简介

@SpringBootConfiguration继承自@Configuration，二者功能也一致，标注当前类是配置类，并会将当前类内声明的一个或多个以@Bean注解标记的方法的实例纳入到spring容器中，并且实例名就是方法名。

@SpringBootConfiguration

@Target({ElementType.TYPE}) 	//表明注解的作用目标是接口、类、枚举
@Retention(RetentionPolicy.RUNTIME) 	// 表示注解会在class字节码文件中存在，在运行时可以通过反射获取到
@Documented 	//说明该注解将被包含在javadoc中
@Configuration	//spring 注解，用于定义配置类，可替换xml配置文件，被注解的类内部包含有一个或多个被@Bean注解的方法，这些方法将会被AnnotationConfigApplicationContext或AnnotationConfigWebApplicationContext类进行扫描，并用于构建bean定义，初始化Spring容器
public @interface SpringBootConfiguration {
    @AliasFor(
        annotation = Configuration.class
    )
    boolean proxyBeanMethods() default true;
}

SpringBootConfiguration VS Configuration

SpringBootConfiguration ：

标注这个类是一个配置类；
它只是@Configuration注解的派生注解；
它与@Configuration注解的功能一致；
只不过@SpringBootConfiguration是springboot的注解，而@Configuration是spring的注解。

@SpringBootConfiguration
public class DemoConfig {

    @Bean // 依赖关系
    public Map createMap(){
        Map map = new HashMap();
        System.out.println("创建map");
        map.put("username","zhoupeng");
        map.put("age",24);
        return map;
    }

    @Bean
    public Student student() {
        Student std = new Student();
        System.out.println("创建Student");
        std.setName("zhoupeng");
        std.setClazz("2020");
        return std;
    }

    @Bean
    public Teacher teacher() {
        Teacher tec = new Teacher();
        System.out.println("创建Teacher");
        tec.setName("Teacher Zhang");
        tec.setMajoringSubject("mathematics");
        return tec;
    }
}

@Configuration

可以理解为一个Configuration就是对应的一个Spring的xml版的容器；一个被@Configuration标注的类,相当于一个applicationContext.xml文件
@Component、@Bean是两种使用注解来定义bean的方式。
@Component（和@Service和@Repository）用于自动检测和使用类路径扫描自动配置bean。注释类和bean之间存在隐式的一对一映射（即每个类一个bean）。
@Bean用于显式声明单个bean，而不是让Spring像上面那样自动执行它。它将bean的声明与类定义分离，并允许您精确地创建和配置bean。
@Bean则常和@Configuration注解搭配使用：		

@Configuration
public class DemoConfig {

    @Bean
    public Map createMap(){
        Map map = new HashMap();
        System.out.println("创建map");
        map.put("username","zhoupeng");
        map.put("age",24);
        return map;
    }

    @Bean
    public Student student() {
        Student std = new Student();
        System.out.println("创建Student");
        std.setName("zhoupeng");
        std.setClazz("2020");
        return std;
    }

    @Bean
    public Teacher teacher() {
        Teacher tec = new Teacher();
        System.out.println("创建Teacher");
        tec.setName("Teacher Zhang");
        tec.setMajoringSubject("mathematics");
        return tec;
    }
}		

都可以使用@Autowired或者@Resource注解注入；
@Bean注解告诉Spring这个方法将会返回一个对象，这个对象要注册为Spring应用上下文中的bean。通常方法体中包含了最终产生bean实例的逻辑。
两者的区别：
	如果想将第三方的类变成组件，没有源代码，也就没办法使用@Component进行自动配置，这种时候使用@Bean就比较合适了。		
	另外@Bean注解的方法返回值是对象，可以在方法中为对象设置属性。

SpringBootConfiguration VS SpringBootApplication

SpringBootApplication注解包含了SpringBootConfiguration 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 {}

直接在SpringBootApplication注解作用的类上来注册一个Bean

@SpringBootApplication(exclude={DataSourceAutoConfiguration.class})
public class App {
    @Bean
    public Teacher teach() {
        Teacher tec = new Teacher();
        System.out.println("Creating Teacher use SpringBootApplication");
        tec.setName("Teacher Bai");
        tec.setMajoringSubject("English");
        return tec;
    }

    public static void main(String[] args) {
        System.out.println( "Hello SpringBoot!" );
        ConfigurableApplicationContext context = SpringApplication.run(App.class, args);
        Map map = (Map) context.getBean("createMap");   //注意这里直接获取到这个方法bean
        int age = (int) map.get("age");
        System.out.println("age=="+age);
        Student std = (Student) context.getBean("student");
        System.out.println(String.format("%s is a student in class NO.%s", std.getName(), std.getClazz()));
        Teacher tec = (Teacher) context.getBean("teacher");
        System.out.println(String.format("%s majored in %s", tec.getName(), tec.getMajoringSubject()));
        Teacher teach = (Teacher) context.getBean("teach");
        System.out.println(String.format("%s majored in %s", teach.getName(), teach.getMajoringSubject()));
    }
}

运行效果

Hello SpringBoot！
2020-08-04 12:42:21.659  INFO 8808 --- [           main] com.zpnlp.demo.App                       : Starting App using Java 14.0.2 on DESKTOP-BKDE1EB with PID 8808 (F:\code\java\spring-boot\target\classes started by 17888 in F:\code\java\spring-boot)
2020-08-04 12:42:21.660  INFO 8808 --- [           main] com.zpnlp.demo.App                       : No active profile set, falling back to default profiles: default
2020-08-04 12:42:22.247  INFO 8808 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-08-04 12:42:22.252  INFO 8808 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-08-04 12:42:22.252  INFO 8808 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.36]
2020-08-04 12:42:22.328  INFO 8808 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-08-04 12:42:22.328  INFO 8808 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 643 ms
创建map
创建Student
创建Teacher
Creating Teacher use SpringBootApplication
2020-08-04 12:42:22.505  INFO 8808 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2020-08-04 12:42:22.546  INFO 8808 --- [           main] o.s.b.a.w.s.WelcomePageHandlerMapping    : Adding welcome page template: index
2020-08-04 12:42:22.678  INFO 8808 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-08-04 12:42:22.685  INFO 8808 --- [           main] com.zpnlp.demo.App                       : Started App in 1.216 seconds (JVM running for 1.593)
age==24
zhoupeng is a student in class NO.2020
Teacher Zhang majored in mathematics
Teacher Bai majored in English

文章推荐

1. SpringBootConfiguration
2. springbootconfiguration-annotation
3. Spring核心注解
4. 知乎专栏-SpringBoot 配置类解析

注：

1. 代码中的实体需自行创建，如：Student、Teacher等
2. 当前demo涉及版本：jdk8 spring-boot 2.4.0
3. 部分文章为国外网站博客，建议使用科学上网进行查阅