Flink Operators 实战基础篇

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本文将介绍Map，FlatMap，Filter，KeyBy，Reduce和Aggregations的基本用法。

DataStream Transformations基础

Map

定义

Transformation	Description
DataStream → DataStream	Applies a Map transformation on a DataStream. The transformation calls a MapFunction for each element of the DataStream. Each MapFunction call returns exactly one element. The user can also extend RichMapFunction to gain access to other features provided by the RichFunctioninterface.

说明

利用map方法对每个数据进行一个转换，输入数据和输出数据为1对1的关系

样例

代码

public class MapDemo {
    public static void main(String[] args) throws Exception {
        final StreamExecutionEnvironment env = StreamExecutionEnvironment.createLocalEnvironment();
        env.setParallelism(1);

        DataStream<Integer> myInts = env.fromElements(1, 2, 3, 4, 5)
                .map(x -> x + 1);

        myInts.print("map");
        env.execute("Map Demo");
    }
}

输出结果

map> 2
map> 3
map> 4
map> 5
map> 6

说明

通过map将每个元素加1后输出

FlatMap

定义

Transformation	Description
DataStream → DataStream	Applies a FlatMap transformation on a DataStream. The transformation calls a FlatMapFunction for each element of the DataStream. Each FlatMapFunction call can return any number of elements including none. The user can also extend RichFlatMapFunction to gain access to other features provided by the RichFunction interface.

说明

利用flatMap方法对每个数据进行一个转换，输入数据和输出数据为1对n的关系，n大于等于0。此方法可以将一行数据拆成多行。

样例

代码

public class FlatMapDemo {
    public static void main(String[] args) throws Exception {
        final StreamExecutionEnvironment env = StreamExecutionEnvironment.createLocalEnvironment();
        env.setParallelism(1);

        DataStream<String> myStr = env.fromElements("1, 2, 3, 4, 5")
                .flatMap(new FlatMapFunction<String, String>() {
                    @Override
                    public void flatMap(String value, Collector<String> out) throws Exception {
                        for (String word : value.split(",")) {
                            out.collect(word.trim());
                        }
                    }
                });

        myStr.print("flatMap");
        env.execute("FlatMap Demo");
    }
}

输出结果

flatMap> 1
flatMap> 2
flatMap> 3
flatMap> 4
flatMap> 5

说明

通过flatMap将一行数据按照分隔符分割成多行输出

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