- Spring Boot 启动
- 前言
- 一、入口程序
- 二、注解@SpringBootApplication
- 总结
前言
@SpringBootApplication 注解是 Spring Boot 最核心、最基础的注解。加在类上，表示这个类是一个配置类，该类声明一个或多个 @Bean 方法，并且还触发自动配置和组件扫描。等效于@Configuration @EnableAutoConfiguration 和 @ComponentScan 三个注解。
一、入口程序
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
SpringApplication.run(DemoApplication.class, args);
}
}
二、注解@SpringBootApplication
@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 {
}
@SpringbootConfigruation
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@documented
@Configuration
public @interface SpringBootConfiguration {
@AliasFor( // 继承 configuration 这个注解
annotation = Configuration.class
)
boolean proxyBeanMethods() default true;
}
@EnableAutoConfiguration
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@documented
@Inherited
@AutoConfigurationPackage
@import(AutoConfigurationimportSelector.class)
// enable 类型的注解 主要就是用来import 一些配置文件的注解，enable某个组件，便于我们理解
public @interface EnableAutoConfiguration {
String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
Class[] exclude() default {};
String[] excludeName() default {};
}
@ComponentScan
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@documented
@Repeatable(ComponentScans.class)
public @interface ComponentScan {
@AliasFor("basePackages")
String[] value() default {};
@AliasFor("value")
String[] basePackages() default {};
Class[] basePackageClasses() default {};
Class nameGenerator() default BeanNameGenerator.class;
Class scopeResolver() default AnnotationScopemetadataResolver.class;
ScopedProxyMode scopedProxy() default ScopedProxyMode.DEFAULT;
}
浅析SpringApplication的run方法
// 1. 以使用默认设置和用户提供的参数从指定的类运行
public static ConfigurableApplicationContext run(Class[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}
//2. 真正的run 方法
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
DefaultBootstrapContext bootstrapContext = createBootstrapContext();
ConfigurableApplicationContext context = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(bootstrapContext, this.mainApplicationClass);
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
context.setApplicationStartup(this.applicationStartup);
prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, null);
throw new IllegalStateException(ex);
}
return context;
}
总结
@SpringBootApplication 等效于@Configuration @EnableAutoConfiguration 和 @ComponentScan 三个注解，这三个注解分别掌管配置，加载，扫描。流程就是从 ClassPath下扫描所有的 meta-INF/spring.factories 配置文件，并将spring.factories 文件中的 EnableAutoConfiguration 对应的配置项通过反射机制实例化为对应标注了 @Configuration 的形式的IoC容器配置类，然后注入IoC容器。
