Flink has a rich set of APIs using which developers can perform transformations on both batch and real-time data. A variety of transformations includes mapping, filtering, sorting, joining, grouping and aggregating. These transformations by Apache Flink are performed on distributed data. Let us discuss the different APIs Apache Flink offers.

Dataset API

Dataset API in Apache Flink is used to perform batch operations on the data over a period. This API can be used in Java, Scala and Python. It can apply different kinds of transformations on the datasets like filtering, mapping, aggregating, joining and grouping.

Datasets are created from sources like local files or by reading a file from a particular sourse and the result data can be written on different sinks like distributed files or command line terminal. This API is supported by both Java and Scala programming languages.

Here is a Wordcount program of Dataset API −

public class WordCountProg {
   public static void main(String[] args) throws Exception {
      final ExecutionEnvironment env = ExecutionEnvironment.getExecutionEnvironment();

      DataSet<String> text = env.fromElements(
      "Hello",
      "My Dataset API Flink Program");

      DataSet<Tuple2<String, Integer>> wordCounts = text
      .flatMap(new LineSplitter())
      .groupBy(0)
      .sum(1);

      wordCounts.print();
   }

   public static class LineSplitter implements FlatMapFunction<String, Tuple2<String, Integer>> {
      @Override
      public void flatMap(String line, Collector<Tuple2<String, Integer>> out) {
         for (String word : line.split(" ")) {
            out.collect(new Tuple2<String, Integer>(word, 1));
         }
      }
   }
}

DataStream API

This API is used for handling data in continuous stream. You can perform various operations like filtering, mapping, windowing, aggregating on the stream data. There are various sources on this data stream like message queues, files, socket streams and the result data can be written on different sinks like command line terminal. Both Java and Scala programming languages support this API.

Here is a streaming Wordcount program of DataStream API, where you have continuous stream of word counts and the data is grouped in the second window.

import org.apache.flink.api.common.functions.FlatMapFunction;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.util.Collector;
public class WindowWordCountProg {
   public static void main(String[] args) throws Exception {
      StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
      DataStream<Tuple2<String, Integer>> dataStream = env
      .socketTextStream("localhost", 9999)
      .flatMap(new Splitter())
      .keyBy(0)
      .timeWindow(Time.seconds(5))
      .sum(1);
      dataStream.print();
      env.execute("Streaming WordCount Example");
   }
   public static class Splitter implements FlatMapFunction<String, Tuple2<String, Integer>> {
      @Override
      public void flatMap(String sentence, Collector<Tuple2<String, Integer>> out) throws Exception {
         for (String word: sentence.split(" ")) {
            out.collect(new Tuple2<String, Integer>(word, 1));
         }
      }
   }
}