java - Spring 的 JavaConfig 和 CustomScopeConfigurer 问题

Question

我看到了一些奇怪的行为，我希望这里有人能对这个问题有所了解。

让我从描述我的设置开始。一、简单的数据对象

public class Apple {
    private String name;
    public Apple withName(String name) {
        this.name = name;
        return this;
    }
    public String getName() {
        return name;
    }
}

还有一个测试类..

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes={TestConfig.class})
public class AppleTest {
    @Autowired private Apple apples;

    @Test
    public void simpleTest() {
        System.out.println("OBJ: "+apples);
    }
}

配置如下

@Configuration
public interface ConfigInterface {
    public Apple getApple();
}

有一个实现类

@Configuration
@Import(AbstractTestConfig.class)
public class TestConfig implements ConfigInterface {
    public Apple getApple() {
        return new Apple().withName("Granny apples");
    }
}

带有配置依赖...

@Configuration
public class AbstractTestConfig {
    @Autowired ConfigInterface conf;

    @Bean Apple myTestApple() {
        return conf.getApple();
    }
}

所有这些都很好用。我运行测试，我看到了我期望的输出。但随后我将 Spanner 扔进方向盘并修改 AbstractTestConfig 如下所示。

@Configuration
public class AbstractTestConfig {
    @Autowired ConfigInterface conf;

    @Bean Apple myTestApple() {
        return conf.getApple();
    }

    // NEW CODE
    @Bean CustomScopeConfigurer scopeConfigurer() {
        return new CustomScopeConfigurer();
    }
}

当需要构造 Apple bean 时，@Autowired 对象 conf 突然为空。

更奇怪的是，如果我将 CustomScopeConfigurer bean 移动到 TestConfig 类，那么它就可以工作了。

我对范围或 CustomScopeConfigurer 对象有什么不了解的地方吗？

Answer 1

复制自 Spring @Bean javadoc :

BeanFactoryPostProcessor-returning @Bean methods

Special consideration must be taken for @Bean methods that return Spring BeanFactoryPostProcessor (BFPP) types. Because BFPP objects must be instantiated very early in the container lifecycle, they can interfere with processing of annotations such as @Autowired, @Value, and @PostConstruct within @Configuration classes. To avoid these lifecycle issues, mark BFPP-returning @Bean methods as static. For example:

@Bean
 public static PropertyPlaceholderConfigurer ppc() {
     // instantiate, configure and return ppc ...
 }

By marking this method as static, it can be invoked without causing instantiation of its declaring @Configuration class, thus avoiding the above-mentioned lifecycle conflicts. Note however that static @Bean methods will not be enhanced for scoping and AOP semantics as mentioned above. This works out in BFPP cases, as they are not typically referenced by other @Bean methods. As a reminder, a WARN-level log message will be issued for any non-static @Bean methods having a return type assignable to BeanFactoryPostProcessor.