在Groovy中获取地图的方法

问题描述：

在Config.groovy中：

In Config.groovy:

Query {
    parameterMap {
        time.'1328' =  ['T1']
        time.'1329' =  ['T2']
        templates.'T1'   =  ['X','Y','Z']
        templates.'T2'   =  ['Z']
    }
}

在QuartzSchedulerJob I中想要使用 templateId 的 T1 和 T2 作为键在 parameterMap 中获取相应的值，但它返回 null 和 [：] ，分别为 parameterMap.templates.get（ $ {v}），但我想获取 ['X'，' T1 和Y'，'Z'] 和 ['Z'] T2

In QuartzSchedulerJob I want to use T1 and T2 which are templateId as key to get the corresponding values in parameterMap but it returns me null and [:] respectively, parameterMap.templates.get("${v}") but I want to get ['X','Y','Z'] and ['Z'] respectively for T1 and T2

def execute() {
    def currentTime = new Date().format('HHmm')
    grailsApplication.config.Query.parameterMap.time.each { k, v ->
        if (currentTime=="${k}") {
            println "${k} " + currentTime
            String templateId = "${v}".replaceAll("\\[", "").replaceAll("\\]","")
            println grailsApplication.config.Query.parameterMap.templates.get("${v}") //this prints null
            println grailsApplication.config.Query.parameterMap.templates.getAt("${v}") //this prints [:]
        }
    }
}

答

$ {k} 是一个怪异的表达式，在Groovy代码中我经常看到它。我很想知道是谁和/或什么（书/博客/ ???）使人们使用了这种语法。我经常在打算返回类字段作为值的 toString 方法中看到它，例如

"${k}" is a weird expression, and I see it a lot in Groovy code. I would love to know who and/or what (book/blog/???) somehow got people using that syntax. I see it quite often in toString methods that intend to return a class field as the value, e.g.

private String name
...
String toString() {
   "${name}"
}

为什么不只返回变量？

String toString() {
   name
}

您正在执行此操作在这里，制作一个 GString $ {k} 仅包含一个嵌入式变量，而没有其他字符，然后在将它与 currentTime （可以工作，但远非最佳或明智的方法）进行比较并使用此 GString $ c时，将其隐式转换为String $ c>在调用 get 和 Map 中的潜在键code> getAt ，想知道为什么这个奇怪的小 GString 中的值非常接近作为地图键（例如Tim指出时间地图的值是单元素 List s，而 templates 映射的键是 String 这些 List s中的单个元素code> s也不会自动转换成您想要的样子。

You're doing this here, making a GString "${k}" with only a single embedded variable and no other characters, and then implicitly converting it to a String when comparing it to currentTime (which works, but is far from optimal or sensible) and using this GString to generate (in a very funky way) to a potential key in a Map when calling get and getAt, and wondering why the value inside this weird little GString, which is very close to being a map key (as Tim points out the values of the time map are single-element Lists, and the keys of the templates map are Strings which are the single elements of these Lists) isn't also automagically converted into what you wanted it to have been.

Groovy进行了大量隐式转换，但是 Map 中 get 方法的签名>是 Object get（Object key）（从技术上讲，它有一个通用的返回类型，但这在这里不相关），因此Groovy不会为您做任何转换-您将 Object 作为参数传递给采用 Object 的方法。完全没有理由期望它会被转换为String，或者转换为任何键的任何类型，或者转换为任何东西。

Groovy does lots of implicit conversions, but the signature of the get method in Map is Object get(Object key) (technically it's got a generic return type, but that's not relevant here) so Groovy isn't going to do any conversion for you - you're passing an Object as a parameter to a method that takes Object. There's no reason at all to expect that it would be converted to a String, or to any of the types of any of the keys, or to anything at all.

loc伤害了我的大脑：

This loc hurts my brain:

String templateId = "${v}".replaceAll("\\[", "").replaceAll("\\]","")

您正在列出 v ，将其与其他内容一起嵌入 GString ，强制Groovy将 GString 转换为 String ，以便它可以调用 replaceAll ，以删除 AbstractCollection toString 形式的开头和结尾的方括号/ code>，以提取 v 中的单个 String 元素。

You're taking the list v, converting it to a String by embedding it with nothing else in a GString, coercing Groovy to convert the GString to a String so it can call replaceAll on it, to remove the brackets that are at the beginning and end of the toString form of AbstractCollection, to extract the single String element in v.

如何更直接一些：

String templateId = v[0]

及其在清理后的 execute 版本中的使用：

and its use in a cleaned up version of execute:

def execute() {
    String currentTime = new Date().format('HHmm')
    grailsApplication.config.Query.parameterMap.time.each { k, v ->
        if (currentTime == k) {
            println "$k $currentTime"
            String templateId = v[0]
            println config.Query.parameterMap.templates[templateId] // get and getAt would also work
        }
    }
}

在Groovy中获取地图的方法

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