如果要比较不同事件中字段的值，可以在 flatSelect 方法，只需使用一个非常简单的模式，而不需要任何 where 表达：
创建图案：

Pattern<MonitoringEvent, ?> warningPattern = Pattern.<MonitoringEvent>begin("First Event")
    .subtype(TemperatureEvent.class)
    .next("Second Event")
    .subtype(TemperatureEvent.class)
    .within(Time.seconds(10));

将模式应用于数据流：

PatternStream<MonitoringEvent> tempPatternStream = CEP.pattern(
    inputEventStream.keyBy("rackID"),
    warningPattern);

检查值并通过生成新的复杂事件 flatSelect 方法：

DataStream<TemperatureWarning> warnings = tempPatternStream.flatSelect(
    (Map<String, MonitoringEvent> pattern, Collector<TemperatureAlert> out) -> {
        TemperatureEvent first = (TemperatureEvent) pattern.get("First Event");
        TemperatureEvent second = (TemperatureEvent) pattern.get("Second Event");

        if (first.getTemperature() <= second.getTemperature()) {
            out.collect(new TemperatureWarning(
                first.getRackID(), 
                (first.getTemperature() + second.getTemperature()) / 2));
        }
    });