Java 8 流字符串空或空过滤器
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Java 8 Stream String Null Or Empty Filter
提问by ServerSideCat
I've got Google Guava inside Stream:
我在 Stream 中有 Google Guava：
this.map.entrySet().stream()
.filter(entity -> !Strings.isNullOrEmpty(entity.getValue()))
.map(obj -> String.format("%s=%s", obj.getKey(), obj.getValue()))
.collect(Collectors.joining(","))
As you see there is a statement !String.isNullOrEmpty(entity)inside the filter function.
如您所见!String.isNullOrEmpty(entity)，过滤器函数中有一条语句。
I don't want to use Guava anymore in the project, so I just want to replace it simply by:
我不想在项目中再使用 Guava，所以我只想简单地替换它：
string == null || string.length() == 0;
How can I do it more elegant?
我怎样才能做得更优雅？
采纳答案by fge
You can write your own predicate:
您可以编写自己的谓词：
final Predicate<Map.Entry<?, String>> valueNotNullOrEmpty
= e -> e.getValue() != null && !e.getValue().isEmpty();
Then just use valueNotNullOrEmptyas your filter argument.
然后只需valueNotNullOrEmpty用作您的过滤器参数。
回答by Olivier Grégtheitroade
You can create your own Stringsclass with your own predicate:
您可以Strings使用自己的谓词创建自己的类：
public class Strings {
public static boolean isNotNullOrEmpty (String str) {
return str != null && !str.isEmpty();
}
}
Then in your code:
然后在你的代码中：
.filter(Strings::isNotNullOrEmpty)
But as @fge mentionned, you can't use that on a Map.Entry<?,?>...
但正如@fge 所提到的，你不能在Map.Entry<?,?>......
回答by rvertigo
If you prefer to use commons-lang3, StringUtils has
如果你更喜欢使用 commons-lang3，StringUtils 有
isEmpty()isNotEmpty()isBlank()isNotBlank()
isEmpty()isNotEmpty()isBlank()isNotBlank()
These methods can be used in filters as method references:
这些方法可以在过滤器中用作方法引用：
this.stringList.stream().filter(StringUtils::isNotBlank);
or as lambdas:
或作为 lambdas：
this.stringList.stream().filter(s -> StringUtils.isNotBlank(s));
回答by shmosel
You can break down the filter into two steps:
您可以将过滤器分解为两个步骤：
this.map.entrySet().stream()
.filter(entity -> entity.getValue() != null)
.filter(entity -> !entity.getValue().isEmpty())
.map(obj -> String.format("%s=%s", obj.getKey(), obj.getValue()))
.collect(Collectors.joining(","))
On a side note, most Map.Entry.toString()implementations do exactly what you're doing in map(), so you could theoretically just do map(Map.Entry::toString). But I wouldn't rely on that unless you're producing a toString()or something that doesn't require documented or deterministic behavior.
在一个侧面说明，大多数Map.Entry.toString()的实现做你在做什么map()，所以你可以在理论上只是做map(Map.Entry::toString)。但我不会依赖它，除非你正在生产toString()不需要记录或确定性行为的东西。
Also, I know you want to abandon Guava, but here's a solution that might make you reconsider:
另外，我知道您想放弃 Guava，但这里有一个可能会让您重新考虑的解决方案：
Joiner.on(',').withKeyValueSeparator("=")
.join(Maps.filterValues(map, Predicates.not(Strings::isNullOrEmpty)));
回答by Taras Melnyk
It works for me: list.stream().filter(el-> el != null && !el.toString().trim().isEmpty()).collect(Collectors.toList());
这个对我有用： list.stream().filter(el-> el != null && !el.toString().trim().isEmpty()).collect(Collectors.toList());
回答by lczapski
In java 11 there is a new method Predicate::not.
在 java 11 中有一个新方法Predicate::not。
So you can filter out empty string :
所以你可以过滤掉空字符串：
list.stream()
.filter(Objects::nonNull)
.filter(Predicate.not(String::isEmpty))
