Question

我在Esper中做了一个基于长度窗口的程序。但是当窗口已满时，上一个事件应该成为一个旧事件。当我尝试在updateListener中打印那个旧事件时，我每次都变为null

EPServiceProvider sp = EPServiceProviderManager.getDefaultProvider();
    String qry = "select count(*) from com.bizruntime.Student.win:length(2)";

    EPStatement statement = sp.getEPAdministrator().createEPL(qry);

    MyListener listener = new MyListener();
    statement.addListener(listener);

    Student student1 = new Student(44,"xyz");
    Student student2= new Student(45,"pqr");
    Student student3 = new Student(43,"stu");
    Student student4 = new Student(41,"abc");
    sp.getEPRuntime().sendEvent(student1);
    sp.getEPRuntime().sendEvent(student2);
    sp.getEPRuntime().sendEvent(student3);
    sp.getEPRuntime().sendEvent(student4);

这是听众类：

    public void update(EventBean[] newEvent, EventBean[] oldEvent) {
    EventBean event = newEvent[0];

    System.out.println(oldEvent);
    System.out.println("Student Name :"+event.get("count(*)"));

     }

Answer 1

有一个“select rstream”，它为您提供与select子句中匹配的“remove stream”。如果select子句只是一个计数，则删除流是先前的计数。在您还需要一些事件输出的情况下，您可以查看事件聚合函数，如“last”或“window”或函数“prev”和“prior”。

如何在esper中获得旧事件？

1 个答案: