英文:
How to filter and log null objects in Java 8 streams
问题
我正努力理解Java 8的流(Streams)并想知道是否有人可以帮助我。
在旧版Java中，
List<Obj> newObjs = new ArrayList<Obj>();for (Obj obj : objects) {if (obj == null) {logger.error("null object");} else {newObjs.add(...);}}
基本上，我想要过滤掉空对象并将其记录到日志中。
在Java 8中有什么好的方法可以做到这一点？
英文:
I am trying to wrap my head around java8 streams and was wondering if someone can help me with it.
In old java,
List<Obj> newObjs = ArrayList<Obj>();for (Obj obj : objects){if(obj == null){logger.error("null object");}else{newObjs.add(...)}}
Basically, I want to filter null objects and also log it.
What's a good way to do this in java 8?
答案1
得分: 5
我建议将该逻辑移到不同的方法中。
public boolean filter(Object obj) {if (obj == null) {logger.error("null object");return false;}return true;}
然后只需对列表进行流处理。
objects.stream().filter(this::filter).collect(Collectors.toList());
英文:
I would suggest to move that logic into different method
public boolean filter(Object obj) {if(obj == null){logger.error("null object");return false;}return true;}
And then just stream the list
objects.stream().filter(this::filter).collect(Collectors.toList());
答案2
得分: 4
你可以使用 peek 方法，并在其中放置一个 if 语句：
List<Obj> newObjs = objects.stream().peek(x -> {if (x == null) logger.error("null object");}).filter(Objects::nonNull).collect(Collectors.toList());
但这种方式会使流失去简洁性，所以个人而言，对于像“过滤空对象并收集到列表中”这样的简单操作，我仍然会使用普通的 for 循环。
请记住，流 不能 替代 for 循环。不要仅仅因为流是新的和时髦的就使用它们。
英文:
You can use peek and put an if statement inside it:
List<Obj> newObjs = objects.stream().peek(x -> {if (x == null) logger.error("null object");}).filter(Objects::nonNull).collect(Collectors.toList());
But this kind of loses the conciseness of the streams, so personally I would still use a plain old for loop for something simple like "filtering nulls and collecting to a list".
Keep in mind that Streams do not replace for loops. Don't use streams just because it's new and shiny.
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