我有一个 bean，我想使用 Spring util 命名空间 <util:list id="myList"> 注入(inject)一个命名列表但是 Spring 正在寻找 String 类型的 bean 的集合。我的失败测试是:

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class ListInjectionTest {

    @Autowired @Qualifier("myList") private List<String> stringList;

    @Test public void testNotNull() {
        TestCase.assertNotNull("stringList not null", stringList);
    }
}

我的上下文是:

<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xmlns:util="http://www.springframework.org/schema/util"
   xmlns="http://www.springframework.org/schema/beans"
   xmlns:context="http://www.springframework.org/schema/context"
   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
   http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.5.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">

   <util:list id="myList">
       <value>foo</value>
       <value>bar</value>
   </util:list>

</beans>

但我明白了

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: 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.Autowired(required=true), @org.springframework.beans.factory.annotation.Qualifier(value=myList)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:726)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:571)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:412)

这让我感到困惑，因为我认为这将是预期的工作方式。

最佳答案

这是由于@Autowired 行为的一个相当模糊的部分，在3.11.2. @Autowired 中指定。 :

It is also possible to provide all beans of a particular type from the ApplicationContext by adding the annotation to a field or method that expects an array of that type...

The same applies for typed collections...

换句话说，通过说@Autowired @Qualifier("myList") List<String> ，您实际上是在要求“给我所有类型为 java.lang.String 且具有限定符“myList”的 bean 的列表。

3.11.3. Fine-tuning annotation-based autowiring with qualifiers 中提到了解决方案:

If you intend to express annotation-driven injection by name, do not primarily use @Autowired - even if is technically capable of referring to a bean name through @Qualifier values. Instead, prefer the JSR-250 @Resource annotation which is semantically defined to identify a specific target component by its unique name, with the declared type being irrelevant for the matching process.

As a specific consequence of this semantic difference, beans which are themselves defined as a collection or map type cannot be injected via @Autowired since type matching is not properly applicable to them. Use @Resource for such beans, referring to the specific collection/map bean by unique name.

所以在你的测试中使用它，它工作正常:

@Resource(name="myList") private List<String> stringList;

关于java - 使用 util 模式自动连接列表会产生 NoSuchBeanDefinitionException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/1363310/