The generic type parameters of ‘Tuple2‘ are missing. In many cases lambda methods don‘t provide

想在使用datastream api 开发的时候，对于多个字段开窗的时候，刚开始是逐个排序，但是影响性能。所以想把两个字段一起来排序，就遇到以下问题。

Exception in thread "main" org.apache.flink.api.common.functions.InvalidTypesException: 
The generic type parameters of 'Tuple2' 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.java.functions.KeySelector' interface.
Otherwise the type has to be specified explicitly using type information.
	at org.apache.flink.api.java.typeutils.TypeExtractionUtils.validateLambdaType(TypeExtractionUtils.java:371)
	at org.apache.flink.api.java.typeutils.TypeExtractor.getUnaryOperatorReturnType(TypeExtractor.java:565)
	at org.apache.flink.api.java.typeutils.TypeExtractor.getKeySelectorTypes(TypeExtractor.java:412)
	at org.apache.flink.api.java.typeutils.TypeExtractor.getKeySelectorTypes(TypeExtractor.java:403)
	at org.apache.flink.streaming.api.datastream.KeyedStream.(KeyedStream.java:116)
	at org.apache.flink.streaming.api.datastream.DataStream.keyBy(DataStream.java:293)

  // 避免flink java的泛型擦除 写法
        SingleOutputStreamOperator operator = singleOutputStreamOperator.keyBy(new KeySelector>() {
            @Override
            public Tuple2 getKey(Snapshot snapshot) throws Exception {
                return Tuple2.of(snapshot.getDateTime(), snapshot.getHsSecurityId());
            }
        }).flatMap(new SnapshotProcessFunction());