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我正在尝试以惯用方式转换 Kotlin 中称为责任链的设计模式的 Java 代码。但是我对appendNext()在 Kotlin 中转换 Java 接口的默认方法没有任何线索。我尝试了一些已经存在的问题，例如this和this，但它们似乎不适用于我的用例。

我尝试将默认方法转换为appendNext()Kotlin 中的扩展函数。但显然 Kotlin 似乎没有找到方法Logger.message()并 throws NoSuchMethodError。

我在以下片段中给出了迄今为止我尝试过的原始 Java 代码和 Kotlin 代码。

我更喜欢此代码的 Kotlin 惯用解决方案，而不使用@JvmDefault注释。代码应该和 Java 一样简洁。任何帮助将非常感激。

Java 代码

这是设计模式责任链的正确工作 Java 代码：

import java.util.Arrays;
import java.util.EnumSet;
import java.util.function.Consumer;

@FunctionalInterface
public interface Logger {
    public enum LogLevel {
        INFO, DEBUG, WARNING, ERROR, FUNCTIONAL_MESSAGE, FUNCTIONAL_ERROR;

        public static LogLevel[] all() {
            return values();
        }
    }

    abstract void message(String msg, LogLevel severity);

    default Logger appendNext(Logger nextLogger) {
        return (msg, severity) -> {
            message(msg, severity);
            nextLogger.message(msg, severity);
        };
    }

    static Logger writeLogger(LogLevel[] levels, Consumer<String> stringConsumer) {
        EnumSet<LogLevel> set = EnumSet.copyOf(Arrays.asList(levels));
        return (msg, severity) -> {
            if (set.contains(severity)) {
                stringConsumer.accept(msg);
            }
        };
    }

    static Logger consoleLogger(LogLevel... levels) {
        return writeLogger(levels, msg -> System.err.println("Writing to console: " + msg));
    }

    static Logger emailLogger(LogLevel... levels) {
        return writeLogger(levels, msg -> System.err.println("Sending via email: " + msg));
    }

    static Logger fileLogger(LogLevel... levels) {
        return writeLogger(levels, msg -> System.err.println("Writing to Log File: " + msg));
    }

    public static void main(String[] args) {
        // Build an immutable chain of responsibility
        Logger logger = consoleLogger(LogLevel.all())
                .appendNext(emailLogger(LogLevel.FUNCTIONAL_MESSAGE, LogLevel.FUNCTIONAL_ERROR))
                .appendNext(fileLogger(LogLevel.WARNING, LogLevel.ERROR));

        // Handled by consoleLogger since the console has a LogLevel of all
        logger.message("Entering function ProcessOrder().", LogLevel.DEBUG);
        logger.message("Order record retrieved.", LogLevel.INFO);

        // Handled by consoleLogger and emailLogger since emailLogger implements Functional_Error & Functional_Message
        logger.message("Unable to Process Order ORD1 Dated D1 For Customer C1.", LogLevel.FUNCTIONAL_ERROR);
        logger.message("Order Dispatched.", LogLevel.FUNCTIONAL_MESSAGE);

        // Handled by consoleLogger and fileLogger since fileLogger implements Warning & Error
        logger.message("Customer Address details missing in Branch DataBase.", LogLevel.WARNING);
        logger.message("Customer Address details missing in Organization DataBase.", LogLevel.ERROR);
    }
}

科特林代码

这是我到目前为止所尝试的。我将其Enum移至一个单独的文件并将所有内容都保留在顶层。看看appendNext()方法，这似乎是问题的原因。

记录器.kt

import java.util.*
import java.util.function.Consumer

interface Logger {
    fun message(message: String, severity: LogLevel)
}

fun Logger.appendNext(nextLogger: Logger): Logger {
    return object: Logger {
        override fun message(message: String, severity: LogLevel) {
            message(message, severity)
            nextLogger.message(message, severity)
        }
    }
}

fun writeLogger(
    stringConsumer: Consumer<String>,
    vararg levels: LogLevel
): Logger {
    val set = EnumSet.copyOf(listOf(*levels))
    return object: Logger {
        override fun message(message: String, severity: LogLevel) {
            if (set.contains(severity)) {
                stringConsumer.accept(message)
            }
        }
    }
}

fun consoleLogger(vararg levels: LogLevel): Logger {
    return writeLogger(
        Consumer { msg: String -> System.err.println("Writing to console: $msg") },
        *levels
    )
}

fun emailLogger(vararg levels: LogLevel): Logger {
    return writeLogger(
        Consumer { msg: String -> System.err.println("Sending via email: $msg") },
        *levels
    )
}

fun fileLogger(vararg levels: LogLevel): Logger {
    return writeLogger(
        Consumer { msg: String -> System.err.println("Writing to Log File: $msg") },
        *levels
    )
}

fun main() {
    // Build an immutable chain of responsibility
    val logger = consoleLogger(*LogLevel.all())
        .appendNext(emailLogger(LogLevel.FUNCTIONAL_MESSAGE, LogLevel.FUNCTIONAL_ERROR))
        .appendNext(fileLogger(LogLevel.WARNING, LogLevel.ERROR))

    // Handled by consoleLogger since the console has a LogLevel of all
    logger.message("Entering function ProcessOrder().", LogLevel.DEBUG)
    logger.message("Order record retrieved.", LogLevel.INFO)

    // Handled by consoleLogger and emailLogger since emailLogger implements Functional_Error & Functional_Message
    logger.message("Unable to Process Order ORD1 Dated D1 For Customer C1.", LogLevel.FUNCTIONAL_ERROR)
    logger.message("Order Dispatched.", LogLevel.FUNCTIONAL_MESSAGE)

    // Handled by consoleLogger and fileLogger since fileLogger implements Warning & Error
    logger.message("Customer Address details missing in Branch DataBase.", LogLevel.WARNING)
    logger.message("Customer Address details missing in Organization DataBase.", LogLevel.ERROR)
}

日志级别.kt

enum class LogLevel {
    INFO, DEBUG, WARNING, ERROR, FUNCTIONAL_MESSAGE, FUNCTIONAL_ERROR;

    companion object {
        public fun all(): Array<LogLevel> {
            return values()
        }
    }
}
4

2 回答 2

1

我不明白您为什么要添加currentLogger原始 Java 代码中不存在的属性。

如果您想要与 Java 中相同的行为，其中一个实现可以覆盖 的默认实现appendNext()，它看起来像这样：

fun interface Logger {
    fun message(message: String, severity: LogLevel)

    fun appendNext(nextLogger: Logger): Logger {
        return Logger { message, severity ->
            message(message, severity)
            nextLogger.message(message, severity)
        }
    }
}

如果您不打算覆盖此函数，则将其移至扩展函数会更合适。然后“覆盖”它需要编写另一个具有相同签名的扩展函数并导入该函数来使用它。这就是标准库函数的组织方式。仍然不是万无一失的，但是将函数放在接口中会更强烈地表明它应该被覆盖。

fun interface Logger {
    fun message(message: String, severity: LogLevel)
}

fun Logger.appendNext(nextLogger: Logger): Logger {
    return Logger { message, severity ->
        message(message, severity)
        nextLogger.message(message, severity)
    }
}

编辑：另外，您不需要使用 Consumer，因为在 Kotlin 中函数是一流的类型。例如，替换Consumer<String>为(String) -> Unit，然后直接使用stringConsumer(message)而不是调用它stringConsumer.accept(message)。

于 2020-10-20T14:00:08.063 回答
1

此处最佳解决方案的关键是函数式接口的使用（在 Kotlin 1.4 中引入）

此外，为了使代码更简洁和惯用，请考虑使用单表达式函数，删除可以推断的类型，并重写EnumSet.copyOf(listOf(*levels))为辅助函数而无需创建额外的对象：

import java.util.*
import java.util.function.Consumer

fun interface Logger {
    fun message(msg: String, severity: LogLevel)
}

fun Logger.appendNext(nextLogger: Logger) = Logger { msg, severity ->
    message(msg, severity)
    nextLogger.message(msg, severity)
}

inline fun <reified E : Enum<E>> enumSetOf(e: Array<out E>): EnumSet<E> =
    EnumSet.noneOf(E::class.java).also { result -> e.forEach { result.add(it) } }

fun writeLogger(levels: Array<out LogLevel>, stringConsumer: Consumer<String>) = Logger { msg, severity ->
    if (severity in enumSetOf(levels)) {
        stringConsumer.accept(msg)
    }
}

fun consoleLogger(vararg levels: LogLevel) =
    writeLogger(levels) { msg -> System.err.println("Writing to console: $msg") }

fun emailLogger(vararg levels: LogLevel) =
    writeLogger(levels) { msg -> System.err.println("Sending via email: $msg") }

fun fileLogger(vararg levels: LogLevel) =
    writeLogger(levels) { msg -> System.err.println("Writing to Log File: $msg") }

fun main() {
    // Build an immutable chain of responsibility
    val logger = consoleLogger(*LogLevel.all())
        .appendNext(emailLogger(LogLevel.FUNCTIONAL_MESSAGE, LogLevel.FUNCTIONAL_ERROR))
        .appendNext(fileLogger(LogLevel.WARNING, LogLevel.ERROR))

    // Handled by consoleLogger since the console has a LogLevel of all
    logger.message("Entering function ProcessOrder().", LogLevel.DEBUG)
    logger.message("Order record retrieved.", LogLevel.INFO)

    // Handled by consoleLogger and emailLogger since emailLogger implements Functional_Error & Functional_Message
    logger.message("Unable to Process Order ORD1 Dated D1 For Customer C1.", LogLevel.FUNCTIONAL_ERROR)
    logger.message("Order Dispatched.", LogLevel.FUNCTIONAL_MESSAGE)

    // Handled by consoleLogger and fileLogger since fileLogger implements Warning & Error
    logger.message("Customer Address details missing in Branch DataBase.", LogLevel.WARNING)
    logger.message("Customer Address details missing in Organization DataBase.", LogLevel.ERROR)
}
于 2020-10-20T14:56:38.087 回答