@SpringBootApplication理解

妖狐艹你老母 2022-06-16 00:25 291阅读 0赞

`@SpringBootApplication`是Spring Boot 的核心注解，它是一个组合注解，源码如下：

@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 {
    
        /** * Exclude specific auto-configuration classes such that they will never be applied. * @return the classes to exclude */
        @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "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 */
        @AliasFor(annotation = EnableAutoConfiguration.class, attribute = "excludeName")
        String[] excludeName() default {};
    
        /** * Base packages to scan for annotated components. Use { @link #scanBasePackageClasses} * for a type-safe alternative to String-based package names. * @return base packages to scan * @since 1.3.0 */
        @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")
        String[] scanBasePackages() default {};
    
        /** * Type-safe alternative to { @link #scanBasePackages} for specifying the packages to * scan for annotated components. The package of each class specified will be scanned. * <p> * Consider creating a special no-op marker class or interface in each package that * serves no purpose other than being referenced by this attribute. * @return base packages to scan * @since 1.3.0 */
        @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")
        Class<?>[] scanBasePackageClasses() default {};
    
    }

这里有两个作用

1.  自动依赖，就像图中所示的，  
    ![这里写图片描述][SouthEast]  
    可以看到只使引入了一个web，但是它会自动为我们引入starter和tomcat等内容，这就是@EnableAutoConfiguration所起的作用
2.  自动扫描@SpringBootApplication所在类的同级包，如图所示：  
    ![这里写图片描述][SouthEast 1]  
    Ch523Application类使Spring Boot的一个入口类，里面有@SpringBootApplication注解，有一个main方法，这个方法就是普通的java main方法，和这个类同级别的包都可以自动的扫描，但是不在这个包里的类就不会扫描到，就像这个图片中的com.wisely.test这个包，这里的类就不会被扫描到spring的容器中。

[SouthEast]: /images/20220616/d4d1305c5b824527b4853f63044594fa.png
[SouthEast 1]: /images/20220616/9ac6679be5264b35bd5e1c0c67bdbd2f.png