complex-event-processing - Esper：由于验证错误，EPL“选择”失败

Question

我正在尝试使用 Esper 运行一个简单的测试（第 14 章，http://dl.e-book-free.com/2013/07/activiti_in_action.pdf）。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)");

  ...
}

我收到有关 EPL 部分的错误消息：

"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)]

任何想法为什么会发生这种情况？

Answer 1

如果您希望 Esper 读取和/或写入事件类中的事件属性，则需要为事件属性提供 JavaBean getter 和 setter。为了使您的示例正常工作，您需要添加一个像这样的吸气剂：

public class LoanRequestEvent {
    public int amount =2;

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

    public int getAmount() {
        return amount;
    }
}