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springboot启动类解析

SpringBoot启动类

@SpringBootApplication
public class MySpringbootApplication {
    public static void main(String[] args) {
        SpringApplication.run(MySpringbootApplication.class, args);
    }
}

SpringApplication.run方法源码

/**
 * Static helper that can be used to run a {@link SpringApplication} from the
 * specified source using default settings.
 * @param primarySource the primary source to load
 * @param args the application arguments (usually passed from a Java main method)
 * @return the running {@link ApplicationContext}
 */
public static ConfigurableApplicationContext run(Class<?> primarySource,
        String... args) {
    return run(new Class<?>[] { primarySource }, args);
}

理解:这是一个静态的助手类,可以用于跑一个SpringApplication实例,使用@SpringBootApplication传入一些默认的配置,SpringApplication通过primarySource传入,args需要传入main方法中的一个数组,该方法运行后返回一个运行中的上下文对象ApplicationContext

@SpringBootApplication源码

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration //开启自动配置功能
@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 {}; //排除哪些自动配置类
    @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 {};
}

@ComponentScan:用于扫描,会扫描Application启动类当前目录及其子目录下的所有包类

@SpringBootConfiguration:具有@Configuration注解,是一个用于标识配置类的容器

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
}

@EnableAutoConfiguration:用于开启自动装配功能

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import({AutoConfigurationImportSelector.class})
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
    Class<?>[] exclude() default {};
    String[] excludeName() default {};
}

原文 https://segmentfault.com/a/1190000022036321

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