Java based logger with auto tagging for Android apps. No need to use any log library.

Logger.kt

//region initializing the logger using the application object or any other way
class CoreApplication : Application() {
    private val initializer by inject<LogInitializer>()
    override fun onCreate() {
        super.onCreate()
        initializer.initialize()
    }
}

interface LogInitializer {
    fun initialize()
}
//endregion

//region logger initializer implementation exposed in the DI (hence the internal visibility)
internal class LogInitializerImpl(
    private val handler: Handler
) : LogInitializer {
    override fun initialize() {
        Logger.getLogger("").apply {
            level = Level.ALL
            handlers.forEach { removeHandler(it) }
            addHandler(handler)
        }
    }
}

internal class AndroidLogHandler : Handler() {

    private val Level.androidLevel: Int
        get() = when (intValue()) {
            Level.SEVERE.intValue() -> Log.ERROR
            Level.WARNING.intValue() -> Log.WARN
            Level.INFO.intValue() -> Log.INFO
            Level.FINE.intValue() -> Log.DEBUG
            else -> Log.DEBUG
        }

    override fun publish(record: LogRecord) {
        val tag = record.loggerName
        val message = record.thrown?.let { thrown ->
            "${record.message}: ${Log.getStackTraceString(thrown)}"
        } ?: record.message

        Log.println(record.level.androidLevel, tag, message)
    }

    override fun flush() {
        // no-op
    }

    override fun close() {
        // no-op
    }
}
//endregion

//region no-op logger initializer exposed in the DI (hence the internal visibility)
internal class NoOpLogInitializer : LogInitializer {
    override fun initialize() {
        // no-op
    }
}
//endregion

// region CoreLogger.kt
val Any.coreLogger: CoreLogger
    get() = InternalLogger(logger = Logger.getLogger(this@coreLogger::class.java.simpleName))

private class InternalLogger(
    private val logger: Logger,
) : CoreLogger {
    override fun d(message: String) {
        logger.log(Level.FINE, message)
    }

    override fun i(message: String) {
        logger.log(Level.INFO, message)
    }

    override fun w(message: String) {
        logger.log(Level.WARNING, message)
    }

    override fun e(message: String) {
        logger.log(Level.SEVERE, message)
    }

    override fun e(throwable: Throwable, message: String) {
        logger.log(Level.SEVERE, message, throwable)
    }
}

interface CoreLogger {
    fun d(message: String)
    fun i(message: String)
    fun w(message: String)
    fun e(message: String)
    fun e(throwable: Throwable, message: String)
}
//endregion