Complex event processing Esper:EPL"；选择"；未能找到验证错误

我试图用Esper运行一个简单的测试（第14章）。代码非常简单：

public class EventLengthWindowTest {
  public class LoanRequestEvent {
    public int amount =2;

    public LoanRequestEvent(int a){
        amount += a;
    }
}

private int sumAmount = 0;

@Test
public void testEventLengthWindow() {
  Configuration configuration = new Configuration();
  configuration.addEventType(LoanRequestEvent.class); 

  EPServiceProvider epService = EPServiceProviderManager.getDefaultProvider(configuration);
  EPAdministrator admin = epService.getEPAdministrator();
  EPStatement epStatement = admin.createEPL("select sum(amount) as sumAmount from LoanRequestEvent.win:length(2)");

  ...
}

我收到一条关于EPL部件的错误消息：

"select sum(amount) as sumAmount from LoanRequestEvent.win:length(2)"

它说：

com.espertech.esper.client.EPStatementException: Error starting statement: Failed to validate select-clause expression 'sum(amount)': Property named 'amount' is not valid in any stream [select sum(amount) as sumAmount from LoanRequestEvent.win:length(2)]

---

知道为什么会发生这种情况吗？

如果您希望Esper读取和/或写入事件类中的事件属性，则需要为它们提供JavaBean getter和setter。要使示例正常工作，您需要添加一个getter，如下所示：

public class LoanRequestEvent {
    public int amount =2;

    public LoanRequestEvent(int a){
        amount += a;
    }

    public int getAmount() {
        return amount;
    }
}