使用util模式自动连接List会产生NoSuchBeanDefinitionException

问题描述

我有一个bean，我想使用Spring util命名空间注入一个命名列表< util：list id =myList> 但Spring正在寻找而是String类型的bean的集合。我的破解测试是：

I have a bean that i want to inject with a named list using Spring util namespace <util:list id="myList"> but Spring is looking for a collection of beans of type String instead. My broken test is:

@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>

但我得到了

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)

令我困惑的是因为我认为这将是预期的方式。

Which puzzles me rather as I figured this would be the way it was expected to work.

推荐答案

这是由于@Autowired的一个相当模糊的部分行为，在：

This is due to a rather obscure part of @Autowired's behaviour, specified in 3.11.2. @Autowired:

同样适用于打印的集合...

The same applies for typed collections...

换句话说，通过说 @Autowired @Qualifier（myList）List< String> ，你实际上要求给我所有类型 bean的列表java.lang.String 具有限定符myList。

In other words, by saying @Autowired @Qualifier("myList") List<String>, you're actually asking for "give me the list of all beans of type java.lang.String that have the qualifier "myList".

解决方案在：

作为此$ b $的特定结果b语义差异，
自己定义为集合或
地图类型的bean不能通过
@Autowired 注入，因为类型匹配是不是
适用于它们。对于这样的bean使用
@Resource ，引用
特定的集合/映射bean
唯一名称。

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，它运行正常：

So use this in your test, and it works fine:

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

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