperties(prefix: String = "") {
-		context.registerBean("${T::class.java.simpleName.toLowerCase()}ConfigurationProperties") {
-			FunctionalConfigurationPropertiesBinder(context).bind(prefix, Bindable.of(T::class.java)).get()
+	inline fun <reified T : Any> configurationProperties(properties: T? = null, prefix: String = ""): T {
+		val properties = properties ?: FunctionalConfigurationPropertiesBinder(context).bind(prefix, Bindable.of(T::class.java)).get()
+		context.registerBean<T>("${T::class.java.simpleName.toLowerCase()}ConfigurationProperties") {
+			properties
 		}
+		return properties
 	}
 
 	/**

kofu/src/test/kotlin/org/springframework/fu/kofu/ApplicationDslTests.kt

@@ -77,12 +77,10 @@ class ApplicationDslTests {
 	@Test
 	fun `Application properties`() {
 		val app = application(WebApplicationType.NONE) {
-			configurationProperties<City>("city")
-		}
-		with(app.run()) {
-			assertEquals(getBean<City>().name, "San Francisco")
-			close()
+			val properties = configurationProperties<City>(prefix = "city")
+			assertEquals(properties.name, "San Francisco")
 		}
+		app.run().close()
 	}
 
 	@Test

kofu/src/test/kotlin/org/springframework/fu/kofu/samples/application.kt

@@ -31,31 +31,37 @@ private fun applicationDsl() {
 		beans {
 			bean<Foo>()
 		}
-		configurationProperties<City>("city")
+
 	}
 
 	fun main(args: Array<String>) = app.run()
 }
 
 private fun applicationDslWithConfiguration() {
-	val conf = configuration {
+	fun conf(cityName: String) = configuration {
 		beans {
 			bean<Foo>()
+			bean {
+				Bar(cityName)
+			}
 		}
 	}
-	val app = application(WebApplicationType.NONE) {
-		logging {
-			level = LogLevel.WARN
+	fun app(properties: CityProperties? = null) = application(WebApplicationType.NONE) {
+		with(configurationProperties(properties, prefix = "city")) {
+			logging {
+				level = LogLevel.WARN
+			}
+			enable(conf(name))
 		}
-		configurationProperties<City>("city")
-		enable(conf)
 	}
 
-	fun main(args: Array<String>) = app.run()
+	fun main(args: Array<String>) = app().run()
 }
 class Foo
 
-class City(val name: String, val country: String)
+class Bar(value: String)
+
+class CityProperties(val name: String, val country: String)
 
 interface UserRepository {
 	fun init()

kofu/src/test/kotlin/org/springframework/fu/kofu/samples/properties.kt

@@ -6,11 +6,12 @@ import org.springframework.fu.kofu.application
 fun configurationProperties() {
 	application(WebApplicationType.NONE) {
 
-		/** Will bind `sample.message` property typically defined in an `application.configurationProperties`
+		/** Bind `sample.message` property typically defined in an `application.properties`
 		 * or `application.yml` file to [SampleProperties.message]. Typically used by retrieving
 		 * a [SampleProperties] bean.
 		 */
-		configurationProperties<SampleProperties>(prefix = "sample")
+		val properties = configurationProperties<SampleProperties>(prefix = "sample")
+
 	}
 }
 

kofu/src/test/kotlin/org/springframework/fu/kofu/samples/webflux.kt

@@ -175,7 +175,7 @@ private fun webFluxApplicationDsl() {
 			level = LogLevel.INFO
 			level("org.springframework", LogLevel.DEBUG)
 		}
-		configurationProperties<City>(prefix = "city")
+		val city = configurationProperties<CityProperties>(prefix = "city")
 		enable(dataConfiguration)
 		enable(webConfiguration)
 	}

samples/kofu-coroutines-mongodb/src/main/kotlin/org/springframework/fu/sample/coroutines/Application.kt

@@ -3,10 +3,10 @@ package org.springframework.fu.sample.coroutines
 import org.springframework.boot.WebApplicationType
 import org.springframework.fu.kofu.application
 
-val app = application(WebApplicationType.REACTIVE)  {
+val app = application(WebApplicationType.REACTIVE) {
+	configurationProperties<SampleProperties>(prefix = "sample")
 	enable(dataConfig)
 	enable(webConfig)
-	configurationProperties<SampleProperties>("sample")
 }
 
 fun main() {

samples/kofu-coroutines-r2dbc/src/main/kotlin/com/sample/Application.kt

@@ -22,7 +22,7 @@ import org.springframework.fu.kofu.application
 
 @FlowPreview
 val app = application(WebApplicationType.REACTIVE) {
-	configurationProperties<SampleProperties>("sample")
+	configurationProperties<SampleProperties>(prefix = "sample")
 	enable(dataConfig)
 	enable(webConfig)
 }

samples/kofu-reactive-cassandra/src/main/kotlin/com/sample/Application.kt

@@ -20,15 +20,19 @@ import org.springframework.boot.WebApplicationType
 import org.springframework.fu.kofu.application
 import org.testcontainers.containers.CassandraContainer
 
-val app = application(WebApplicationType.REACTIVE) {
-	configurationProperties<SampleProperties>("sample")
-	enable(dataConfig)
-	enable(webConfig)
+fun app(properties: ApplicationProperties) = application(WebApplicationType.REACTIVE) {
+	with(configurationProperties(properties, prefix = "sample")) {
+		enable(dataConfig(cassandraHost, cassandraPort))
+		enable(webConfig(serverPort))
+	}
 }
 
 fun main() {
 	class KCassandraContainer : CassandraContainer<KCassandraContainer>() // https://github.com/testcontainers/testcontainers-java/issues/318
 	val cassandraContainer = KCassandraContainer().withInitScript("schema.cql")
 	cassandraContainer.start()
-	app.run(args = arrayOf("--cassandra.port=${cassandraContainer.firstMappedPort}", "--cassandra.host=${cassandraContainer.containerIpAddress}"))
+	val properties = ApplicationProperties(
+			cassandraHost = cassandraContainer.containerIpAddress,
+			cassandraPort = cassandraContainer.firstMappedPort)
+	app(properties).run()
 }