@Configuration注解

作用一：@Configuration配置spring 并 启动spring容器

spring容器配置类

@Configuration
public class SpringConfig {
    public SpringConfig(){
        System.err.println("SpringConfig启动");
    }
}

主线程启动类

@SpringBootApplication
public class Demo2Application {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationConfigApplicationContext =
                new AnnotationConfigApplicationContext(SpringConfig.class);
        System.err.println("服务启动成功");
    }

}

结果

可以看出我们在主程序里面启动了spring容器，@Configuration配置SpringConfig并启动Spring容器

作用二：@Configuration启动容器+@Bean注册Bean，@Bean下管理bean的生命周期

启动类

@SpringBootApplication
public class Demo2Application {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationConfigApplicationContext =
                new AnnotationConfigApplicationContext(SpringConfig.class);
        System.err.println("服务启动成功");
        User getUser = annotationConfigApplicationContext.getBean("getUser", User.class);
        System.err.println(getUser);
    }

}

实体类

public class User {
    @Value("yyb")
    private String name;
    @Value("nan")
    private String sex;
    @Value("15")
    private Integer age;

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
    }
}

spring容器配置类 并在里面注册bean

@Configuration
@ComponentScan("com.yun.demo2.pojo")
public class SpringConfig {
    public SpringConfig(){
        System.err.println("SpringConfig启动");
    }
    @Bean
    public User getUser(){
        return new User();
    }
}

结果

可以看出注册bean成功：用@Bean注解时方法名相当于 bean的id 返回值是bean的class

作用三：@Configuration启动容器+@Component注册Bean

启动类

@SpringBootApplication
public class Demo2Application {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext annotationConfigApplicationContext =
                new AnnotationConfigApplicationContext(SpringConfig.class);
        System.err.println("服务启动成功");
        User getUser = annotationConfigApplicationContext.getBean("user", User.class);
        System.err.println(getUser);
    }

}

实体类并用@component注册bean

@Component
public class User {
    @Value("yyb")
    private String name;
    @Value("nan")
    private String sex;
    @Value("15")
    private Integer age;

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", sex='" + sex + '\'' +
                ", age=" + age +
                '}';
    }
}

spring配置类

@Configuration
@ComponentScan("com.yun.demo2.pojo")
public class SpringConfig {
    public SpringConfig(){
        System.err.println("SpringConfig启动");
    }
}

结果

可以看出注册bean成功，当使用@component注解时，类名小写相当于bean的id 同时类名也表示实体类名 所有类名也是bean的class