本文为《Flink大数据项目实战》学习笔记，想通过视频系统学习Flink这个最火爆的大数据计算框架的同学，推荐学习课程：
Flink大数据项目实战：http://t.cn/EJtKhaz
1. DataStream Transformation
1.1 DataStream转换关系
上图标识了DataStream不同形态直接的转换关系，也可以看出DataStream主要包含以下几类：
1.keyby就是按照指定的key分组
2.window是一种特殊的分组(基于时间)
3.coGroup
4.join Join是cogroup 的特例
5.Connect就是松散联盟，类似于英联邦
1.2 DataStream
DataStream 是 Flink 流处理 API 中最核心的数据结构。它代表了一个运行在多个分区上的并行流。
一个 DataStream 可以从 StreamExecutionEnvironment 通过env.addSource(SourceFunction) 获得。
1.3 map&flatMap
含义：数据映射(1进1出和1进n出)
转换关系：DataStream → DataStream
使用场景：
ETL时删减计算过程中不需要的字段
案例1：
public class TestMap {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Long> input=env.generateSequence(0,10);
DataStream plusOne=input.map(new MapFunction<Long, Long>() {
@Override
public Long map(Long value) throws Exception {
System.out.println("--------------------"+value);
return value+1;
}
});
plusOne.print();
env.execute();
}
}
案例2：
public class TestFlatmap {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<String> input=env.fromElements(WORDS);
DataStream<String> wordStream=input.flatMap(new FlatMapFunction<String, String>() {
@Override
public void flatMap(String value, Collector<String> out) throws Exception {
String[] tokens = value.toLowerCase().split("\W+");
for (String token : tokens) {
if (token.length() > 0) {
out.collect(token);
}
}
}
});
wordStream.print();
env.execute();
}
public static final String[] WORDS = new String[] {
"To be, or not to be,--that is the question:--",
"Whether 'tis nobler in the mind to suffer",
"The slings and arrows of outrageous fortune",
"And by opposing end them?--To die,--to sleep,--",
"Be all my sins remember'd."
};
}
如右上图所示，DataStream 各个算子会并行运行，算子之间是数据流分区。如 Source 的第一个并行实例（S1）和 flatMap() 的第一个并行实例（m1）之间就是一个数据流分区。而在 flatMap() 和 map() 之间由于加了 rebalance()，它们之间的数据流分区就有3个子分区（m1的数据流向3个map()实例）。这与 Apache Kafka 是很类似的，把流想象成 Kafka Topic，而一个流分区就表示一个 Topic Partition，流的目标并行算子实例就是 Kafka Consumers。
1.4 filter
含义：数据筛选(满足条件event的被筛选出来进行后续处理)，根据FliterFunction返回的布尔值来判断是否保留元素，true为保留，false则丢弃
转换关系： DataStream → DataStream
使用场景：
过滤脏数据、数据清洗等
案例：
public class TestFilter {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Long> input=env.generateSequence(-5,5);
input.filter(new FilterFunction<Long>() {
@Override
public boolean filter(Long value) throws Exception {
return value>0;
}
}).print();
env.execute();
}
}
1.5 keyBy
含义：
根据指定的key进行分组(逻辑上把DataStream分成若干不相交的分区，key一样的event会被划分到相同的partition，内部采用hash分区来实现)
转换关系： DataStream → KeyedStream
限制：
1.可能会出现数据倾斜，可根据实际情况结合物理分区来解决(后面马上会讲到)
2.Key的类型限制:
1）不能是没有覆盖hashCode方法的POJO
2）不能是数组
使用场景：
1.分组(类比SQL中的分组
案例：
public class TestKeyBy {
public static void main(String[] args) throws Exception {
//统计各班语文成绩最高分是谁
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Tuple4<String,String,String,Integer>> input=env.fromElements(TRANSCRIPT);
KeyedStream<Tuple4<String,String,String,Integer>,Tuple> keyedStream = input.keyBy("f0");
keyedStream.maxBy("f3").print();
env.execute();
}
public static final Tuple4[] TRANSCRIPT = new Tuple4[] {
Tuple4.of("class1","张三","语文",100),
Tuple4.of("class1","李四","语文",78),
Tuple4.of("class1","王五","语文",99),
Tuple4.of("class2","赵六","语文",81),
Tuple4.of("class2","钱七","语文",59),
Tuple4.of("class2","马二","语文",97)
};
}
1.6 KeyedStream
KeyedStream用来表示根据指定的key进行分组的数据流。
一个KeyedStream可以通过调用DataStream.keyBy()来获得。
在KeyedStream上进行任何transformation都将转变回DataStream。
在实现中，KeyedStream是把key的信息写入到了transformation中。
每个event只能访问所属key的状态，其上的聚合函数可以方便地操作和保存对应key的状态。
1.7 reduce&fold& Aggregations
分组之后当然要对分组之后的数据也就是KeyedStream进行各种聚合操作啦(想想SQL)。
KeyedStream → DataStream
对于KeyedStream的聚合操作都是滚动的(rolling，在前面的状态基础上继续聚合)，千万不要理解为批处理时的聚合操作(DataSet，其实也是滚动聚合，只不过他只把最后的结果给了我们)。
案例1：
public class TestReduce {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Tuple4<String,String,String,Integer>> input=env.fromElements(TRANSCRIPT);
KeyedStream<Tuple4<String,String,String,Integer>,Tuple> keyedStream = input.keyBy(0)
keyedStream.reduce(new ReduceFunction<Tuple4<String, String, String, Integer>>() {
@Override
public Tuple4<String, String, String, Integer> reduce(Tuple4<String, String, String, Integer> value1, Tuple4<String, String, String, Integer> value2) throws Exception {
value1.f3+=value2.f3;
return value1;
}
}).print();
env.execute();
}
public static final Tuple4[] TRANSCRIPT = new Tuple4[] {
Tuple4.of("class1","张三","语文",100),
Tuple4.of("class1","李四","语文",78),
Tuple4.of("class1","王五","语文",99),
Tuple4.of("class2","赵六","语文",81),
Tuple4.of("class2","钱七","语文",59),
Tuple4.of("class2","马二","语文",97)
};
}
案例2：
public class TestFold {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Tuple4<String,String,String,Integer>> input=env.fromElements(TRANSCRIPT);
DataStream<String> result =input.keyBy(0).fold("Start", new FoldFunction<Tuple4<String,String,String,Integer>,String>() {
@Override
public String fold(String accumulator, Tuple4<String, String, String, Integer> value) throws Exception {
return accumulator + "=" + value.f1;
}
});
result.print();
env.execute();
}
public static final Tuple4[] TRANSCRIPT = new Tuple4[] {
Tuple4.of("class1","张三","语文",100),
Tuple4.of("class1","李四","语文",78),
Tuple4.of("class1","王五","语文",99),
Tuple4.of("class2","赵六","语文",81),
Tuple4.of("class2","钱七","语文",59),
Tuple4.of("class2","马二","语文",97)
};
}
1.8 Interval join
KeyedStream,KeyedStream → DataStream
在给定的周期内，按照指定的key对两个KeyedStream进行join操作，把符合join条件的两个event拉到一起，然后怎么处理由用户你来定义。
key1 == key2 && e1.timestamp + lowerBound <= e2.timestamp <= e1.timestamp + upperBound
场景：把一定时间范围内相关的分组数据拉成一个宽表
案例：
public class TestIntervalJoin {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime);
DataStream<Transcript> input1=env.fromElements(TRANSCRIPTS).assignTimestampsAndWatermarks(new AscendingTimestampExtractor<Transcript>() {
@Override
public long extractAscendingTimestamp(Transcript element) {
return element.time;
}
});
DataStream<Student> input2=env.fromElements(STUDENTS).assignTimestampsAndWatermarks(new AscendingTimestampExtractor<Student>() {
@Override
public long extractAscendingTimestamp(Student element) {
return element.time;
}
});
KeyedStream<Transcript,String> keyedStream=input1.keyBy(new KeySelector<Transcript, String>() {
@Override
public String getKey(Transcript value) throws Exception {
return value.id;
}
});
KeyedStream<Student,String> otherKeyedStream=input2.keyBy(new KeySelector<Student, String>() {
@Override
public String getKey(Student value) throws Exception {
return value.id;
}
});
//e1.timestamp + lowerBound <= e2.timestamp <= e1.timestamp + upperBound
// key1 == key2 && leftTs - 2 < rightTs < leftTs + 2
keyedStream.intervalJoin(otherKeyedStream)
.between(Time.milliseconds(-2), Time.milliseconds(2))
.upperBoundExclusive()
.lowerBoundExclusive()
.process(new ProcessJoinFunction<Transcript, Student, Tuple5<String,String,String,String,Integer>>()
@Override
public void processElement(Transcript transcript, Student student, Context ctx, Collector<Tuple5<String, String, String, String, Integer>> out) throws Exception {
out.collect(Tuple5.of(transcript.id,transcript.name,student.class_,transcript.subject,transcript.score));
}
}).print();
env.execute();
}
public static final Transcript[] TRANSCRIPTS = new Transcript[] {
new Transcript("1","张三","语文",100,System.currentTimeMillis()),
new Transcript("2","李四","语文",78,System.currentTimeMillis()),
new Transcript("3","王五","语文",99,System.currentTimeMillis()),
new Transcript("4","赵六","语文",81,System.currentTimeMillis()),
new Transcript("5","钱七","语文",59,System.currentTimeMillis()),
new Transcript("6","马二","语文",97,System.currentTimeMillis())
};
public static final Student[] STUDENTS = new Student[] {
new Student("1","张三","class1",System.currentTimeMillis()),
new Student("2","李四","class1",System.currentTimeMillis()),
new Student("3","王五","class1",System.currentTimeMillis()),
new Student("4","赵六","class2",System.currentTimeMillis()),
new Student("5","钱七","class2",System.currentTimeMillis()),
new Student("6","马二","class2",System.currentTimeMillis())
};
private static class Transcript{
private String id;
private String name;
private String subject;
private int score;
private long time;
public Transcript(String id, String name, String subject, int score, long time) {
this.id = id;
this.name = name;
this.subject = subject;
this.score = score;
this.time = time;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSubject() {
return subject;
}
public void setSubject(String subject) {
this.subject = subject;
}
public int getScore() {
return score;
}
public void setScore(int score) {
this.score = score;
}
public long getTime() {
return time;
}
public void setTime(long time) {
this.time = time;
}
}
private static class Student{
private String id;
private String name;
private String class_;
private long time;
public Student(String id, String name, String class_, long time) {
this.id = id;
this.name = name;
this.class_ = class_;
this.time = time;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getClass_() {
return class_;
}
public void setClass_(String class_) {
this.class_ = class_;
}
public long getTime() {
return time;
}
public void setTime(long time) {
this.time = time;
}
}
}
1.9 connect & union(合并流)
connect之后生成ConnectedStreams，会对两个流的数据应用不同的处理方法，并且双流 之间可以共享状态(比如计数)。这在第一个流的输入会影响第二个流 时, 会非常有用; union 合并多个流，新的流包含所有流的数据。
union是DataStream* → DataStream。
connect只能连接两个流，而union可以连接多于两个流 。
connect连接的两个流类型可以不一致，而union连接的流的类型必须一致。
案例：
public class TestConnect {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Long> someStream = env.generateSequence(0,10);
DataStream<String> otherStream = env.fromElements(WORDS);
ConnectedStreams<Long, String> connectedStreams = someStream.connect(otherStream);
DataStream<String> result=connectedStreams.flatMap(new CoFlatMapFunction<Long, String, String>() {
@Override
public void flatMap1(Long value, Collector<String> out) throws Exception {
out.collect(value.toString());
}
@Override
public void flatMap2(String value, Collector<String> out) {
for (String word: value.split("\W+")) {
out.collect(word);
}
}
});
result.print();
env.execute();
}
public static final String[] WORDS = new String[] {
"And thus the native hue of resolution",
"Is sicklied o'er with the pale cast of thought;",
"And enterprises of great pith and moment,",
"With this regard, their currents turn awry,",
"And lose the name of action.--Soft you now!",
"The fair Ophelia!--Nymph, in thy orisons",
"Be all my sins remember'd."
};
}
1.10 CoMap, CoFlatMap
跟map and flatMap类似，只不过作用在ConnectedStreams上
ConnectedStreams → DataStream
1.11 split & select(拆分流)
split
1.DataStream → SplitStream
2.按照指定标准将指定的DataStream拆分成多个流用SplitStream来表示
select
1.SplitStream → DataStream
2.跟split搭配使用，从SplitStream中选择一个或多个流
案例：
public class TestSplitAndSelect {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<Long> input=env.generateSequence(0,10);
SplitStream<Long> splitStream = input.split(new OutputSelector<Long>() {
@Override
public Iterable<String> select(Long value) {
List<String> output = new ArrayList<String>();
if (value % 2 == 0) {
output.add("even");
}
else {
output.add("odd");
}
return output;
}
});
//splitStream.print();
DataStream<Long> even = splitStream.select("even");
DataStream<Long> odd = splitStream.select("odd");
DataStream<Long> all = splitStream.select("even","odd");
//even.print();
odd.print();
//all.print();
env.execute();
}
}
1.12 project
含义：从Tuple中选择属性的子集
限制：
1.仅限event数据类型为Tuple的DataStream
2.仅限Java API
使用场景：
ETL时删减计算过程中不需要的字段
案例：
public class TestProject {
public static void main(String[] args) throws Exception {
final StreamExecutionEnvironment env=StreamExecutionEnvironment.getExecutionEnvironment();
DataStreamSource<Tuple4<String,String,String,Integer>> input=env.fromElements(TRANSCRIPT);
DataStream<Tuple2<String, Integer>> out = input.project(1,3);
out.print();
env.execute();
}
public static final Tuple4[] TRANSCRIPT = new Tuple4[] {
Tuple4.of("class1","张三","语文",100),
Tuple4.of("class1","李四","语文",78),
Tuple4.of("class1","王五","语文",99),
Tuple4.of("class2","赵六","语文",81),
Tuple4.of("class2","钱七","语文",59),
Tuple4.of("class2","马二","语文",97)
};
}
1.13 assignTimestampsAndWatermarks
含义：提取记录中的时间戳作为Event time，主要在window操作中发挥作用，不设置默认就是ProcessingTim
限制：
只有基于event time构建window时才起作用
使用场景：
当你需要使用event time来创建window时，用来指定如何获取event的时间戳
案例：讲到window时再说
1.14 window相关Operators
放在讲解完Event Time之后在细讲
构建window
1.window
2.windowAl
window上的操作
1.Window ApplyWindow Reduce
2.Window Fold
3.Aggregations on windows(sum、min、max、minBy、maxBy)
4.Window Join
5.Window CoGroup
2. 物理分区
2.1回顾 Streaming DataFlow
2.2并行化DataFlow
2.3算子间数据传递模式
One-to-one streams
保持元素的分区和顺序
Redistributing streams
1.改变流的分区
2.重新分区策略取决于使用的算子
a）keyBy() (re-partitions by hashing the key)
b）broadcast()
c）rebalance() (which re-partitions randomly)
2.4物理分区
能够对分区在物理上进行改变的算子如下图所示：
上面算子都是Transformation，只是改变了分区。它们都是DataStream → DataStream。
2.5 rescale
通过轮询调度将元素从上游的task一个子集发送到下游task的一个子集。
原理：
第一个task并行度为2，第二个task并行度为6，第三个task并行度为2。从第一个task到第二个task，Src的子集Src1 和 Map的子集Map1，2，3对应起来，Src1会以轮询调度的方式分别向Map1，2，3发送记录。从第二个task到第三个task，Map的子集1，2，3对应Sink的子集1，这三个流的元素只会发送到Sink1。假设我们每个TaskManager有三个Slot，并且我们开了SlotSharingGroup，那么通过rescale，所有的数据传输都在一个TaskManager内，不需要通过网络。
2.6任务链和资源组相关操作
startNewChain()表示从这个操作开始，新启一个新的chain。
someStream.filter(...).map(...).startNewChain().map(...)
如上一段操作，表示从map()方法开始，新启一个新的chain。
如果禁用任务链可以调用disableChaining()方法。
如果想单独设置一个SharingGroup，可以调用slotSharingGroup("name")方法。
