4.1、Flink任务怎样读取集合中的数据

1、API说明

非并行数据源：
        def fromElements[T: TypeInformation](data: T*): DataStream[T]
        def fromCollection[T: TypeInformation](data: Seq[T]): DataStream[T] 
        def fromCollection[T: TypeInformation] (data: Iterator[T]): DataStream[T] 

并行数据源：
        def fromParallelCollection[T: TypeInformation] (data: SplittableIterator[T])

使用场景：

        常用来调试代码使用

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2、这是一个完整的入门案例

开发语言：Java1.8

Flink版本：flink1.17.0

package com.baidu.datastream.source;import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;
import org.apache.flink.util.NumberSequenceIterator;import java.util.Arrays;
import java.util.List;// --------------------------------------------------------------------------------------------
//  TODO 从集合中读取数据
// --------------------------------------------------------------------------------------------/**  TODO 通过`读取Java集合中数据`来创建 DataStreamSource**  方法1：fromCollection*        Collection、Iterator -> DataStreamSource*  方法2：fromElements*        OUT... data -> DataStreamSource*  方法3：fromParallelCollection*        SplittableIterator -> DataStreamSource*  重要提示：*       fromCollection、fromElements 创建的是非并行source算子(并行度只能为1)*       fromParallelCollection 创建的是并行算子(并行度>=1)* */public class ReadCollection {public static void main(String[] args) throws Exception {fromCollection();//fromElements();//fromParallelCollection();}public static void fromCollection() throws Exception {// 1.获取执行环境StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();env.setParallelism(3);// 2.读取Java集合数据List<String> list = Arrays.asList("刘备", "张飞", "关羽", "赵云", "马超", "黄忠");env.fromCollection(list).print();// 3.触发程序执行env.execute();}public static void fromElements() throws Exception {// 1.获取执行环境StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();env.setParallelism(3);// 2.读取给定的对象序列env.fromElements("刘备", "张飞", "关羽", "赵云", "马超", "黄忠").print();// 3.触发程序执行env.execute();}public static void fromParallelCollection() throws Exception {// 1.获取执行环境StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();env.setParallelism(3);// 2.读取给定的对象序列NumberSequenceIterator numberSequenceIterator = new NumberSequenceIterator(1, 10);env.fromParallelCollection(numberSequenceIterator, Long.class).print();/** 注意： fromParallelCollection生成的source为并行算子*       集合中的数据会被平均分配到并行子任务中去* */// 3.触发程序执行env.execute();}
}