java - 具有运行时确定的构造函数参数的部分 Autowiring Spring 原型(prototype) bean

Question

ConstructorResolver.autowireConstructor(...) 的 javadoc 说

Also applied if explicit constructor argument values are specified, matching all remaining arguments with beans from the bean factory.

但我无法让它工作。我得到一个 BeanCreationException:

Could not resolve matching constructor (hint: specify index/type/name arguments for simple parameters to avoid type ambiguities)

在这个例子中，我有一个带有构造函数的 bean，它采用 Spring beans 以及一个 String 和一个仅在运行时才知道的 int。

@Component
@Scope(BeanDefinition.SCOPE_PROTOTYPE)
public class BeanWithRuntimeDependencies {

    public final DependencyA dependencyA;
    public final DependencyB dependencyB;
    public final String myString;
    public final int myInt;

    public BeanWithRuntimeDependencies(
            DependencyA dependencyA, DependencyB dependencyB, 
            String myString, int myInt) {
        this.dependencyA = dependencyA;
        this.dependencyB = dependencyB;
        this.myString = myString;
        this.myInt = myInt;
    }

}

@Component
public class DependencyA { /* ... */ }

@Component
public class DependencyB { /* ... */ }

和我的测试:

@RunWith(SpringRunner.class)
@SpringBootTest
public class PrototypeBeanConstructorsApplicationTests {

    @Autowired private ApplicationContext context;

    @Autowired private DependencyA dependencyA;

    @Autowired private DependencyB dependencyB;

    @Test
    public void getBeanFromContext() {
        BeanWithRuntimeDependencies bean = 
            context.getBean(BeanWithRuntimeDependencies.class, "runtime string", 10);
        assertNotNull(bean);
        assertEquals(dependencyA, bean.dependencyA);
        assertEquals(dependencyB, bean.dependencyB);
        assertEquals("runtime string", bean.myString);
        assertEquals(10, bean.myInt);
    }

}

ConstructorResolver.autowireConstructor(...)的源码有注释:

// Explicit arguments given -> arguments length must match exactly.

这似乎与其 javadoc 相矛盾。

这有可能吗？我做错了什么？

Answer 1

看起来不可能按照您的方式进行。

其实情况很奇怪。根据 ConstructorResolver.autowireConstructor(...)(源代码行 #207)中的下一个片段，Spring 不会将您的构造函数视为调用的候选对象:

...    
// Explicit arguments given -> arguments length must match exactly.
if (paramTypes.length != explicitArgs.length) {
    continue;
}

正如您正确指出的那样，它确实与 javadoc 声明相矛盾:

...matching all remaining arguments with beans from the bean factory

但是无论如何，实现意味着默认情况下 Spring 无法解析构造函数来实例化此类 bean。而且您必须手动创建工厂方法。像这样的东西:

@Configuration
public class Config{

    @Bean
    @Scope(BeanDefinition.SCOPE_PROTOTYPE)
    public BeanWithRuntimeDependencies beanWithRuntimeDependencies(String myString, int myInt){
        return new BeanWithRuntimeDependencies(dependencyA(), dependencyB(), myString, myInt);
    }

    @Bean
    public DependencyA dependencyA(){
        return new dependencyA();
    }

    @Bean
    public DependencyB dependencyB(){
        return new dependencyB();
    }
}

然后你可以根据需要从上下文中获取bean:

BeanWithRuntimeDependencies bean = 
    context.getBean(BeanWithRuntimeDependencies.class, "runtime string", 10);

---

如果您不想处理配置类和工厂方法，您可以简单地将所需的 bean 传递到 context.getBean() 中。当然，您必须从上下文中获取此 bean:

BeanWithRuntimeDependencies bean = 
    context.getBean(BeanWithRuntimeDependencies.class, 
        context.getBean(DependencyA.class), 
        context.getBean(DependencyB.class),
        "runtime string", 10);