执行流程

spring中Bean对象的执行流程大致分为四步:

启动Spring容器
实例化Bean对象
Bean对象注册到Spring容器中
将Bean对象装配到所需的类中

①启动Spring容器,在main方法中获取spring上下文对象并配备spring.

import demo.*;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;


public class Test {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
    }
}

②实例化Bean对象,spring根据配置文件中的路径搜寻"demo"包中含有注解的类.

通过这些类实例化出Bean对象,并对他们进行初始化Bean对象的属性,

<?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:content="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">
    <content:component-scan base-package="demo"></content:component-scan>
</beans>

③将实例化出的Bean对象注册到Spring容器当中.

@Component
public class UserBean {
    private String name;

    @Bean(name = {"user","wualala"})
    //Bean方法注解,将方法返回的对象存储到spring中变成Bean对象
    public UserBean userBeanMethod(){
        UserBean userBean = new UserBean();
        userBean.name = "wow";
        return userBean;
    }

④Bean对象的使用,将其分配到所需的类中

@Controller
public class UserController {

    @Resource(name = "user1")
    //@Autowired
    private UserBean userBean;

    public UserBean getUserBean() {
        return userBean;
    }
}