content: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You under the Apache License, Version 2.0
   * (the "License"); you may not use this file except in compliance with
   * the License.  You may obtain a copy of the License at
   *
   *    http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.spark.examples.streaming;
  
  import com.google.common.io.Closeables;
  
  import org.apache.spark.SparkConf;
  import org.apache.spark.api.java.function.FlatMapFunction;
  import org.apache.spark.api.java.function.Function2;
  import org.apache.spark.api.java.function.PairFunction;
  import org.apache.spark.storage.StorageLevel;
  import org.apache.spark.streaming.Duration;
  import org.apache.spark.streaming.api.java.JavaDStream;
  import org.apache.spark.streaming.api.java.JavaPairDStream;
  import org.apache.spark.streaming.api.java.JavaReceiverInputDStream;
  import org.apache.spark.streaming.api.java.JavaStreamingContext;
  import org.apache.spark.streaming.receiver.Receiver;
  import scala.Tuple2;
  
  import java.io.BufferedReader;
  import java.io.InputStreamReader;
  import java.net.ConnectException;
  import java.net.Socket;
  import java.nio.charset.StandardCharsets;
  import java.util.Arrays;
  import java.util.Iterator;
  import java.util.regex.Pattern;
  
  /**
   * Custom Receiver that receives data over a socket. Received bytes is interpreted as
   * text and \n delimited lines are considered as records. They are then counted and printed.
   *
   * Usage: JavaCustomReceiver <master> <hostname> <port>
   *   <master> is the Spark master URL. In local mode, <master> should be 'local[n]' with n > 1.
   *   <hostname> and <port> of the TCP server that Spark Streaming would connect to receive data.
   *
   * To run this on your local machine, you need to first run a Netcat server
   *    `$ nc -lk 9999`
   * and then run the example
   *    `$ bin/run-example org.apache.spark.examples.streaming.JavaCustomReceiver localhost 9999`
   */
  
  public class JavaCustomReceiver extends Receiver<String> {
    private static final Pattern SPACE = Pattern.compile(" ");
  
    public static void main(String[] args) throws Exception {
      if (args.length < 2) {
        System.err.println("Usage: JavaCustomReceiver <hostname> <port>");
        System.exit(1);
      }
  
      StreamingExamples.setStreamingLogLevels();
  
      // Create the context with a 1 second batch size
      SparkConf sparkConf = new SparkConf().setAppName("JavaCustomReceiver");
      JavaStreamingContext ssc = new JavaStreamingContext(sparkConf, new Duration(1000));
  
      // Create an input stream with the custom receiver on target ip:port and count the
      // words in input stream of \n delimited text (eg. generated by 'nc')
      JavaReceiverInputDStream<String> lines = ssc.receiverStream(
        new JavaCustomReceiver(args[0], Integer.parseInt(args[1])));
      JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, String>() {
        @Override
        public Iterator<String> call(String x) {
          return Arrays.asList(SPACE.split(x)).iterator();
        }
      });
      JavaPairDStream<String, Integer> wordCounts = words.mapToPair(
        new PairFunction<String, String, Integer>() {
          @Override public Tuple2<String, Integer> call(String s) {
            return new Tuple2<>(s, 1);
          }
        }).reduceByKey(new Function2<Integer, Integer, Integer>() {
          @Override
          public Integer call(Integer i1, Integer i2) {
            return i1 + i2;
          }
        });
  
      wordCounts.print();
      ssc.start();
      ssc.awaitTermination();
    }
  
    // ============= Receiver code that receives data over a socket ==============
  
    String host = null;
    int port = -1;
  
    public JavaCustomReceiver(String host_ , int port_) {
      super(StorageLevel.MEMORY_AND_DISK_2());
      host = host_;
      port = port_;
    }
  
    public void onStart() {
      // Start the thread that receives data over a connection
      new Thread()  {
        @Override public void run() {
          receive();
        }
      }.start();
    }
  
    public void onStop() {
      // There is nothing much to do as the thread calling receive()
      // is designed to stop by itself isStopped() returns false
    }
  
    /** Create a socket connection and receive data until receiver is stopped */
    private void receive() {
      try {
        Socket socket = null;
        BufferedReader reader = null;
        String userInput = null;
        try {
          // connect to the server
          socket = new Socket(host, port);
          reader = new BufferedReader(
              new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8));
          // Until stopped or connection broken continue reading
          while (!isStopped() && (userInput = reader.readLine()) != null) {
            System.out.println("Received data '" + userInput + "'");
            store(userInput);
          }
        } finally {
          Closeables.close(reader, /* swallowIOException = */ true);
          Closeables.close(socket,  /* swallowIOException = */ true);
        }
        // Restart in an attempt to connect again when server is active again
        restart("Trying to connect again");
      } catch(ConnectException ce) {
        // restart if could not connect to server
        restart("Could not connect", ce);
      } catch(Throwable t) {
        restart("Error receiving data", t);
      }
    }
  }
  