Kotlin 没有与 Java 中使用的静态字段相同的概念。在 Java 中，普遍接受的日志记录方式是:

public class Foo {
    private static final Logger LOG = LoggerFactory.getLogger(Foo.class);
}

最佳答案

在大多数成熟的 Kotlin 代码中，您会在下面找到其中一种模式。使用 的方法属性(property)代表利用 Kotlin 的强大功能来生成最小的代码。

注意:这里的代码适用于 java.util.Logging但同样的理论适用于任何日志库

类静电 (常见的，相当于问题中的 Java 代码)

如果您不能相信日志系统内的哈希查找的性能，您可以通过使用一个伴随对象获得与您的 Java 代码类似的行为，该对象可以保存一个实例并让您感觉像是静态的。

class MyClass {
    companion object {
        val LOG = Logger.getLogger(MyClass::class.java.name) 
    }

    fun foo() {
        LOG.warning("Hello from MyClass")
    }
}  

Dec 26, 2015 11:28:32 AM org.stackoverflow.kotlin.test.MyClass foo INFO: Hello from MyClass

class MyClass {
  val LOG = Logger.getLogger(this.javaClass.name)

  fun foo() {
        LOG.warning("Hello from MyClass")
  }
} 

Dec 26, 2015 11:28:44 AM org.stackoverflow.kotlin.test.MyClass foo INFO: Hello from MyClass

fun <R : Any> R.logger(): Lazy<Logger> {
    return lazy { Logger.getLogger(unwrapCompanionClass(this.javaClass).name) }
}
// see code for unwrapCompanionClass() below in "Putting it all Together section"

class Something {
    val LOG by logger()

    fun foo() {
        LOG.info("Hello from Something")
    }
}

class SomethingElse {
    companion object {
        val LOG by logger()

    }

    fun foo() {
        LOG.info("Hello from SomethingElse")
    }
}

Dec 26, 2015 11:30:55 AM org.stackoverflow.kotlin.test.Something foo INFO: Hello from Something

Dec 26, 2015 11:30:55 AM org.stackoverflow.kotlin.test.SomethingElse foo INFO: Hello from SomethingElse

// extend any class with the ability to get a logger
fun <T: Any> T.logger(): Logger {
     return Logger.getLogger(unwrapCompanionClass(this.javaClass).name)
}

class SomethingDifferent {
    val LOG = logger()

    fun foo() {
        LOG.info("Hello from SomethingDifferent")
    }
}

Dec 26, 2015 11:29:12 AM org.stackoverflow.kotlin.test.SomethingDifferent foo INFO: Hello from SomethingDifferent

val LOG1 = "".logger()
val LOG2 = Date().logger()
val LOG3 = 123.logger()

interface Loggable {} 

fun Loggable.logger(): Logger {
     return Logger.getLogger(unwrapCompanionClass(this.javaClass).name)
}    

interface Loggable {
    public fun logger(): Logger {
        return Logger.getLogger(unwrapCompanionClass(this.javaClass).name)
    }
}

class MarkedClass: Loggable {
    val LOG = logger()
}

Dec 26, 2015 11:41:01 AM org.stackoverflow.kotlin.test.MarkedClass foo INFO: Hello from MarkedClass

interface Loggable {
    val LOG: Logger  // abstract required field

    public fun logger(): Logger {
        return Logger.getLogger(unwrapCompanionClass(this.javaClass).name)
    }
}

class MarkedClass: Loggable {
    override val LOG: Logger = logger()
}

abstract class WithLogging: Loggable {
    override val LOG: Logger = logger()
}

// using the logging from the base class
class MyClass1: WithLogging() {
    // ... already has logging!
}

// providing own logging compatible with marker interface
class MyClass2: ImportantBaseClass(), Loggable {
    // ... has logging that we can understand, but doesn't change my hierarchy
    override val LOG: Logger = logger()
}

// providing logging from the base class via a companion object so our class hierarchy is not affected
class MyClass3: ImportantBaseClass() {
    companion object : WithLogging() {
       // we have the LOG property now!
    }
}

// Return logger for Java class, if companion object fix the name
fun <T: Any> logger(forClass: Class<T>): Logger {
    return Logger.getLogger(unwrapCompanionClass(forClass).name)
}

// unwrap companion class to enclosing class given a Java Class
fun <T : Any> unwrapCompanionClass(ofClass: Class<T>): Class<*> { 
   return ofClass.enclosingClass?.takeIf { 
      ofClass.enclosingClass.kotlin.companionObject?.java == ofClass 
   } ?: ofClass 
}

// unwrap companion class to enclosing class given a Kotlin Class
fun <T: Any> unwrapCompanionClass(ofClass: KClass<T>): KClass<*> {
   return unwrapCompanionClass(ofClass.java).kotlin
}

// Return logger for Kotlin class
fun <T: Any> logger(forClass: KClass<T>): Logger {
    return logger(forClass.java)
}

// return logger from extended class (or the enclosing class)
fun <T: Any> T.logger(): Logger {
    return logger(this.javaClass)
}

// return a lazy logger property delegate for enclosing class
fun <R : Any> R.lazyLogger(): Lazy<Logger> {
    return lazy { logger(this.javaClass) }
}

// return a logger property delegate for enclosing class
fun <R : Any> R.injectLogger(): Lazy<Logger> {
    return lazyOf(logger(this.javaClass))
}

// marker interface and related extension (remove extension for Any.logger() in favour of this)
interface Loggable {}
fun Loggable.logger(): Logger = logger(this.javaClass)

// abstract base class to provide logging, intended for companion objects more than classes but works for either
abstract class WithLogging: Loggable {
    val LOG = logger()
}

class MixedBagOfTricks {
    companion object {
        val LOG1 by lazyLogger()          // lazy delegate, 1 instance per class
        val LOG2 by injectLogger()        // immediate, 1 instance per class
        val LOG3 = logger()               // immediate, 1 instance per class
        val LOG4 = logger(this.javaClass) // immediate, 1 instance per class
    }

    val LOG5 by lazyLogger()              // lazy delegate, 1 per instance of class
    val LOG6 by injectLogger()            // immediate, 1 per instance of class
    val LOG7 = logger()                   // immediate, 1 per instance of class
    val LOG8 = logger(this.javaClass)     // immediate, 1 instance per class
}

val LOG9 = logger(MixedBagOfTricks::class)  // top level variable in package

// or alternative for marker interface in class
class MixedBagOfTricks : Loggable {
    val LOG10 = logger()
}

// or alternative for marker interface in companion object of class
class MixedBagOfTricks {
    companion object : Loggable {
        val LOG11 = logger()
    }
}

// or alternative for abstract base class for companion object of class
class MixedBagOfTricks {
    companion object: WithLogging() {} // instance 12

    fun foo() {
       LOG.info("Hello from MixedBagOfTricks")
    }
}

// or alternative for abstract base class for our actual class
class MixedBagOfTricks : WithLogging() { // instance 13
    fun foo() {
       LOG.info("Hello from MixedBagOfTricks")
    }
}

Dec 26, 2015 11:39:00 AM org.stackoverflow.kotlin.test.MixedBagOfTricks foo INFO: Hello from MixedBagOfTricks

关于kotlin - Kotlin 中的惯用登录方式，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/34416869/