[spring-context]------@Configuration

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本文深入探讨了Spring框架中@Configuration注解的起源及其四种启动方式，包括直接注册到ApplicationContext、XML配置、context:component-scan扫描及与@ComponentScan结合替代XML配置。通过实例代码展示了如何用Java代码替代传统XML配置，实现更简洁的Spring Bean管理。

@Configuration的由来

@Configuration是在Spring3.0之后出现的，其目的是为了简化原有的spring的xml配置。结合@Bean注解，实现了用Java代码的方式来管理spring-bean

@Configuration类的启动方式

第一种方式：将@Configuration类注册到AnnotationConfigApplicationContext中

AppConfig

@Configuration
public class AppConfig {

    @Bean
    public MySpringBean mySpringBean() {
        System.out.println("注册mySpringBean");
        MySpringBean mySpringBean = new MySpringBean();
        mySpringBean.setName("mySpringBeann");
        return mySpringBean;
    }
}

AppMainMethodOne

public class AppMainMethodOne {

    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        MySpringBean mySpringBean = (MySpringBean) context.getBean("mySpringBean");
        System.out.println(mySpringBean);
    }
}

第二种方式：将@Configuration类当作普通的spring-bean，在xml文件中配置（其实这种方式有点本末倒置）

AppConfig

public class AppConfig {
    @Bean
    public MySpringBean mySpringBean() {
        System.out.println("注册mySpringBean");
        MySpringBean mySpringBean = new MySpringBean();
        mySpringBean.setName("mySpringBeann");
        return mySpringBean;
    }
}

configuration.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

    <context:annotation-config/>

    <bean id="appConfig" class="org.hugh.spring.configuration.AppConfig"/>

</beans>

AppMainMethodTwo

public class AppMainMethodTwo {

    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:configuration.xml");
        MySpringBean mySpringBean = (MySpringBean) applicationContext.getBean("mySpringBean");
        System.out.println(mySpringBean);
    }
}

第三种方式：使用context:component-scan，（和二种方式一样，也是本末倒置）

修改configuration.xml即可
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">

    <!--用于激活BeanPostProcessor-->
    <context:annotation-config/>
    <!-- identical with @ComponentScan-->
    <context:component-scan base-package="org.hugh.spring.configuration"/>

</beans>

第四种方式：@Configuration和@ComponentScan结合，替换xml配置文件

AppScanConfig
@Configuration
@ComponentScan("org.hugh.spring.bean")
public class AppScanConfig {
}

org.hugh.spring.bean.User

@Component
@Data
public class User implements Serializable {

    private static final long serialVersionUID = 5135661460008089536L;

    private String userName = "Jack";

    private Integer age = 18;
}

AppMainMethodFour

public class AppMainMethodFour {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppScanConfig.class);
        User user = (User) context.getBean("user");
        System.out.println(user);
    }
}