Fang Yong created FLINK-7010:
--------------------------------
Summary: Lamdba expression in flatMap throws InvalidTypesException
in DataSet
Key: FLINK-7010
URL: https://issues.apache.org/jira/browse/FLINK-7010
Project: Flink
Issue Type: Bug
Reporter: Fang Yong
When I create an example and use lambda in flatMap as follows
{{
ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();
DataSet<String> source = env.fromCollection(
Lists.newArrayList("hello", "flink", "test", "flat", "map", "lambda"));
DataSet<Tuple2<Integer, String>> tupled = source.flatMap((word, out) -> {
int length = word.length();
out.collect(Tuple2.of(length, word));
});
try {
tupled.print();
} catch (Exception e) {
throw new RuntimeException(e);
}
}}
InvalidTypesException was throwed and the exception stack is as follows:
{{
Caused by: org.apache.flink.api.common.functions.InvalidTypesException: The
return type of function 'testFlatMap(FlatMapTest.java:20)' 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.collect(DataSet.java:407)
at org.apache.flink.api.java.DataSet.print(DataSet.java:1605)
Caused by: org.apache.flink.api.common.functions.InvalidTypesException: The
generic type parameters of 'Collector' are missing.
It seems that your compiler has not stored them into the .class file.
Currently, only the Eclipse JDT compiler preserves the type information
necessary to use the lambdas feature type-safely.
See the documentation for more information about how to compile jobs containing
lambda expressions.
at
org.apache.flink.api.java.typeutils.TypeExtractor.validateLambdaGenericParameter(TypeExtractor.java:1653)
at
org.apache.flink.api.java.typeutils.TypeExtractor.validateLambdaGenericParameters(TypeExtractor.java:1639)
at
org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:573)
at
org.apache.flink.api.java.typeutils.TypeExtractor.getFlatMapReturnTypes(TypeExtractor.java:188)
at org.apache.flink.api.java.DataSet.flatMap(DataSet.java:266)
}}
The 20th line code is {{ DataSet<Tuple2<Integer, String>> tupled =
source.flatMap((word, out) -> { }}
When I use FlatMapFunction instead of lambda, it will be all right
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