java - 名称依赖注入(inject)如何在 Spring @Bean 方法参数中工作

Question

我了解 Spring DI 及其一般工作原理。

但我在这里无法理解的是在 @Bean 方法参数注入(inject)的情况下，spring 如何知道参数名称以便它可以根据参数名称从其 bean 工厂注入(inject) bean？

例如，在下面的示例中，方法 fernas1 和 fernas2 参数在运行时被删除。但是，spring 仍然可以将正确的 Abbas bean 实例注入(inject)其中。

@SpringBootApplication
public class DemoApplication {

    @Autowired
    private Abbas abbas1;    // this is understandable, hence the field name is available at runtime

    @Autowired
    private Abbas abbas2;   // this is understandable, hence the field name is available at runtime

    public static void main(String[] args) {
        ConfigurableApplicationContext ctx = SpringApplication.run(DemoApplication.class, args);

        Map<String, Fernas> beansOfType = ctx.getBeansOfType(Fernas.class);
        System.out.println(beansOfType);

        Arrays.stream(DemoApplication.class.getMethods())
                .filter(m -> m.getName().startsWith("fernas"))
                .flatMap(m -> Stream.of(m.getParameters()))
                .map(Parameter::getName)
                .forEach(System.out::println);

        System.out.println(ctx.getBean(DemoApplication.class).abbas1);
        System.out.println(ctx.getBean(DemoApplication.class).abbas2);
    }

    class Abbas {
        String name;

        @Override
        public String toString() {
            return name;
        }
    }

    class Fernas {
        Abbas abbas;

        @Override
        public String toString() {
            return abbas.toString();
        }
    }

    @Bean
    public Abbas abbas1() {
        Abbas abbas = new Abbas();
        abbas.name = "abbas1";
        return abbas;
    }

    @Bean
    public Abbas abbas2() {
        Abbas abbas = new Abbas();
        abbas.name = "abbas2";
        return abbas;
    }

    // this is not understandable, hence the parameter name is NOT available at runtime
    @Bean
    public Fernas fernas1(Abbas abbas1) {
        Fernas fernas1 = new Fernas();
        fernas1.abbas = abbas1;
        return fernas1;
    }

    // this is not understandable, hence the parameter name is NOT available at runtime
    @Bean
    public Fernas fernas2(Abbas abbas2) {
        Fernas fernas2 = new Fernas();
        fernas2.abbas = abbas2;
        return fernas2;
    }
}

编辑:同样的问题和@Javier 的解决方案都适用于method 和constructor 参数。

Answer 1

如果参数名称反射不可用，它将使用类文件本身中的信息。参见 DefaultParameterNameDiscoverer

Default implementation of the ParameterNameDiscoverer strategy interface, using the Java 8 standard reflection mechanism (if available), and falling back to the ASM-based LocalVariableTableParameterNameDiscoverer for checking debug information in the class file.

例如DemoApplication.fernas2的LocalVariableTable是

    Start  Length  Slot  Name   Signature
        0      16     0  this   Lcom/example/demo/DemoApplication;
        0      16     1 abbas2   Lcom/example/demo/DemoApplication$Abbas;
        9       7     2 fernas2   Lcom/example/demo/DemoApplication$Fernas;