springboot情操陶冶-@SpringBootApplication注解解析

当前位置:首页99平台导航 >

99平台导航

springboot情操陶冶-@SpringBootApplication注解解析

时间:2019-11-14本站浏览次数:183

       

承接前文springboot情操陶冶-@Configuration注解解析,本文将在前文的基础上对@SpringBootApplication注解作下简单的分析

@SpringBootApplication

该注解是springboot最集中的一个注解,也是应用最广泛的注解。官方也多用此注解以启动spring服务,我们看下其中的源码

@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@SpringBootConfiguration@EnableAutoConfiguration@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })public @interface SpringBootApplication { @AliasFor(annotation = EnableAutoConfiguration.class) Class<?>[] exclude() default {}; @AliasFor(annotation = EnableAutoConfiguration.class) String[] excludeName() default {}; @AliasFor(annotation = ComponentScan.class, attribute = "basePackages") String[] scanBasePackages() default {}; @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses") Class<?>[] scanBasePackageClasses() default {};}

通过上述代码可知,其整合了@EnableAutoConfiguration@ComponentScan两个主要的注解,并以此作了默认的指定。

    属性excludeexcludeName,其默认为空,指定的话最终由EnableAutoConfiguration.class来完成解析

    属性scanBasePackagesscanBasePackageClasses,其默认为空,指定的话最终由ComponentScan.class来完成解析

    默认情况下,以@SpringBootApplication注解的所在类的包名作为beanDefinition扫描路径。扫描过程中屏蔽META-INFspring.factories文件中org.springframework.boot.autoconfigure.EnableAutoConfiguration属性指定的class集合

    支持多个@ComponentScan注解同时与@SpringBootApplication注解搭配使用

@ComponentScan注解在前文中已了解的差不多了,笔者此处就针对@EnableAutoConfiguration注解作下详细的分析

@EnableAutoConfiguration

单纯从英文单词上看是开启自动注入的意思,具体的话笔者还是根据源码来解读。首先看下注解的源码

@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@Documented@Inherited@AutoConfigurationPackage@Import(AutoConfigurationImportSelector.class)public @interface EnableAutoConfiguration { String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration"; /** * Exclude specific auto-configuration classes such that they will never be applied. * @return the classes to exclude */ Class<?>[] exclude() default {}; /** * Exclude specific auto-configuration class names such that they will never be * applied. * @return the class names to exclude * @since 1.3.0 */ String[] excludeName() default {};}

它用到了我们前文提及的@Import注解,所以我们关注所引入的AutoConfigurationImportSelector.class

AutoConfigurationImportSelector

其是DeferredImportSelector.class接口的实现类,此处我们直接查看复写的方法selectImports()

@Override public String[] selectImports(AnnotationMetadata annotationMetadata) { // spring.boot.enableautoconfiguration属性读取,默认为true if (!isEnabled(annotationMetadata)) { return NO_IMPORTS; } // read all META-INFspring-autoconfigure-metadata.properties files AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader .loadMetadata(this.beanClassLoader); // 获取相应类上@EnableAutoConfiguration对应的属性 AnnotationAttributes attributes = getAttributes(annotationMetadata); // read all <org.springframework.boot.autoconfigure.EnableAutoConfiguration> properties from META-INFspring.factories List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes); configurations = removeDuplicates(configurations); // read exclude/excludeName property or spring.autoconfigure.exclude property Set<String> exclusions = getExclusions(annotationMetadata, attributes); // make sure the assignable exclusions are present in classpath and in configurations collection, or will throw exception checkExcludedClasses(configurations, exclusions); configurations.removeAll(exclusions); // filter the present configurations configurations = filter(configurations, autoConfigurationMetadata); // fire the AutoConfigurationImportEvent by AutoConfigurationImportListener.class fireAutoConfigurationImportEvents(configurations, exclusions); return StringUtils.toStringArray(configurations); }

对上述的步骤此处再作下总结

    优先判断环境变量spring.boot.enableautoconfiguration,如果指定为false,则不引入任何类。默认为true

    读取classpath环境下所有的META-INFspring-autoconfigure-metadata.properties文件,加载其中的所有属性保存至autoConfigurationMetadata

    获取相应类上@EnableAutoConfiguration对应的属性,其实也就是exclude属性和excludeName属性

    读取classpath环境下所有的META-INFspring.factories文件中的org.springframework.boot.autoconfigure.EnableAutoConfiguration属性,得到configurations集合

    根据第三步读取的配置以及spring.autoconfigure.exclude环境变量指定的配置,得到exclusions集合

    确保exclusions集合是configurations集合的子集,以及exclusions集合内的class均是存在于classpath环境的。否则异常会抛出

    根据上述的exclusions集合筛选出未被过滤的configurations集合。

    根据第7点筛选出来的configurations集合,再在autoConfigurationMetadata的基础上针对ConditionalOnClass属性筛选一轮比如:org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration.ConditionalOnClass=org.springframework.cache.CacheManager表示如果要应用CacheAutoConfiguration,则得保证org.springframework.cache.CacheManager类存在

    触发AutoConfigurationImportEvent事件

    返回筛选过后的configurations集合

笔者此处罗列下spring-boot-autoconfigure-2.0.3.REALEASE包中的spring.factories中的EnableAutoConfiguration默认属性,属性太多,节选如下

# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,...org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,...org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,...org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

当然用户也可以自定义去实现需要自动注入的配置类。

总结

@SpringBootApplication注解内含@EnableAutoConfiguration注解和@ComponentScan注解,所以这两个注解结合再搭配上@Configuration注解便可以实现springboot的相关功能了。在这之中,@EnableAutoConfiguration注解最为重要,其扩展性很好,方便springboot无缝对接不同的插件(NoSql插件、Web插件、JMX协议插件等等),读者需要好好分析。

下节预告

通过查阅上述的多个自动注解,发现用到了@ConditionalAutoConfigureAfter注解,都属于条件判断,在深入理解springboot整合其他插件前,必须对此两个注解有深刻的理解。




公司地址:天津市北辰区双街新城双新大道145号
联系人:刘春娟 15829214720
高洪伟 13566773288
电话:18518816519 传真:zi4256ad@hotmail.com
邮箱:zv4qhpow1@sohu.com

粤公网安备 44030702001579号

99最新导航@