BAEL-1838 (#4692)

* #BAEL-1838 code samples. Renamed LambdaKotlinTest to have the build succeed.

* #BAEL-1838 code samples w/inheritance.

* #BAEL-1838 renamed logger helper function to getLogger to avoid confusion.

* #BAEL-1838 renamed logger helper function to getLogger to avoid confusion.

core-kotlin/pom.xml

@@ -60,7 +60,6 @@
             <groupId>org.jetbrains.kotlin</groupId>
             <artifactId>kotlin-reflect</artifactId>
             <version>${kotlin-reflect.version}</version>
-            <scope>test</scope>
         </dependency>
         <dependency>
             <groupId>org.jetbrains.kotlinx</groupId>
@@ -224,10 +223,11 @@
     </build>
 
     <properties>
-        <kotlin-maven-plugin.version>1.2.41</kotlin-maven-plugin.version>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <kotlin-test-junit.version>1.2.41</kotlin-test-junit.version>
+        <kotlin-maven-plugin.version>1.2.51</kotlin-maven-plugin.version>
-        <kotlin-stdlib.version>1.2.41</kotlin-stdlib.version>
+        <kotlin-test-junit.version>1.2.51</kotlin-test-junit.version>
-        <kotlin-reflect.version>1.2.41</kotlin-reflect.version>
+        <kotlin-stdlib.version>1.2.51</kotlin-stdlib.version>
+        <kotlin-reflect.version>1.2.51</kotlin-reflect.version>
         <kotlinx.version>0.22.5</kotlinx.version>
         <ktor.io.version>0.9.2</ktor.io.version>
         <mockito-kotlin.version>1.5.0</mockito-kotlin.version>

core-kotlin/src/main/kotlin/com/baeldung/kotlin/logging/LoggerAsExtensionOnAny.kt

@@ -0,0 +1,30 @@
+package com.baeldung.kotlin.logging
+
+import org.slf4j.Logger
+
+open class LoggerAsExtensionOnAny {
+    val logger = logger()
+
+    fun log(s: String) {
+        logger().info(s)
+        logger.info(s)
+    }
+}
+
+class ExtensionSubclass : LoggerAsExtensionOnAny()
+
+fun <T : Any> T.logger(): Logger = getLogger(getClassForLogging(javaClass))
+
+fun main(args: Array<String>) {
+    LoggerAsExtensionOnAny().log("test")
+    ExtensionSubclass().log("sub")
+    "foo".logger().info("foo")
+    1.logger().info("uh-oh!")
+    SomeOtherClass().logger()
+}
+
+class SomeOtherClass {
+    fun logger(): String {
+        return "foo"
+    }
+}

core-kotlin/src/main/kotlin/com/baeldung/kotlin/logging/LoggerAsExtensionOnMarkerInterface.kt

@@ -0,0 +1,30 @@
+package com.baeldung.kotlin.logging
+
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+
+interface Logging
+
+inline fun <reified T : Logging> T.logger(): Logger =
+        //Wrong logger name!
+        //LoggerFactory.getLogger(javaClass.name + " w/interface")
+        LoggerFactory.getLogger(getClassForLogging(T::class.java).name + " w/interface")
+
+open class LoggerAsExtensionOnMarkerInterface : Logging {
+    companion object : Logging {
+        val logger = logger()
+    }
+
+    fun log(s: String) {
+        logger().info(s)
+        logger.info(s)
+    }
+}
+
+class MarkerExtensionSubclass : LoggerAsExtensionOnMarkerInterface()
+
+fun main(args: Array<String>) {
+    LoggerAsExtensionOnMarkerInterface().log("test")
+    MarkerExtensionSubclass().log("sub")
+    "foo".logger().info("foo")
+}

core-kotlin/src/main/kotlin/com/baeldung/kotlin/logging/LoggerAsProperty.kt

@@ -0,0 +1,17 @@
+package com.baeldung.kotlin.logging
+
+open class LoggerAsProperty {
+    private val logger = getLogger(javaClass)
+
+    fun log(s: String) {
+        logger.info(s)
+    }
+
+}
+
+class PropertySubclass : LoggerAsProperty()
+
+fun main(args: Array<String>) {
+    LoggerAsProperty().log("test")
+    PropertySubclass().log("sub")
+}

core-kotlin/src/main/kotlin/com/baeldung/kotlin/logging/LoggerAsPropertyDelegate.kt

@@ -0,0 +1,47 @@
+package com.baeldung.kotlin.logging
+
+import org.slf4j.Logger
+import kotlin.properties.ReadOnlyProperty
+import kotlin.reflect.KProperty
+
+open class LoggerAsPropertyDelegate {
+    private val lazyLogger by lazyLogger()
+    protected val logger by LoggerDelegate()
+    private val logger2 = logger
+
+    companion object {
+        private val lazyLoggerComp by lazyLogger()
+        private val loggerComp by LoggerDelegate()
+    }
+
+    open fun log(s: String) {
+        logger.info(s)
+        logger2.info(s)
+        lazyLogger.info(s)
+        loggerComp.info(s)
+        lazyLoggerComp.info(s)
+    }
+
+}
+
+class DelegateSubclass : LoggerAsPropertyDelegate() {
+    override fun log(s: String) {
+        logger.info("-- in sub")
+        super.log(s)
+    }
+}
+
+fun lazyLogger(forClass: Class<*>): Lazy<Logger> =
+        lazy { getLogger(getClassForLogging(forClass)) }
+
+fun <T : Any> T.lazyLogger(): Lazy<Logger> = lazyLogger(javaClass)
+
+fun main(args: Array<String>) {
+    LoggerAsPropertyDelegate().log("test")
+    DelegateSubclass().log("sub")
+}
+
+class LoggerDelegate<in R : Any> : ReadOnlyProperty<R, Logger> {
+    override fun getValue(thisRef: R, property: KProperty<*>) =
+        getLogger(getClassForLogging(thisRef.javaClass))
+}

core-kotlin/src/main/kotlin/com/baeldung/kotlin/logging/LoggerInCompanionObject.kt

@@ -0,0 +1,44 @@
+package com.baeldung.kotlin.logging
+
+open class LoggerInCompanionObject {
+    companion object {
+        private val loggerWithExplicitClass = getLogger(LoggerInCompanionObject::class.java)
+        @Suppress("JAVA_CLASS_ON_COMPANION")
+        private val loggerWithWrongClass = getLogger(javaClass)
+        @Suppress("JAVA_CLASS_ON_COMPANION")
+        private val logger = getLogger(javaClass.enclosingClass)
+    }
+
+    fun log(s: String) {
+        loggerWithExplicitClass.info(s)
+        loggerWithWrongClass.info(s)
+        logger.info(s)
+    }
+
+    class Inner {
+        companion object {
+            private val loggerWithExplicitClass = getLogger(Inner::class.java)
+            @Suppress("JAVA_CLASS_ON_COMPANION")
+            @JvmStatic
+            private val loggerWithWrongClass = getLogger(javaClass)
+            @Suppress("JAVA_CLASS_ON_COMPANION")
+            @JvmStatic
+            private val logger = getLogger(javaClass.enclosingClass)
+        }
+
+        fun log(s: String) {
+            loggerWithExplicitClass.info(s)
+            loggerWithWrongClass.info(s)
+            logger.info(s)
+        }
+    }
+
+}
+
+class CompanionSubclass : LoggerInCompanionObject()
+
+fun main(args: Array<String>) {
+    LoggerInCompanionObject().log("test")
+    LoggerInCompanionObject.Inner().log("test")
+    CompanionSubclass().log("sub")
+}

core-kotlin/src/main/kotlin/com/baeldung/kotlin/logging/Util.kt

@@ -0,0 +1,13 @@
+package com.baeldung.kotlin.logging
+
+import org.slf4j.Logger
+import org.slf4j.LoggerFactory
+import kotlin.reflect.full.companionObject
+
+fun getLogger(forClass: Class<*>): Logger = LoggerFactory.getLogger(forClass)
+
+fun <T : Any> getClassForLogging(javaClass: Class<T>): Class<*> {
+    return javaClass.enclosingClass?.takeIf {
+        it.kotlin.companionObject?.java == javaClass
+    } ?: javaClass
+}