[sb-@Value] @Value inject in Kotlin

spring-boot-kotlin/src/main/kotlin/com/baeldung/theValueAnnotation/KotlinValueInjectionApplication.kt

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+package com.baeldung.theValueAnnotation
+
+import org.springframework.boot.SpringApplication
+import org.springframework.boot.autoconfigure.SpringBootApplication
+import org.springframework.context.annotation.PropertySource
+
+
+@PropertySource(value = ["classpath:application-inject-value.yml"], factory = YamlPropertySourceFactory::class)
+@SpringBootApplication(scanBasePackages = ["com.baeldung.theValueAnnotation"])
+class KotlinValueInjectionApplication
+
+fun main(args: Array<String>) {
+    SpringApplication.run(KotlinValueInjectionApplication::class.java, *args)
+}

spring-boot-kotlin/src/main/kotlin/com/baeldung/theValueAnnotation/ValueBean.kt

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+package com.baeldung.theValueAnnotation
+
+import org.springframework.beans.factory.annotation.Value
+import org.springframework.stereotype.Component
+
+@Component
+class ValueBean(
+    // without default values
+    @Value("\${my-app.magic-number}")
+    val magicNumber: Int,
+    @Value("\${my-app.magic-string}")
+    val magicString: String,
+    @Value("\${my-app.magic-flag}")
+    val magicFlag: Boolean,
+
+    // with default values
+    @Value("\${my-app.not-defined-value:1024}")
+    val magicNumberWithDefault: Int,
+    @Value("\${my-app.magic-string-with-default:default Value}")
+    val magicStringWithDefault: String,
+
+    // with null as the default value
+    @Value("\${my-app.not-defined-value:null}")
+    val stringDefaultLiteralNull: String?,
+    @Value("\${my-app.not-defined-value:#{null}}")
+    val stringDefaultNull: String?
+)

spring-boot-kotlin/src/main/kotlin/com/baeldung/theValueAnnotation/YamlPropertySourceFactory.kt

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+package com.baeldung.theValueAnnotation
+
+import org.springframework.beans.factory.config.YamlPropertiesFactoryBean
+import org.springframework.core.env.PropertiesPropertySource
+import org.springframework.core.env.PropertySource
+import org.springframework.core.io.support.EncodedResource
+import org.springframework.core.io.support.PropertySourceFactory
+import org.springframework.lang.Nullable
+
+class YamlPropertySourceFactory : PropertySourceFactory {
+    override fun createPropertySource(@Nullable name: String?, encodedResource: EncodedResource): PropertySource<*> =
+        PropertiesPropertySource(
+            encodedResource.resource.filename,
+            (YamlPropertiesFactoryBean().also { it.setResources(encodedResource.resource) }.getObject())
+        )
+}

spring-boot-kotlin/src/main/resources/application-inject-value.yml

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+my-app:
+  magic-number: 42
+  magic-string: "It's a magic string"
+  magic-flag: true
+
+  magic-string-with-default: "It's another magic string"

spring-boot-kotlin/src/test/kotlin/com/baeldung/theValueAnnotation/TheValueAnnotationUnitTest.kt

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+package com.baeldung.theValueAnnotation
+
+import org.junit.jupiter.api.Test
+import org.springframework.boot.test.context.SpringBootTest
+import org.springframework.test.context.TestConstructor
+import org.springframework.test.context.TestConstructor.AutowireMode
+import kotlin.test.assertEquals
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+@SpringBootTest
+@TestConstructor(autowireMode = AutowireMode.ALL)
+class TheValueAnnotationUnitTest(val valueBean: ValueBean) {
+
+    @Test
+    fun `when using value annotations, then expected values should be injected`() {
+        with(valueBean) {
+            assertEquals(42, magicNumber)
+            assertEquals("It's a magic string", magicString)
+            assertTrue(magicFlag)
+        }
+    }
+
+    @Test
+    fun `when using value annotations with default values, then expected values should be injected`() {
+        with(valueBean) {
+            assertEquals(1024, magicNumberWithDefault)
+            assertEquals("It's another magic string", magicStringWithDefault)
+        }
+    }
+
+    @Test
+    fun `when using value annotations with null as default values, then expected values should be injected`() {
+        with(valueBean) {
+            assertEquals("null", stringDefaultLiteralNull)
+            assertNull(stringDefaultNull)
+        }
+    }
+}