Question

我正在尝试在Flink的DataStream上应用每个窗口功能。以下是我的代码

DataStream<Tuple2<String, String>> data = ...
DataStream<Tuple2<String, String>> freqCityChangeTransactions = data
    .keyBy(0)
    .timeWindow(Time.seconds(5))
    .process(new MyProcessWindowFunction());

以下是我对MyProcessWindowFunction的实现

public static class MyProcessWindowFunction
extends ProcessWindowFunction<Tuple2<String, String>, Tuple2<String, String>, String, TimeWindow> {

public void process(String key,
            Context context,
            Iterable<Tuple2<String, String>> input,
            Collector<Tuple2<String, String>> out) {
        // Do something ...
    }
}

但是，当我尝试通过maven编译以上代码时，出现以下错误

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.6.1:compile (default-compile) on project flink-examples: Compilation failure
[ERROR] /Users/furqan/Workspace/flink/src/main/java/com/baig/bank/Bank.java:[120,13] no suitable method found for process(com.baig.Bank.MyProcessWindowFunction)
[ERROR] method org.apache.flink.streaming.api.datastream.WindowedStream.<R>process(org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction<org.apache.flink.api.java.tuple.Tuple2<java.lang.String,java.lang.String>,R,org.apache.flink.api.java.tuple.Tuple,org.apache.flink.streaming.api.windowing.windows.TimeWindow>) is not applicable
[ERROR] (cannot infer type-variable(s) R
[ERROR] (argument mismatch; com.baig.Bank.MyProcessWindowFunction cannot be converted to org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction<org.apache.flink.api.java.tuple.Tuple2<java.lang.String,java.lang.String>,R,org.apache.flink.api.java.tuple.Tuple,org.apache.flink.streaming.api.windowing.windows.TimeWindow>))
[ERROR] method org.apache.flink.streaming.api.datastream.WindowedStream.<R>process(org.apache.flink.streaming.api.functions.windowing.ProcessWindowFunction<org.apache.flink.api.java.tuple.Tuple2<java.lang.String,java.lang.String>,R,org.apache.flink.api.java.tuple.Tuple,org.apache.flink.streaming.api.windowing.windows.TimeWindow>,org.apache.flink.api.common.typeinfo.TypeInformation<R>) is not applicable
[ERROR] (cannot infer type-variable(s) R
[ERROR] (actual and formal argument lists differ in length))

您知道我在这里做错什么吗？仅供参考，我正在使用Apache Flink 1.5.1版，并在Mac上使用maven3编译Java代码。

Answer 1

The problem is that there's a mismatch between the KeySelector used in the keyBy and the key type specified in the ProcessWindowFunction. You have specified the key using an index into the Tuple2, and as a consequence, the compiler is unable to infer that the keys will be Strings. In this situation, Flink passes the key as a Tuple.

There are a couple of ways you can fix this. If you leave the keyBy as is, then you'll need to modify the ProcessWindowFunction to use Tuple as the key type, and you'll have to cast the key to a String if you want to use it. Something like ((Tuple1<String>)key).f0. A better solution would be a use a more explicit key selector, such as keyBy(t -> t.f0), so that the keys are known to be Strings at compile time.

Flink：找不到适合的处理方法

1 个答案: