groovy:安全地在地图中找到一个键并返回其值 [英] groovy: safely find a key in a map and return its value

问题描述

我想在给定的地图中找到特定的钥匙.如果找到了密钥，那么我想从地图上获取该密钥的值.

I want to find a specific key in a given map. If the key is found, I then want to get the value of that key from the map.

这是我到目前为止所管理的:

This is what I managed so far:

def mymap = [name:"Gromit", likes:"cheese", id:1234]

def x = mymap.find{ it.key == "likes" }

if(x)
    println x.value

此方法有效，输出为预期的奶酪".很好，但是我不想最后做x.value，也不想做if(x).我希望x以某种方式直接包含该值.

This works, the output is "cheese" as expected. Great, but I don't want to do x.value at the end, and I don't want to do if(x). I want x to directly contain the value somehow.

我不能像这样直接将值获取到x中:

I can't get the value directly into x like this:

def mymap = [name:"Gromit", likes:"cheese", id:1234]

def x = mymap.find{ it.key == "likesZZZ" }.value

println x

由于在这种情况下find闭包为null，因此将导致Null Pointer Exception.当然，上面的代码片段在it.key == "likes"时有效，但是我不确定是否总是会在地图上找到目标键.

Because the find closure is null in this case, this results in a Null Pointer Exception. Of course, the above code snippet works when it.key == "likes", but I am not sure that I will always find the target key in the map.

在地图上执行此操作的"Groovier"是安全的方法:

What is a "Groovier" and safe way to do this on a map:

• 检查地图是否具有给定的键，
• 如果是这样，获取此键的值

推荐答案

def mymap = [name:"Gromit", id:1234]
def x = mymap.find{ it.key == "likes" }?.value
if(x)
    println "x value: ${x}"

println x.getClass().name

?.检查是否为空，并且不会在Groovy中创建异常.如果密钥不存在，则结果为org.codehaus.groovy.runtime.NullObject.

?. checks for null and does not create an exception in Groovy. If the key does not exist, the result will be a org.codehaus.groovy.runtime.NullObject.

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