Apache Flink:自定义InputFormat仅以1的并行度运行

我正在为Apache Flink实现一种自定义输入格式。我创建了一个虚拟输入格式,它返回3行。

public class ElasticsearchInputFormat extends GenericInputFormat<Row> {
    @Override
    public void configure(Configuration parameters) {
        System.out.println("configuring");
    }

    @Override
    public BaseStatistics getStatistics(BaseStatistics cachedStatistics) throws IOException {
        return cachedStatistics;
    }

    @Override
    public void open(GenericInputSplit split) throws IOException {
        System.out.println("opening: " + split);
        super.open(split);
    }

    @Override
    public void close() throws IOException {
        System.out.println("closing");
        super.close();
    }

    private int a = 0;

    public boolean reachedEnd() throws IOException {
        a++;
        return a > 3;
    }

    public Row nextRecord(Row reuse) throws IOException {
        Row r = new Row(2);
        r.setField(0, "osman");
        r.setField(1, "wow");
        return r;
    }
}

我的示例代码如下:

final ExecutionEnvironment env = ExecutionEnvironment.createCollectionsEnvironment();
env.setParallelism(8);

DataSource<Row> input = env.createInput(new ElasticsearchInputFormat());

input.print();

但是,尽管并行度设置为8,但它会打印:

configuring
opening: GenericSplit (0/1)
closing
osman,wow
osman,wow
osman,wow

为什么它没有并行化?我希望有多个拆分,以便其他操作符可以并行使用它。