使用条件日志关闭 [英] Closure with conditional logging

问题描述

我有这样的功能：

private downloadAllFiles() {
    sftpRetriever.listFiles().findAll {
        filter.isResponse(it) || filter.isResponseTurned(it)
    }.each { String fileName ->
        log.info 'Downloading file: {}', fileName
        sftpRetriever.downloadFile(fileName)
        log.info 'File downloaded'
        removeRemoteFile(fileName)
    }
}

我正在寻找一个简单的方法来修改这个闭包里面的函数如果findAll的size（）是0，它将只记录没有更多的文件要下载和.each将不会被执行。有没有任何简单的方法来使它在单闭合？如果我把它分成几个部分，但试图在这里学习闭包并提高我的表达力，这真的是简单的任务:)提前为您的帮助。

I am looking for a simple way of modyfing this closure inside of that function so if the size() of findAll is 0 it will simply log 'No more files to download' and .each won't be executed. Is there any simple way to make it in single closure? It is really simply task if I divide it in several parts, but trying to learn closures here and improve my expressiveness :) Thank you in advance for your help.

推荐答案

看看下面的生物:)它的工作原因是 each 返回调用它的集合（+ elvis操作符和相当不错的Groovy的真理评估）：

Take a look at creature below :) It works due the fact that each returns the collection on which it's invoked (+ elvis operator and quite nice Groovy's truth evaluation):

def printContents(Collection collection) {
    collection.each {
        println it
    } ?: println('Collection is empty')
}

printContents([1,2,'hello'])
printContents([])

您也可以使用元编程添加由Steinar提供的方法。在首次使用之前必须将其添加到 metaClass ，但是您将避免尝试创建扩展模块：

You can also use metaprogramming to add the method provided by Steinar. It must be added to metaClass before first use but you'll avoid an effort to make extension module:

Collection.metaClass.doIfEmpty { Closure ifEmptyClosure ->
        if (delegate.empty) {
            ifEmptyClosure()
        }
        return delegate
}

def printContents(Collection collection) {
    collection.doIfEmpty {
        println "Collection is empty"
    }.each {
        println it
    }
}

printContents([1,2,'hello'])
printContents([])

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