Spring Boot 核心特性之组件自动装配

框架Springboot

摘要: Spring Boot 核心特性之组件自动装配

正文:

Spring Boot 核心特性之组件自动装配

Spring Framework 手动装配

模式注解装配

  • ex：@Component、@Service、@Configuration…
  • 装配方式：<context:componet-scan>或@ComponentScan

@Component是一种由Spring 容器托管的通用模式组件

Spring Framework 注解 场景 version
@Repository 数据仓储模式注解 2.0
@Component 通用组件模式注解 2.5
@Service 服务模式注解 2.5
@Controller Web 控制器模式注解 2.5
@Configuration 配置类模式注解 3.0
  • 自定义模式注解

“派生性”(“基注解”<”派生注解”)，可以参考以上注解实现自定义注解：

@Component<@Repository<CustomRepository

@Enable 模块装配

Spring Framework从3.1开始支持@Enable 模块驱动 ，模块是指具备相同领域的功能组件集合组合成为一个独立的单元

举例：

@Enable 注解模块 模块说明
@EnableWebMvc Web MVC模块
@EnableAsync 异步处理模块
@EnableAutoConfiguration 自动配置模块
@EnableEurekaClient Eureka Client模块

  • 注解驱动方式

    version：3.0

    举例：

    org.springframework.web.servlet.config.annotation.EnableWebMvc

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    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Documented
    @Import(DelegatingWebMvcConfiguration.class)
    public @interface EnableWebMvc {}

    org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration

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    @Configuration
    public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {}

  • 接口编程方式

    version：3.1

    举例：

    org.springframework.boot.autoconfigure.EnableAutoConfiguration

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    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Import(EnableAutoConfigurationImportSelector.class)
    public @interface EnableAutoConfiguration {}

    org.springframework.boot.autoconfigure.EnableAutoConfigurationImportSelector

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    public class EnableAutoConfigurationImportSelector
      extends AutoConfigurationImportSelector {}

    public class AutoConfigurationImportSelector
    		implements DeferredImportSelector, BeanClassLoaderAware, ResourceLoaderAware,
    BeanFactoryAware, EnvironmentAware, Ordered {
      @Override
    	public String[] selectImports(AnnotationMetadata annotationMetadata) {}
    }

条件装配

Spring Framework从3.1开始支持在Bean 装配时增加前置条件判断

  • @Profile 配置化方式条件装配

    version：3.1

    举例：

    • class
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    @Configuration
    @Profile("development")
    public class StandaloneDataConfig {

        @Bean
        public DataSource dataSource() {}
    }

    @Configuration
    @Profile("production")
    public class JndiDataConfig {

        @Bean
        public DataSource dataSource() throws Exception {}
    }
    • method
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    @Configuration
    public class SomeConfig {

        @Bean("dataSource")
        @Profile("development")
        public DataSource standaloneDataSource() {}

        @Bean("dataSource")
        @Profile("production")
        public DataSource jndiDataSource() throws Exception {}
    }
    • 激活
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    AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
    ctx.getEnvironment().setActiveProfiles("development");
    ctx.register(SomeConfig.class, StandaloneDataConfig.class, JndiDataConfig.class);
    ctx.refresh();

  • @Conditional 编程方式条件装配

    version：4.0

    举例：

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    @Target({ ElementType.TYPE, ElementType.METHOD })
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Conditional(OnClassCondition.class)
    public @interface ConditionalOnClass {}

    Spring-Boot的@Conditional：

    • ConditionalOnBean
    • ConditionalOnMissingBean
    • ConditionalOnClass
    • ConditionalOnMissingClass
    • ConditionalOnProperty
    • ConditionalOnJava
    • ConditionalOnWebApplication

Spring Boot 自动装配

  • 激活：@EnableAutoConfiguration

    Spring Boot 默认没有激活自动装配，存在@SpringBootApplication注解中

    参考:org.springframework.boot.autoconfigure.AutoConfigurationImport

    Selector#getCandidateConfigurations

  • 配置：/META-INF/spring.factories

    规约文件，META-INFO指的是元信息目录，如spring.handlers、spring.schemas等

    参考:org.springframework.core.io.support.SpringFactoriesLoader

  • 实现：XxxAutoConfiguration

    ex: org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration

Demo-Spring-Boot-Starter

Demo-Spring-Boot-Starter

源码分析

ImportSelector部分

org.springframework.boot.autoconfigure.AutoConfigurationImportSelector#selectImports

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@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		if (!isEnabled(annotationMetadata)) {
			return NO_IMPORTS;
		}
		try {
          	//加载spring-boot-autoconfigure-1.5.6.RELEASE.jar!\META-INF\spring-autoconfigure-metadata.properties
			AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
					.loadMetadata(this.beanClassLoader);
          	 //获取EnableAutoConfiguration里的exclude和excludeName-->LinkedHashMap-->AnnotationAttributes
			AnnotationAttributes attributes = getAttributes(annotationMetadata);
             //获取依赖里所有的xx.jar!\META-INF\spring.factories的value
			List<String> configurations = getCandidateConfigurations(annotationMetadata,
					attributes);
             //利用Set去重
			configurations = removeDuplicates(configurations);
             //排序->先按照字母排序->再按照Order排序(ex:MessageSourceAutoConfiguration#@AutoConfigureOrder)->然后根据@AutoConfigureBefore @AutoConfigureAfter(ex:WebSocketAutoConfiguration#@AutoConfigureBefore)排序
			configurations = sort(configurations, autoConfigurationMetadata);
             //对attributes封装与去重得到exclusions
			Set<String> exclusions = getExclusions(annotationMetadata, attributes);
			checkExcludedClasses(configurations, exclusions);
             //去掉exclusions里的XxAutoConf...
			configurations.removeAll(exclusions);
             //加载过滤器，对不满足ex:默认有一个OnClassCondition(org.springframework.boot.autoconfigure.AutoConfigurationImportSelector#getAutoConfigurationImportFilters()，见下图)的会排除掉()
			configurations = filter(configurations, autoConfigurationMetadata);
			fireAutoConfigurationImportEvents(configurations, exclusions);
			return configurations.toArray(new String[configurations.size()]);
		}
		catch (IOException ex) {
			throw new IllegalStateException(ex);
		}
	}

importFilter

调用ImportSelector部分

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org.springframework.context.support.PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors

org.springframework.context.annotation.ConfigurationClassPostProcessor#postProcessBeanDefinitionRegistry

org.springframework.context.annotation.ConfigurationClassPostProcessor#processConfigBeanDefinitions

org.springframework.context.annotation.ConfigurationClassParser#parse(java.util.Set<org.springframework.beans.factory.config.BeanDefinitionHolder>)

org.springframework.context.annotation.ConfigurationClassParser#processDeferredImportSelectors

String[] imports = deferredImport.getImportSelector().selectImports(configClass.getMetadata());
processImports(configClass, asSourceClass(configClass), asSourceClasses(imports), false);