[英]Scala WindowFunction does not compile
我一直在使用Apache Flink編寫原型應用程序。 在此過程中,我選擇將org.apache.flink.streaming.api.functions.windowing.WindowFunction用於特定的用例。 但是,在編寫apply()函數的主體時,我遇到了此錯誤(以下代碼並非來自我正在編寫的應用程序-我的數據類型不同-它來自Flink文檔站點中的示例代碼):
import scala.collection.Iterable
import scala.collection.Map
import org.apache.flink.streaming.api.functions.windowing.WindowFunction
import org.apache.flink.streaming.api.windowing.windows.{TimeWindow}
import org.apache.flink.util.Collector
import scala.collection.JavaConversions._
class MyWindowFunction extends WindowFunction[(String, Long), String, String, TimeWindow] {
def apply(key: String, window: TimeWindow, input: Iterable[(String, Long)], out: Collector[String]): Unit = {
var count = 0L
for (in <- input) {
count = count + 1
}
out.collect(s"Window $window count: $count")
}
}
編譯器抱怨:
Error:(16, 7) class MyWindowFunction needs to be abstract, since method apply in trait WindowFunction of type
(x$1: String, x$2: org.apache.flink.streaming.api.windowing.windows.TimeWindow,
x$3: Iterable[(String, Long)],
x$4: org.apache.flink.util.Collector[String])Unit is not defined
class MyWindowFunction extends WindowFunction[(String, Long), String, String, TimeWindow] {
我已經檢查了apply()中參數的順序; 他們似乎是正確的。
由於某些原因,我無法找出錯誤的確切來源。 有人可以將我推向解決方案嗎?
我已找到此錯誤的原因。
我不清楚的是,Apache Flink的API需要一個java.lang.Iterable,而不是它的Scala等同物:
class MyWindowFunction extends
WindowFunction[(String, Long), String, String, TimeWindow] {
override
def apply(
key: String,
w: TimeWindow,
iterable: Iterable[(String, Long)], // from java.lang.Iterable
collector: Collector[String]): Unit = {
// ....
}
}
因此,我必須適當地導入:
import java.lang.Iterable // From Java
import java.util.Map // From Java
import org.apache.flink.streaming.api.functions.windowing.WindowFunction
import org.apache.flink.streaming.api.windowing.windows.TimeWindow
import org.apache.flink.util.Collector
import scala.collection.JavaConversions._ // Implicit conversions
class MyWindowFunction
extends WindowFunction[(String, Long), String, String, TimeWindow] {
override
def apply(
key: String,
w: TimeWindow,
iterable: Iterable[(String, Long)],
collector: Collector[String]): Unit = {
// ....
}
}
一切都好!
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