Flink DataStream读写Kafka

Flink提供了Kafka连接器，用于从或向Kafka读写数据。

本文总结Flink与Kafka集成中的问题,并对一些疑点进行总结和梳理。

问题一: 读Kafka的方式

## 读取一个Topic
FlinkKafkaConsumer010#FlinkKafkaConsumer010(String topic, DeserializationSchema<T> valueDeserializer, Properties props)
FlinkKafkaConsumer010#FlinkKafkaConsumer010(String topic, KafkaDeserializationSchema<T> deserializer, Properties props)
举例: 
    FlinkKafkaConsumer010<String> kafkaConsumer = new FlinkKafkaConsumer010<>("userActionLog1", new SimpleStringSchema(), kafkaProperties);
    DataStream<String> source = env.addSource(kafkaConsumer).name("KafkaSource").uid("source-id");

## 读取多个Topic
FlinkKafkaConsumer010#FlinkKafkaConsumer010(List<String> topics, DeserializationSchema<T> deserializer, Properties props)
FlinkKafkaConsumer010#FlinkKafkaConsumer010(List<String> topics, KafkaDeserializationSchema<T> deserializer, Properties props)
举例:
    FlinkKafkaConsumer010<String> kafkaConsumer = new FlinkKafkaConsumer010<>(Arrays.asList("userActionLog1","userActionLog2","userActionLog3"), new SimpleStringSchema(), kafkaProperties);
    DataStream<String> source = env.addSource(kafkaConsumer).name("KafkaSource").uid("source-id");
    

# 读取多个Topic
FlinkKafkaConsumer010#FlinkKafkaConsumer010(Pattern subscriptionPattern, DeserializationSchema<T> valueDeserializer, Properties props)
FlinkKafkaConsumer010#FlinkKafkaConsumer010(Pattern subscriptionPattern, KafkaDeserializationSchema<T> deserializer, Properties props)
举例:
    FlinkKafkaConsumer010<String> kafkaConsumer = new FlinkKafkaConsumer010<>(Pattern.compile("userActionLog[1-9]{1}"), new SimpleStringSchema(), kafkaProperties);
    DataStream<String> source = env.addSource(kafkaConsumer).name("KafkaSource").uid("source-id");
    
# 从指定的时间戳开始消费
kafkaConsumer.setStartFromTimestamp(long startupOffsetsTimestamp)

# 从指定的偏移量开始消费,可为每个分区单独设置偏移量
kafkaConsumer.setStartFromSpecificOffsets(Map<KafkaTopicPartition, Long> specificStartupOffsets)
    

问题二: 读Kafka与反序列化器

可通过org.apache.flink.api.common.serialization.DeserializationSchema或org.apache.flink.streaming.connectors.kafka.KafkaDeserializationSchema,将从Kafka读取的二进制字节流反序列化成Flink内部支持的Java/Scala对象。

Flink内置支持以下2种常用反序列化器:

1. org.apache.flink.api.common.serialization.SimpleStringSchema:反序列化成String。

2. org.apache.flink.streaming.util.serialization.JSONKeyValueDeserializationSchema:反序列化成jackson ObjectNode。

如果想实现Kafka复杂JSON直接转换成想要的Object，可仿照org.apache.flink.api.common.serialization.SimpleStringSchema自定义即可。主要实现deserialize反序列化方法。

问题三: 读Kafka动态发现Topic、Partition

之前使用Spark Streaming，Spark 2.2.2不支持动态发现Kafka 0.10.1中新增的Topic(基于正则指定)和Partition。当新增了Topic或Partition，需要重启Spark Streaming任务。

在Flink中, 默认支持动态发现Kafka中新增的Topic或Partition，但需要手动开启。

kafkaProperties.put("flink.partition-discovery.interval-millis","10000");

flink.partition-discovery.interval-millis: 检查间隔,单位毫秒。

问题四: 读Kafka与Exactly Once语义

没有开启Checkpoint，默认自动提交Offset至外部存储(如Kafka Broker或Zookeeper),自动提交的间隔是5秒。Flink Kafka Consumer的容错依赖于自动提交的Offset。

开启Checkpoint,默认在Checkpoint完成后将存储在Checkpoint中的Offset再提交至外部存储(如Kafka Broker或0.8版本中的Zookeeper)，Flink Kafka Consumer在Flink作业运行过程中的容错依赖于Checkpoint中的Offset，Flink作业恢复，则可能是从Checkpoint中的Offset恢复，也可能是从外部存储如Kafka Broker中的Offset恢复，具体取决于恢复方式。注意: 在这种方式下，Kafka Broker(或0.8中Zookeeper)存储的Offset仅用于监控消费进度。

总结，基于Kafka可重复消费的能力并结合Flink Checkpoint机制，Flink Kafka Consumer能提供Exactly-Once语义。

问题五: 写Kafka与Exactly Once语义

• Kafka 0.8 Flink不提供Exactly-Once或At-Least-Once语义。

• Kafka 0.9、0.10 Flink启用Checkpoint,FlinkKafkaProducer09和FlinkKafkaProducer010提供At-Least-Once语义。除此之外，还需设置以下参数:

  setLogFailuresOnly(false): 若为true,Producer遇到异常时,仅记录失败时的日志,流处理程序继续。需要设置为false,当遇到异常,流处理程序失败,抛出异常恢复任务并重试发送。

  setFlushOnCheckpoint(true): Checkpoint中包含Kafka Producer Buffer中的数据，设置为true, 确保Checkpoint成功前，Buffer中的所有记录都已写入Kafka。

  retries: 重试次数,默认0,建议设置更大。

• Kafka 0.11、1.0.0+ Flink启用Checkpoint，基于Two Phase Commit,FlinkKafkaProducer011和FlinkKafkaProducer(Kafka >=1.0.0) 默认提供Exactly-Once语义。
  如需要其他语义Semantic.NONE(可能会丢或重)、Semantic.AT_LEAST_ONCE(可能会重)、Semantic.EXACTLY_ONCE(默认)，可手动选择。

从Kafka 0.10.1读数据并写入到Kafka 0.11.0.3并实现PV统计

项目依赖

<dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.13</version>
        </dependency>

        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.13</version>
        </dependency>

        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-java</artifactId>
            <version>1.8.0</version>
        </dependency>

        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-streaming-java_2.11</artifactId>
            <version>1.8.0</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.5</version>
        </dependency>


        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-connector-kafka-0.10_2.11</artifactId>
            <version>1.8.0</version>
        </dependency>

        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-connector-kafka-0.11_2.11</artifactId>
            <version>1.8.0</version>
        </dependency>

        <dependency>
            <groupId>org.apache.kafka</groupId>
            <artifactId>kafka-clients</artifactId>
            <version>0.11.0.3</version>
        </dependency>

        <dependency>
            <groupId>org.apache.flink</groupId>
            <artifactId>flink-runtime-web_2.11</artifactId>
            <version>1.8.0</version>
        </dependency>

代码实现

package com.bigdata.flink;

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import org.apache.flink.api.common.functions.AggregateFunction;
import org.apache.flink.api.common.functions.FilterFunction;
import org.apache.flink.api.common.functions.MapFunction;
import org.apache.flink.api.common.serialization.SimpleStringSchema;
import org.apache.flink.api.common.typeinfo.TypeHint;
import org.apache.flink.api.java.functions.KeySelector;
import org.apache.flink.api.java.tuple.Tuple4;
import org.apache.flink.api.java.utils.ParameterTool;
import org.apache.flink.configuration.ConfigConstants;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.configuration.RestOptions;
import org.apache.flink.runtime.state.StateBackend;
import org.apache.flink.runtime.state.filesystem.FsStateBackend;
import org.apache.flink.streaming.api.CheckpointingMode;
import org.apache.flink.streaming.api.TimeCharacteristic;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.datastream.SingleOutputStreamOperator;
import org.apache.flink.streaming.api.environment.CheckpointConfig;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.streaming.api.functions.timestamps.BoundedOutOfOrdernessTimestampExtractor;
import org.apache.flink.streaming.api.functions.windowing.WindowFunction;
import org.apache.flink.streaming.api.windowing.assigners.TumblingEventTimeWindows;
import org.apache.flink.streaming.api.windowing.time.Time;
import org.apache.flink.streaming.api.windowing.windows.TimeWindow;
import org.apache.flink.streaming.connectors.kafka.FlinkKafkaConsumer010;
import org.apache.flink.streaming.connectors.kafka.FlinkKafkaProducer011;
import org.apache.flink.streaming.connectors.kafka.internals.KeyedSerializationSchemaWrapper;
import org.apache.flink.util.Collector;

import java.text.Format;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Properties;

/**
 * Author: Wang Pei
 * Summary: 读写Kafka
 */
public class ReadWriteKafka {
    public static void main(String[] args) throws Exception{

        /**解析命令行参数*/
        ParameterTool fromArgs = ParameterTool.fromArgs(args);
        ParameterTool parameterTool = ParameterTool.fromPropertiesFile(fromArgs.getRequired("applicationProperties"));

        //checkpoint参数
        String checkpointDirectory = parameterTool.getRequired("checkpointDirectory");
        long checkpointSecondInterval = parameterTool.getLong("checkpointSecondInterval");

        //fromKafka参数
        String fromKafkaBootstrapServers = parameterTool.getRequired("fromKafka.bootstrap.servers");
        String fromKafkaGroupID = parameterTool.getRequired("fromKafka.group.id");
        String fromKafkaAutoOffsetReset= parameterTool.getRequired("fromKafka.auto.offset.reset");
        String fromKafkaTopic = parameterTool.getRequired("fromKafka.topic");

        //toKafka参数
        String toKafkaBootstrapServers = parameterTool.getRequired("toKafka.bootstrap.servers");
        String toKafkaTopic = parameterTool.getRequired("toKafka.topic");

        //窗口参数
        long tumblingWindowLength = parameterTool.getLong("tumblingWindowLength");
        long outOfOrdernessSeconds = parameterTool.getLong("outOfOrdernessSeconds");


        /**配置运行环境*/

        //设置Local Web Server
        Configuration config = new Configuration();
        config.setInteger(RestOptions.PORT,8081);
        config.setBoolean(ConfigConstants.LOCAL_START_WEBSERVER, true);
        StreamExecutionEnvironment env = StreamExecutionEnvironment.createLocalEnvironmentWithWebUI(config);

        env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);

        //设置StateBackend
        env.setStateBackend((StateBackend) new FsStateBackend(checkpointDirectory, true));

        //设置Checkpoint
        CheckpointConfig checkpointConfig = env.getCheckpointConfig();
        checkpointConfig.setCheckpointInterval(checkpointSecondInterval * 1000);
        checkpointConfig.setCheckpointingMode(CheckpointingMode.EXACTLY_ONCE);
        checkpointConfig.enableExternalizedCheckpoints(CheckpointConfig.ExternalizedCheckpointCleanup.RETAIN_ON_CANCELLATION);

        /**配置数据源*/
        Properties kafkaProperties = new Properties();
        kafkaProperties.put("bootstrap.servers",fromKafkaBootstrapServers);
        kafkaProperties.put("group.id",fromKafkaGroupID);
        kafkaProperties.put("auto.offset.reset",fromKafkaAutoOffsetReset);
        FlinkKafkaConsumer010<String> kafkaConsumer = new FlinkKafkaConsumer010<>(fromKafkaTopic, new SimpleStringSchema(), kafkaProperties);
        kafkaConsumer.setCommitOffsetsOnCheckpoints(true);
        DataStream<String> source = env.addSource(kafkaConsumer).name("KafkaSource").uid("source-id");

        /**抽取转换*/
        SingleOutputStreamOperator<Tuple4<String, String, String, Integer>> sourceMap = source
                .map((MapFunction<String, Tuple4<String, String, String, Integer>>) value -> {
                    Tuple4<String, String, String, Integer> output = new Tuple4<>();
                    try {
                        JSONObject obj = JSON.parseObject(value);
                        output.f0 = obj.getString("userID");
                        output.f1 = obj.getString("eventTime");
                        output.f2 = obj.getString("eventType");
                        output.f3 = obj.getInteger("productID");
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return output;
                    }).returns(new TypeHint<Tuple4<String, String, String, Integer>>(){})
                .name("Map: ExtractTransform").uid("map-id");

        /**过滤掉异常数据*/
        SingleOutputStreamOperator<Tuple4<String, String, String, Integer>> sourceFilter = sourceMap
                .filter((FilterFunction<Tuple4<String, String, String, Integer>>) value -> value != null)
                .name("Filter: FilterExceptionData").uid("filter-id");


        /**抽取时间戳并发射水印*/
        SingleOutputStreamOperator<Tuple4<String, String, String, Integer>> assignTimestampsAndWatermarks = sourceFilter.assignTimestampsAndWatermarks(new BoundedOutOfOrdernessTimestampExtractor<Tuple4<String, String, String, Integer>>(Time.seconds(outOfOrdernessSeconds)) {

            SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
            @Override
            public long extractTimestamp(Tuple4<String, String, String, Integer> element) {

                long timestamp = 0L;

                try {
                    Date date = format.parse(element.f1);
                    timestamp = date.getTime();
                } catch (ParseException e) {
                    e.printStackTrace();
                }

                return timestamp;
            }
        }).uid("watermark-id");


        /**窗口统计*/
        SingleOutputStreamOperator<String> aggregate = assignTimestampsAndWatermarks
                //默认用Hash方式
                .keyBy((KeySelector<Tuple4<String, String, String, Integer>, String>) value -> value.f2)
                .window(TumblingEventTimeWindows.of(Time.seconds(tumblingWindowLength)))
                //在每个窗口(Window)上应用WindowFunction(CustomWindowFunction)
                //CustomAggFunction用于增量聚合
                //在每个窗口上，先进行增量聚合(CustomAggFunction),然后将增量聚合的结果作为WindowFunction(CustomWindowFunction)的输入,计算后并输出
                //具体: 可参考底层AggregateApplyWindowFunction的实现
                .aggregate(new CustomAggFunction(), new CustomWindowFunction());

        //aggregate.print();

        /**结果输出*/
        Properties kafkaProducerProperties = new Properties();
        kafkaProducerProperties.setProperty("bootstrap.servers",toKafkaBootstrapServers);
        kafkaProducerProperties.setProperty("transaction.timeout.ms",60000+"");
        FlinkKafkaProducer011<String> kafkaProducer011 = new FlinkKafkaProducer011<>(
                toKafkaTopic,
                new KeyedSerializationSchemaWrapper<>(new SimpleStringSchema()),
                kafkaProducerProperties,
                FlinkKafkaProducer011.Semantic.EXACTLY_ONCE
        );

        aggregate.addSink(kafkaProducer011).name("outputToKafka");

        env.execute();

    }

    /**
     * 自定义AggregateFunction
     * 增量聚合，这里实现累加效果
     */
    static class CustomAggFunction implements AggregateFunction<Tuple4<String, String, String, Integer>,Long,Long> {

        @Override
        public Long createAccumulator() {
            return 0L;
        }

        @Override
        public Long add(Tuple4<String, String, String, Integer> value, Long accumulator) {
            return accumulator + 1;
        }

        @Override
        public Long getResult(Long accumulator) {
            return accumulator;
        }

        @Override
        public Long merge(Long accumulator1, Long accumulator2) {
            return accumulator1 + accumulator2;
        }
    }

    /**
     * 自定义WindowFunction
     * 对增量聚合的结果再做处理，并输出
     */
    static class CustomWindowFunction implements WindowFunction<Long, String,String, TimeWindow> {

        @Override
        public void apply(String key, TimeWindow window, Iterable<Long> input, Collector<String> out) throws Exception {

            Format format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

            long windowStart = window.getStart();
            long windowEnd = window.getEnd();
            Long windowPV = input.iterator().next();

            String output=format.format(new Date(windowStart))+","+format.format(new Date(windowEnd))+","+key+","+windowPV;

            out.collect(output);

        }
    }

}