如何根据 Java 中属性的值将对象列表转换为字符串列表?

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英文:

How transform a list of objects to a list of strings based on the value of a property in java?

问题

有没有一种方法可以根据属性的值将对象列表转换为字符串列表?我有一个名为Tag的实体类。

public class Tag {

    private int tagID;
    private String description;
}

我获得了一组带有它们的ID和描述的标签:

[Tag [tagID=1, description=121], Tag [tagID=1, description=244], Tag [tagID=1, description=331], Tag [tagID=2, description=244], Tag [tagID=2, description=122]]

我需要的是:

List<String> output = ["121,244,331", "244,122"]

到目前为止,我组装了以下代码:

String description = tags.stream().map(Tag::getDescription).collect(Collectors.joining(";"));

这将为一个标签输出结果:

String description = "121,244,331"

当然,我可以通过循环运行它并将结果附加到数组,但我想知道是否有一种更加优雅的方法,甚至是一行代码?

英文:

Is there a way how to transform a list of objects to a list of strings based on the value of a property? I have an entity Tag

public class Tag {

	private int tagID;
	private String description;
}

I get a list of tags with their ids and descriptions:

[Tag [tagID=1, description=121], Tag [tagID=1, description=244], Tag [tagID=1, description=331], Tag [tagID=2, description=244], Tag [tagID=2, description=122]]

And what I need is:

List&lt;String&gt; output = [&quot;121,244,331&quot;, &quot;244,122&quot;]

So far I put together this:

String description = tags.stream().map(Tag::getDescription).collect(Collectors.joining( &quot;;&quot; ));

outputting a result for one tag

String description = &quot;121,244,331&quot;

Of course, I could run it through a loop and append the result to an array, but I wondered if there is a more ellegant way - even a one-liner?

答案1

得分: 5

你可以使用 Collectors.groupingBy 按标签 ID 进行分组,然后使用 Collectors.joining 连接描述。

List<String> res = new ArrayList<>(tagList.stream().collect(
        Collectors.groupingBy(Tag::getTagID,
                Collectors.mapping(Tag::getDescription, Collectors.joining(",")))).values());
英文:

You can use Collectors.groupingBy to group by tag id and then join description using Collectors.joining

List&lt;String&gt; res = new ArrayList&lt;&gt;(tagList.stream().collect(
                        Collectors.groupingBy(Tag::getTagID,
                                Collectors.mapping(Tag::getDescription, Collectors.joining(&quot;,&quot;)))).values());

答案2

得分: 2

我认为你正在寻找以下内容:

List<String> result = tags.stream()
        .collect(Collectors.groupingBy(Tag::getTagID))
        .values()
        .stream()
        .map(t -> t.stream().map(Tag::getDescription).collect(Collectors.joining(";")))
        .collect(Collectors.toList());

输出

[121;244;331, 244;122]
英文:

I think you are looking to:

List&lt;String&gt; result = tags.stream()
        .collect(Collectors.groupingBy(Tag::getTagID))
        .values()
        .stream()
        .map(t -&gt; t.stream().map(Tag::getDescription).collect(Collectors.joining( &quot;;&quot; )))
        .collect(Collectors.toList());

Output

[121;244;331, 244;122]

huangapple
  • 本文由 发表于 2020年7月22日 04:38:01
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