何时使用< optional> true</optional>以及何时使用< scope>提供的</scope> [英] When to use <optional>true</optional> and when to use <scope>provided</scope>
问题描述
由<optional>true</optional>或<scope>provided</scope>装饰的依赖项在传递性依赖项时将被忽略.我已阅读
the dependencies decorated by <optional>true</optional> or <scope>provided</scope> will be ignored when they are dependent transitively. I have read this, my understanding is like the difference between @Component and @Service in Spring, they only vary semantically. Is it right?
推荐答案
除注释外，还有一个更重要的 semantic 区别:容器应提供提供的"依赖项，因此，如果您的容器让您处于休眠状态，则应将休眠状态标记为已提供.
In addition to the comment, there is more important semantic difference: "Provided" dependencies are expected to be supplied by the container, so if your container gives you hibernate, you should mark hibernate as provided.
可选依赖项主要用于减轻某些库的传递负担.例如:如果您可以使用具有5种不同数据库类型的库，但是通常只需要一种，则可以将依赖于库的依赖项标记为可选，以便用户可以提供他实际使用的库.如果不这样做，则可能会遇到两种类型的问题:
Optional dependencies are mainly used to reduce the transitive burden of some libraries. For example: If you can use a library with 5 different database types, but you usually only require one, you can mark the library-dependent dependencies as optional, so that the user can supply the one he actually uses. If you don't do, you might get two types of problems:
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该库会提取大量的传递依赖关系，而实际上您几乎不需要这些传递依赖关系，因此您可以无故炸毁项目.
The library pulls a huge load of transitive dependencies of which you actually need very few so that you blow up your project without reason.
更危险的是:您可能会拉取两个具有重叠类的库，以使类加载器无法同时加载它们.这可能会导致您的库出现意外行为.
More dangerously: You might pull two libraries with overlapping classes, so that the class loader cannot load both of them. This might lead to unexpected behaviour of your library.
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