java Lombok @Builder 不初始化集合
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Lombok @Builder not initializing collections
提问by marstran
I am using Lombok's @Dataand @Builderannotations like this:
我正在使用 Lombok@Data和@Builder这样的注释：
@Data
@Builder(toBuilder = true)
class Movie {
// Some other fields here.
private final List<Actor> actors;
}
When I create a new Movieusing the builder, without specifying any actors, I would expect Lombok to initialize my List to Collections.emptyList(). But this does not happen:
当我Movie使用构建器创建一个新的时，没有指定任何演员，我希望 Lombok 将我的 List 初始化为Collections.emptyList(). 但这不会发生：
List<Actor> actors = Movie.builder().build().getActors();
System.out.println(actors); // Prints 'null'.
In the documentation for the @Builderannotation, it is stated at line 55 and 56 in the code-example for Vanilla Java (https://projectlombok.org/features/Builder.html) that I should look at the code example for @Singular(https://projectlombok.org/features/Singular-snippet.html). At line 112 in the Vanilla Java example here, it seems like the list should be initialized to the empty list.
在@Builder注释的文档中，它在 Vanilla Java 的代码示例 ( https://projectlombok.org/features/Builder.html) 的第 55 和 56 行中说明，我应该查看@Singular( https: //projectlombok.org/features/Singular-snippet.html）。在此处的 Vanilla Java 示例的第 112 行，该列表似乎应该初始化为空列表。
I checked, and it does indeed happen if I annotate the list with @Singular:
我查了一下，如果我用以下内容注释列表，确实会发生@Singular：
@Data
@Builder(toBuilder = true)
class Movie {
// Some other fields here.
@Singular
private final List<Actor> actors;
}
List<Actor> actors = Movie.builder().build().getActors();
System.out.println(actors); // Prints '[]'.
Is this a bug in Lombok, or is there something that I am doing wrong? According to the documentation, it seems like the list should be initialized to the empty list in both cases (because the @Builderdoc refers to the @Singulardoc).
这是龙目岛的错误，还是我做错了什么？根据文档，在这两种情况下，列表似乎都应该初始化为空列表（因为@Builder文档指的是@Singular文档）。
回答by Roel Spilker
Only when you use @Singular, you get an empty list. On the Builder documentation pageit says:
只有当你使用时@Singular，你才会得到一个空列表。在Builder 文档页面上，它说：
…with the
@Singularannotation, lombok will treat that builder node as a collection.
...使用
@Singular注释，lombok 会将构建器节点视为一个集合。
Without the @Singular, lombok treats it as any other object. So it will be nullinstead of an empty Collection.
如果没有@Singular，lombok 会将其视为任何其他对象。所以它将null不是一个空的集合。
Disclosure: I am a Lombok developer
披露：我是龙目岛的开发人员
