java 使用 Spring 通过构造函数自动装配集合
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Autowiring a collection via the constructor with Spring
提问by Guillaume
I have what seems to be a simple problem, as stated in the title. Here is the kind of class I have :
正如标题中所述，我遇到了一个看似简单的问题。这是我的课程类型：
public class Foo {
@Autowired
public Foo(@Qualifier("bar") Set<String> bar) {
// ...
}
}
Which I try to run with the following spring context :
我尝试使用以下 spring 上下文运行：
<context:annotation-config />
<util:set id="bar">
<value>tata</value>
<value>titi</value>
<value>toto</value>
</util:set>
<bean id="foo" class="Foo" />
This fails to run with :
这无法运行：
No matching bean of type [java.lang.String] found for dependency [collection of java.lang.String]: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Qualifier(value=bar)}
没有为依赖项 [java.lang.String 的集合] 找到类型为 [java.lang.String] 的匹配 bean：预期至少有 1 个 bean 有资格作为此依赖项的自动装配候选者。依赖注解：{@org.springframework.beans.factory.annotation.Qualifier(value=bar)}
Note that if I add other parameters to my constructor, it works fine. If I use setter injection, it works fine. I'm sure I miss something obvious ... do you know what ?
请注意，如果我向构造函数添加其他参数，则它可以正常工作。如果我使用 setter 注入，它工作正常。我确定我错过了一些明显的东西......你知道吗？
回答by Christian Semrau
Autowiring collections is not possible using the @Autowiredannotation. An autowired collection means "to provide all beans of a particular type". Using the JSR-250 @Resourceannotation, you can declare that you want a resource injected by its name, not its type. Or you inject the dependency explicitly.
使用@Autowired注释无法自动装配集合。自动装配的集合意味着“提供特定类型的所有 bean”。使用 JSR-250@Resource注释，您可以声明您希望通过其名称而不是其类型注入资源。或者您显式注入依赖项。
[...] beans which are themselves defined as a collection or map type cannot be injected via
@Autowiredsince type matching is not properly applicable to them. Use@Resourcefor such beans, referring to the specific collection/map bean by unique name.
[...] 本身定义为集合或映射类型的 bean 不能通过注入，
@Autowired因为类型匹配不适用于它们。使用@Resource的唯一名称等豆类，指的是特定集合/图豆。
See the Spring documentationfor more details.
有关更多详细信息，请参阅Spring 文档。
回答by mrembisz
As others stated it is impossible to use @Autowired for Strings and collections of String. You can use @Value with spring EL here assuming you have spring in version 3:
正如其他人所说，不可能将@Autowired 用于字符串和字符串集合。假设您在版本 3 中有 spring，您可以在此处将 @Value 与 spring EL 一起使用：
public class Foo {
@Autowired
public Foo(@Value("#{bar}") Set<String> bar) {
// ...
}
}
回答by entpnerd
I had this same problem and was inspired by @rembisz's answer. That answer didn't work on my version of Spring (4.1.3). When I checked the SpEL documentation on bean references, I found a different SpEL syntax to express bean references in autowired values that worked for me - @beanname. As such, the following code worked for me:
我遇到了同样的问题，并受到@rembisz 的回答的启发。该答案不适用于我的 Spring (4.1.3) 版本。当我检查有关 bean 引用的SpEL 文档时，我发现了一种不同的 SpEL 语法来表达对我有用的自动装配值中的 bean 引用 - @beanname。因此，以下代码对我有用：
public class Foo {
@Autowired
public Foo(@Value("#{@bar}") Set<String> bar) {
// ...
}
}
回答by skaffman
I thinkthis is because Spring interprets the autowiring of a collection as "give me all beans of type String", rather than "give me the bean which is a collection of String". The error message supports that idea.
我认为这是因为 Spring 将集合的自动装配解释为“给我所有类型的 bean String”，而不是“给我一个集合的 bean String”。错误消息支持这个想法。
I don't think you can use autowiring for this. Short of manually wiring it up in the XML, the best I can suggest is:
我认为您不能为此使用自动装配。没有在 XML 中手动连接它，我能建议的最好的方法是：
public class Foo {
private @Resource Set<String> bar;
}
