Java 8 - 从列表中过滤空字符串不起作用

Java 8 - filter empty string from List not working

提问by Alexander Nikolov

I would like to remove an empty String from the List of Strings.

我想从字符串列表中删除一个空字符串。

Here is what I tried, using the stream API:

这是我尝试过的，使用流 API：

list.stream().filter(item-> item.isEmpty()).collect(Collectors.toList());

After that empty string is still present in the list. What am I missing?

之后，空字符串仍然存在于列表中。我错过了什么？

回答by JB Nizet

filter()keepsthe elements that match the predicate. Soyou need the inverse predicate:

filter()保留与谓词匹配的元素。所以你需要逆谓词：

list.stream().filter(item-> !item.isEmpty()).collect(Collectors.toList());

This will also not modify the original list. It will create a filtered copy of the original list. So you need

这也不会修改原始列表。它将创建原始列表的过滤副本。所以你需要

list = list.stream().filter(item-> !item.isEmpty()).collect(Collectors.toList());

If you want to modify the original list, you should use

如果要修改原始列表，则应使用

list.removeIf(item -> item.isEmpty());

or simply

或者干脆

list.removeIf(String::isEmpty);

回答by Peter Lawrey

I suspect you are not keeping the result. The result is returned, the original list is not altered as this is functional programming style.

我怀疑你没有保留结果。结果被返回，原始列表没有改变，因为这是函数式编程风格。

list = list.stream().filter(item-> !item.trim().isEmpty()).collect(Collectors.toList());

回答by lczapski

Since java 11 there is a new method Predicate::not.

从 java 11 开始，有一个新方法Predicate::not。

So you can write it like that:

所以你可以这样写：

list.stream().filter(Predicate.not(String::isEmpty)).collect(Collectors.toList())

回答by Adam Siemion

Maybe the string contains whitespaces? Replace item -> item.isEmpty()with item -> !item.trim().isEmpty()

也许字符串包含空格？替换item -> item.isEmpty()为item -> !item.trim().isEmpty()

回答by ΦXoc? ? Пepeúpa ツ

you are collecting the empty elements :)

您正在收集空元素:)

you want the not empty so invert the predicate

你想要非空所以反转谓词

List<String> xxx = list.stream().filter(item -> !item.isEmpty()).collect(Collectors.toList());

additionally, the stream is not modifying the original list, so Collect(Collectrors.toList())is returning the result of the predicate :)

此外，流没有修改原始列表，因此Collect(Collectrors.toList())返回谓词的结果:)

回答by Sangram Badi

you can follow below example, it may help you

你可以按照下面的例子，它可能会帮助你

String[] firstArray = {"test1", "", "test2", "test4", "", null};

    firstArray = Arrays.stream(firstArray).filter(s -> (s != null && s.length() > 0)).toArray(String[]::new);

回答by printfabcd

     <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.5-SNAPSHOT</version>
        </dependency>

import org.apache.commons.lang3.StringUtils;
        //Java8 new api
        strings.removeIf(StringUtils::isBlank);
        //stream        strings=strings.stream().filter(StringUtils::isNotBlank).collect(Collectors.toList());

回答by Mohammed Imran

Might be your List contains null. So first filter with null check then again filter on empty

可能是您的列表包含空值。所以首先过滤空检查然后再次过滤空

    list.stream().filter(item -> null != item).filter(item -> !item.isEmpty()).collect(Collectors.toList());

If you have apache commons lang lib use Apache StringUtils isNotBlank

如果你有 apache commons lang lib 使用 Apache StringUtils isNotBlank

list.stream().filter(item -> StrinUtils.isNotBlank(item)).collect(Collectors.toList());

回答by ernest_k

You are removing non-empty strings (check your filter condition). Try:

您正在删除非空字符串（检查您的过滤条件）。尝试：

list.stream().filter(item -> !item.isEmpty()).collect(Collectors.toList());

Otherwise, you may need to check that you're removing blanks as well:

否则，您可能需要检查是否也删除了空格：

list.stream().filter(item -> !item.trim().isEmpty()).collect(Collectors.toList());

回答by Andrei Olar

You are not removing empty Strings from the list, you were retrieving them. Your filter condition is wrong.

您不是从列表中删除空字符串，而是在检索它们。您的过滤条件错误。

Try like this:

像这样尝试：

List<String> collect = list.stream().filter(item -> !item.trim().isEmpty()).collect(Collectors.toList());