Flink InvalidTypesException: The return type of function could not be determined automatically...

初学Flink时遇到的小问题，后发现其实挺常见的，但还是稍作记录。

在WordCount的示例代码中有如下代码：

public static final class Tokenizer implements FlatMapFunction<String, Tuple2<String, Integer>> {@Overridepublic void flatMap(String value, Collector<Tuple2<String, Integer>> out) {// normalize and split the lineString[] tokens = value.toLowerCase().split("\\W+");// emit the pairsfor (String token : tokens) {if (token.length() > 0) {out.collect(new Tuple2<>(token, 1));}}}
}

发现它其实是一个函数式接口，想改写为Lambda表达式：

(String value, Collector<Tuple2<String, Integer>> out)->{// normalize and split the lineString[] tokens = value.toLowerCase().split("\\W+");// emit the pairsfor (String token : tokens) {if (token.length() > 0) {out.collect(new Tuple2<>(token, 1));}}}
)

报错：

Executing WordCount example with default input data set.
Use --input to specify file input.
Exception in thread "main" org.apache.flink.api.common.functions.InvalidTypesException: The return type of function 'main(WordCount.java:85)' could not be determined automatically, due to type erasure. You can give type information hints by using the returns(...) method on the result of the transformation call, or by letting your function implement the 'ResultTypeQueryable' interface.at org.apache.flink.api.java.DataSet.getType(DataSet.java:178)at org.apache.flink.api.java.DataSet.groupBy(DataSet.java:701)at org.apache.flink.examples.java.wordcount.WordCount.main(WordCount.java:98)
Caused by: org.apache.flink.api.common.functions.InvalidTypesException: The generic type parameters of 'Collector' are missing. In many cases lambda methods don't provide enough information for automatic type extraction when Java generics are involved. An easy workaround is to use an (anonymous) class instead that implements the 'org.apache.flink.api.common.functions.FlatMapFunction' interface. Otherwise the type has to be specified explicitly using type information.at org.apache.flink.api.java.typeutils.TypeExtractionUtils.validateLambdaType(TypeExtractionUtils.java:350)at org.apache.flink.api.java.typeutils.TypeExtractionUtils.extractTypeFromLambda(TypeExtractionUtils.java:176)at org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:571)at org.apache.flink.api.java.typeutils.TypeExtractor.getFlatMapReturnTypes(TypeExtractor.java:196)at org.apache.flink.api.java.DataSet.flatMap(DataSet.java:266)at org.apache.flink.examples.java.wordcount.WordCount.main(WordCount.java:85)

解决方法：

https://stackoverflow.com/questions/50945509/apache-flink-return-type-of-function-could-not-be-determined-automatically-due

.returns(Types.TUPLE(Types.STRING, Types.INT)) // 如果这里想用函数式接口的lambda表达式的话，需要明确泛型返回的类型

Flink InvalidTypesException: The return type of function could not be determined automatically...相关推荐

【Flink】The return type of function ‘Custom Source‘ could not be determined automatically
在定义Flink数据源的时候出现了下面的错误 Exception in thread "main" org.apache.flink.api.common.functions.In ...
【已解决 Flink Java API问题】The return type of function ‘xxx‘ could not be determined automatically
Flink Java API不像Scala API可以随便写lambda表达式,写完以后需要使用returns方法显式指定返回值类型,否则会报下面错误,大概意思就是说Java的lambda表达式不能提 ...
The return type of function ‘main(WordCountToObject.java:28)‘ could not be determined automatically,
java使用lamda表达式,出现类型无法自动识别到报一下异常在这Exception in thread "main" org.apache.flink.api.common.f ...
The return type of function ‘Custom Source‘ could not be determined automatically, due to type erasu
问题描述 Flink 在使用自定义一个 Source 时,抛出错误解决办法在自定义 Source时, 需要指定泛型
Flink使用lambda表达式报错：InvalidTypesException：could not be determined automatically, due to type erasure.
在写Flink程序的时候(以最简单的WordCount案例为例),有时会使用Lambda表达式来简化,如下边程序中的flatMap算子和Map算子处,都是用了Lambda表达式来简写: public ...
Flink启动报错could not be determined automatically
今天发布Flink应用,报如下错误: The return type of function 'main(RyeCollectorLauncher.java:77)' could not be det ...
'main' : function should return a value; 'void' return type assumed/////undeclared identifier
'main' : function should return a value; 'void' return type assumed 'c' : undeclared identifier 在调试c ...
记一个bug : C2555 overriding virtual function return type differs and is not covariant from
今天同事遇到一个编译错误找我帮忙看一下.原以为编译错误应该好解决,没想到搞了半天才fix,在此记录一下. 由于公司代码涉及机密且比较复杂,不方便贴出来,因此我写了一个简化的例子来展示这个编译错误是如何 ...
error C2556: 'void __thiscall......overloaded function differs only by return type from 'int __thisc
error C2556: 'void __thiscall......overloaded function differs only by return type from 'int __thisc ...

Flink InvalidTypesException: The return type of function could not be determined automatically...

Flink InvalidTypesException: The return type of function could not be determined automatically...

Flink InvalidTypesException: The return type of function could not be determined automatically...相关推荐

最新文章

热门文章