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前言：基础不牢，地动山摇。

1.不设置setParallelism代码

import org.apache.flink.streaming.api.scala.StreamExecutionEnvironment
import org.apache.flink.streaming.api.scala._

object SourceTest_fromCollectionTest {
  def main(args: Array[String]): Unit = {
    //获取执行环境
    val env = StreamExecutionEnvironment.getExecutionEnvironment

    //创建case class类
    case class IOT(id: Int, timestamp: Long, temperature: Double)

    //读取数据源
    val res: DataStream[IOT] = env.fromCollection(List(
      IOT(1, 1234678217, 21321.12),
      IOT(3, 1234678217, 21321.12),
      IOT(7, 1234678217, 21321.12),
      IOT(19, 1234678217, 21321.12),
      IOT(20, 1234678217, 21321.12),
      IOT(30, 1234678217, 21321.12),
      IOT(31, 1234678217, 21321.12),
      IOT(32, 1234678217, 21321.12),
      IOT(33, 1234678217, 21321.12),
      IOT(34, 1234678217, 21321.12),
      IOT(35, 1234678217, 21321.12)
    ))

    //打印输出
    res.print("Jackson_TestIOT")

    //执行
    env.execute()

  }

}

运行结果

Jackson_TestIOT:2> IOT(19,1234678217,21321.12)
Jackson_TestIOT:1> IOT(7,1234678217,21321.12)
Jackson_TestIOT:4> IOT(30,1234678217,21321.12)
Jackson_TestIOT:6> IOT(32,1234678217,21321.12)
Jackson_TestIOT:7> IOT(1,1234678217,21321.12)
Jackson_TestIOT:8> IOT(3,1234678217,21321.12)
Jackson_TestIOT:5> IOT(31,1234678217,21321.12)
Jackson_TestIOT:3> IOT(20,1234678217,21321.12)
Jackson_TestIOT:8> IOT(34,1234678217,21321.12)
Jackson_TestIOT:7> IOT(33,1234678217,21321.12)
Jackson_TestIOT:1> IOT(35,1234678217,21321.12)

Process finished with exit code 0

结论：默认情况不设置并行度，并行度则是由机器的核数决定。

2.设置setParallelism(1)代码

    //打印输出
    res.print("Jackson_TestIOT").setParallelism(1)

运行结果

Jackson_TestIOT> IOT(1,1234678217,21321.12)
Jackson_TestIOT> IOT(3,1234678217,21321.12)
Jackson_TestIOT> IOT(7,1234678217,21321.12)
Jackson_TestIOT> IOT(19,1234678217,21321.12)
Jackson_TestIOT> IOT(20,1234678217,21321.12)
Jackson_TestIOT> IOT(30,1234678217,21321.12)
Jackson_TestIOT> IOT(31,1234678217,21321.12)
Jackson_TestIOT> IOT(32,1234678217,21321.12)
Jackson_TestIOT> IOT(33,1234678217,21321.12)
Jackson_TestIOT> IOT(34,1234678217,21321.12)
Jackson_TestIOT> IOT(35,1234678217,21321.12)

Process finished with exit code 0

结论：并行度设置1，则所有的都是1,后面则不打印数值。

3.设置setParallelism(n)代码

n>=2,这里测试n取10

    //打印输出
    res.print("Jackson_TestIOT").setParallelism(10)

运行结果：

Jackson_TestIOT:9> IOT(32,1234678217,21321.12)
Jackson_TestIOT:8> IOT(31,1234678217,21321.12)
Jackson_TestIOT:10> IOT(33,1234678217,21321.12)
Jackson_TestIOT:5> IOT(19,1234678217,21321.12)
Jackson_TestIOT:4> IOT(7,1234678217,21321.12)
Jackson_TestIOT:1> IOT(34,1234678217,21321.12)
Jackson_TestIOT:7> IOT(30,1234678217,21321.12)
Jackson_TestIOT:6> IOT(20,1234678217,21321.12)
Jackson_TestIOT:3> IOT(3,1234678217,21321.12)
Jackson_TestIOT:2> IOT(1,1234678217,21321.12)
Jackson_TestIOT:2> IOT(35,1234678217,21321.12)

Process finished with exit code 0

结论：如果设置的并行度>数据条数，后面输出结果数值则不会重复。

           如果设置的并行度<数据条数，后面输出结果数值则会重复。

4.思考

在此给大家留下一个思考题

1.这个技术出现的背景、初衷和要达到什么样的目标或是要解决什么样的问题。
2. 这个技术的优势和劣势分别是什么，或者说，这个技术的 trade-off 是什么
3. 这个技术适用的场景。
4. 技术的组成部分和关键点。
5. 技术的底层原理和关键实现。
6. 已有的实现和它之间的对比。