禁用 Spring @Autowired Provider<T> 行为

Question

我的 Spring 上下文中有一个 Provider<Foo> 类型的 bean。我想@Autowire 那个 bean 进入另一个类。

@Autowired
private Provider<Foo> fooProvider;

但是，Spring 看到了这一点，并决定我必须在我的上下文中定义了一个 Foo 类型的 bean，并且我希望将它包装在 Provider 中，以便 Spring 可以管理它的范围。

这不是我想要的；我没有Foo，我有Provider<Foo>。春天抱怨：

org.springframework.beans.factory.NoSuchBeanDefinitionException: 没有为依赖项找到类型为 [my.package.Foo] 的匹配 bean：预计至少有 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.Autowired(required=true)}

如何让 Spring 不那么聪明，只自动装配我想要的类型？

更新

感谢您的提问。我创建了一个测试用例来说明我的问题：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration("classpath:foo-context.xml")
@TestExecutionListeners({
        DependencyInjectionTestExecutionListener.class
})
public class FooProviderTest {

    @Autowired
    private javax.inject.Provider<Foo> fooProvider;

    @Test
    public void verifyFooProviderAutowired() {
        assertEquals("foo", fooProvider.get().getFooName());
    }
}

class Foo {
    public String getFooName() {
        return "foo";
    }
}

class SimpleFooProvider implements javax.inject.Provider<Foo> {

    @Override
    public Foo get() {
        return new Foo();
    }

}

foo-context.xml文件如下：

<?xml version="1.0" encoding="UTF-8"?>
<beans
        xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xmlns:context="http://www.springframework.org/schema/context"
        xsi:schemaLocation="
            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
            http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
        ">
    <context:annotation-config/>

    <bean id="fooProvider" class="example.SimpleFooProvider"/>
</beans>

测试的输出：

org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [example.Foo] found for dependency: expected at least 1 bean which qualifies as   autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:947)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:816)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory$DependencyObjectFactory.getObject(DefaultListableBeanFactory.java:1035)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory$DependencyProvider.get(DefaultListableBeanFactory.java:1051)
    at example.FooProviderTest.verifyFooProviderAutowired(FooProviderTest.java:28)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
    at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
    at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
    at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:74)
    at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:202)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:65)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

请注意，测试不会在断言上失败；它无法初始化应用程序上下文。

奇怪的是，将测试字段的声明类型从 Provider<Foo> 显式更改为 SimpleFooProvider 会导致测试通过而没有任何抱怨。也就是说，

@Autowired
private SimpleFooProvider fooProvider;

Answer 1

假设Provider 是javax.inject.Provider，Spring 会自动将Provider 实现自动装配到该字段中

@Autowired
private Provider<Foo> fooProvider;

例如，这是通过以下调用层次结构完成的

AutowiredAnnotationBeanPostProcessor#inject(Object bean, String beanName, PropertyValues pvs)
DefaultListableBeanFactory#resolveDependency(DependencyDescriptor descriptor, String beanName,Set<String> autowiredBeanNames, TypeConverter typeConverter)
DependencyProviderFactory#createDependencyProvider(DependencyDescriptor descriptor, String beanName)

创建一个DependencyProvider 对象，实现为

private class DependencyProvider extends DependencyObjectFactory implements Provider<Object> {

    public DependencyProvider(DependencyDescriptor descriptor, String beanName) {
        super(descriptor, beanName);
    }

    @Override
    public Object get() throws BeansException {
        return getObject();
    }
}

其中getObject() 从封闭的DefaultListableBeanFactory 实例中获取bean。

所以，如果有的话，你可能会在尝试调用时遇到异常

fooProvider.get();

因为它试图从上下文中获取Foo bean，但找不到。