带有闭包和空安全检查的Groovy集合排序导致异常

我的代码中有如下语句：

otherParents.sort{-it.parent.lastUpdateDate.time}.each{
// ...
}

有时，

lastUpdateDate

将为空，并导致异常

我是groovy的新手，我尝试过问号之类的东西

otherParents.sort { -it.parent?.lastUpdateDate?.time }.each {
// ...
}

---

但是这也不起作用

有两种方法可以解决这个问题。如果要保留带有

null

date的条目，则必须传递表示比较器的闭包，如下所示：

otherParents.sort { a,b -> b.parent.lastUpdatedDate?.time <=> a.parent.lastUpdatedDate?.time }.each {
    println it
}

唯一的区别是，第二个示例将只对具有非null last Update的条目列表进行排序

在下面，您可以找到一个示例及其产生的输出：

import java.text.SimpleDateFormat

def date = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss")

def otherParents = [
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:00")]],
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:01")]],
        [parent: [lastUpdatedDate: null]],
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:02")]],
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:03")]],
        [parent: [lastUpdatedDate: null]],
        [parent: [lastUpdatedDate: null]]
]

otherParents.sort { a,b -> b.parent.lastUpdatedDate?.time <=> a.parent.lastUpdatedDate?.time }.each {
    println it
}

println "----"

otherParents.findAll { it.parent.lastUpdatedDate != null }.sort { -it.parent.lastUpdatedDate.time }.each {
    println it
}

---

你确定在添加后？。运算符由于lastUpdateTime为null而失败。也可能是其他原因。是的，在这种情况下失败，因为

negative（）

函数不能应用于

null

值。@SomBhattacharyya，是的，错误消息是相同的。

import java.text.SimpleDateFormat

def date = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss")

def otherParents = [
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:00")]],
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:01")]],
        [parent: [lastUpdatedDate: null]],
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:02")]],
        [parent: [lastUpdatedDate: date.parse("2018-10-26T10:00:03")]],
        [parent: [lastUpdatedDate: null]],
        [parent: [lastUpdatedDate: null]]
]

otherParents.sort { a,b -> b.parent.lastUpdatedDate?.time <=> a.parent.lastUpdatedDate?.time }.each {
    println it
}

println "----"

otherParents.findAll { it.parent.lastUpdatedDate != null }.sort { -it.parent.lastUpdatedDate.time }.each {
    println it
}

[parent:[lastUpdatedDate:Fri Oct 26 10:00:03 CEST 2018]]
[parent:[lastUpdatedDate:Fri Oct 26 10:00:02 CEST 2018]]
[parent:[lastUpdatedDate:Fri Oct 26 10:00:01 CEST 2018]]
[parent:[lastUpdatedDate:Fri Oct 26 10:00:00 CEST 2018]]
[parent:[lastUpdatedDate:null]]
[parent:[lastUpdatedDate:null]]
[parent:[lastUpdatedDate:null]]
----
[parent:[lastUpdatedDate:Fri Oct 26 10:00:03 CEST 2018]]
[parent:[lastUpdatedDate:Fri Oct 26 10:00:02 CEST 2018]]
[parent:[lastUpdatedDate:Fri Oct 26 10:00:01 CEST 2018]]
[parent:[lastUpdatedDate:Fri Oct 26 10:00:00 CEST 2018]]