java 使用 spring-boot @ConditionalOnMissingBean 加载 Spring 配置类的顺序？
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Spring configuration class loading order with spring-boot @ConditionalOnMissingBean?
提问by Gethin James
I'd like to enable custom configuration and sensible defaults using @ConditionalOnMissingBean?
I have a spring boot application:
我想使用@ConditionalOnMissingBean? 我有一个弹簧启动应用程序：
@Configuration
@Import({CustomConfiguration.class, DefaultConfiguration.class})
@EnableAutoConfiguration(exclude={MetricFilterAutoConfiguration.class})
public class Application {
@Autowired
ErrorListener errorListener;
}
and a CustomConfigurationthat allows for either Spring xml or component scanning:
和一个CustomConfiguration允许 Spring xml 或组件扫描：
@Configuration("customConfiguration")
@ImportResource("classpath:customContext.xml")
@ComponentScan({"org.custom.impl"})
public class CustomConfiguration
The DefaultConfigurationuses ConditionalOnMissingBean:
的DefaultConfiguration用途ConditionalOnMissingBean：
@Bean
@ConditionalOnMissingBean
ErrorListener errorListener() {
return new LoggingErrorListener();
}
What I'm trying to achieve is allow for a custom ErrorListenerto be defined in the classpath, if not defined then use the default LoggingErrorListener(via the ConditionalOnMissingBean). I'm finding that the DefaultConfigurationis always being used before the CustomConfiguration.
我想要实现的是允许ErrorListener在类路径中定义自定义，如果未定义则使用默认值LoggingErrorListener（通过ConditionalOnMissingBean）。我发现DefaultConfiguration总是在CustomConfiguration.
I've been experimenting with @DependsOnand @Orderbut no joy.
我一直在尝试@DependsOn和@Order，但没有喜悦。
回答by Dave Syer
I wouldn't use @ConditionalOnMissingBeanoutside of an auto-configuration class if I were you, unless you can control the order of import of @Configurationclasses. Auto-configuration does it explicitly, but normal user config classes (especially if they are @ComponentSCanned) do not have a defined order.
@ConditionalOnMissingBean如果我是你，我不会在自动配置类之外使用，除非你可以控制@Configuration类的导入顺序。自动配置明确地做到了这一点，但普通的用户配置类（特别是如果它们是@ComponentSCanned）没有定义的顺序。
回答by Sanjay
In response to Daves answer: Looks like it works for independent beans which wouldn't interfere with Spring Boot. For example, when developing a library for Spring Boot applications, I wanted to provide a RestTemplateif one is not provided by the the application developer. @ConditionalOnMissingBeanseemed to work:
回应 Daves 的回答：看起来它适用于不会干扰 Spring Boot 的独立 bean。例如，在为 Spring Boot 应用程序开发库时，我想提供一个RestTemplate应用程序开发人员未提供的if 。@ConditionalOnMissingBean似乎工作：
@Bean
@ConditionalOnMissingBean(RestTemplate.class)
public RestTemplate restTemplate() {
return new RestTemplate();
}
To confirm whether it would work consistently, I gave a look at Spring's source code (e.g. see ConditionEvaluator). Seemed that Spring skips creating beans with @ConditionalOnMissingBeanannotations in the first pass. It would then do a second pass to configure these beans.
为了确认它是否能始终如一地工作，我查看了 Spring 的源代码（例如，参见ConditionEvaluator）。似乎 Spring@ConditionalOnMissingBean在第一遍跳过创建带有注释的bean 。然后它会做第二遍来配置这些 bean。
Also, I saw that @ConditionalOnMissingBeanworks well on @Configurationclasses or @Beansinside configuration classes. But it does not work properly elsewhere, e.g. on or inside classes annotated with @Component.
此外，我看到它@ConditionalOnMissingBean在@Configuration类或@Beans配置类内部运行良好。但它在其他地方不能正常工作，例如在用@Component.
