使用java stream过滤谓词时记录过滤器的结果 [英] Logging the result of filter while using java streams filter by predicate

问题描述

场景是我创建了不同类型的过滤器，它们根据对象的属性过滤一些对象的列表。

The scenario is there are different types of filters I have created which filters the list of some objects based on the property of the object.

所以为此我创建了一个每个过滤器继承的AbstractObjectFilter类。

AbstractObjectFilter.java

So for that I have created an AbstractObjectFilter class which inherited by every filter.
AbstractObjectFilter.java

public abstract class AbstractEventFilter
{
    protected abstract Predicate<IEvent> isEligible();

    public List<IEvent> getFilteredEvents(final List<IEvent> events)
    {
        return events.stream().filter(isEligible()).collect(Collectors.toList());
    }
}

所以现在每个过滤器都会扩展此类并覆盖isEligible （）并在该函数中，它根据其属性返回谓词。

So now every filter extends this class and overrides the isEligible() and in that function it returns the predicate based on its properties.

例如： -
MinNumOfPrizesFilter.java

For eg:- MinNumOfPrizesFilter.java

public class MinimumNumOfPrizesFilter extends AbstractEventFilter
{
    private int minimumNumOfPrizes;

    public MinimumNumOfPrizesFilter(@NonNull int minimumNumOfPrizes)
    {
        this.minimumNumOfPrizes = minimumNumOfPrizes;
    }

    @Override
    protected Predicate<IEvent> isEligible()
    {
        return event -> event.getPrizeCount() >= minimumNumOfPrizes;
    }
}

同样，我创建了许多其他过滤器。有一个applyFilter函数迭代过滤器对象列表，并通过调用getFilteredEvents函数继续应用过滤器。

Similarly there are many other filters I have created. There is one applyFilter function which iterate over the list of filter objects and keep applying filter by call getFilteredEvents function.

现在我如何记录每个事件的命运例如 - x1事件由MinNumOfPrizesFilter过滤器过滤.x1的奖金数量 - 10，所需的最低奖金数量 - 20

Now how can i log the fate of each event For example - "x1 event was filtered by MinNumOfPrizesFilter filter. x1's prize count - 10 , required min prize count - 20"

推荐答案

你可以简单地在lambda表达式中添加括号并在验证之前添加日志记录语句：

You can simply add brackets to your lambda expression and add the logging statement right before the validation :

return event -> {
    // LOG.info(event.getName() + " was filtered...") or whatever you use for logging.
    return event.getPrizeCount() >= minimumNumOfPrizes;
}

请注意，存在 peek 主要用于登录java流的操作：

Note that there exists a peek operation which is meant to be used mostly for logging on java streams :

events.stream()
      .peek(event -> System.out.println("Filtering event" + event.getName()))
      .filter(isEligible())
      .collect(Collectors.toList());

但这在这里没有帮助，因为你需要登录 AbstractEventFilter implements。

but that is not helping here, as you need to log in AbstractEventFilter implementations.

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