1、原因

不知不觉已经从事java开发好几年了，成了人们口中的老司机。但是一直都是恍恍惚惚过来，对于框架底层实现一直都没有怎么了解过，只是在面试的时候背些面试题。慢慢地发现不能这样，需要振作，笑~~~~。从这篇开始，记录自己对于Spring加载过程的源码查看。

2、开始

1、在Spring加载bean并获取bean定义的常用类是ClassPathXmlApplicationContext 以及AnnotationConfigApplicationContext。ClassPathXmlApplicationContext用来读取并加载默认classpath 路径下面的配置文件，AnnotationConfigApplicationContext是加载注解@Configuration标注的配置类。我现在关注于ClassPathXmlApplicationContext。

2、新建一个maven项目，并引入spring相关jar包。

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <!-- 排除自带logging，引入log4j2 -->
                <exclusion>
                    <groupId>org.springframework.boot</groupId>
                    <artifactId>spring-boot-starter-logging</artifactId>
                </exclusion>
                <!-- 排除自带logging，引入log4j2 -->
            </exclusions>
        </dependency>

spring-boot-starter-we会依赖引入spring-context包，定义接口以及实现类

public interface Person {

    void say();
}

@Log4j2
public class Teacher implements Person {

    @Override
    public void say() {
        log.info("开始上课!");
    }
}

编写bean.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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="person" class="service.impl.Teacher"/>
</beans>

开始编写测试类用来测试bean加载过程：

    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("bean.xml");
        Teacher teacher = (Teacher) applicationContext.getBean("person");
        teacher.say();

    }

第一行打上断点，debug开始跟着走，就会来到：

    public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) throws BeansException {
        super(parent);
        this.setConfigLocations(configLocations);
        if (refresh) {
            this.refresh();
        }

    }        

点击this.refresh()方法进入就来到了最核心的地方，这里弄懂了，bean加载就弄懂了：

public void refresh() throws BeansException, IllegalStateException {
        synchronized(this.startupShutdownMonitor) {
            StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");
            this.prepareRefresh();
            ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
            this.prepareBeanFactory(beanFactory);

            try {
                this.postProcessBeanFactory(beanFactory);
                StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
                this.invokeBeanFactoryPostProcessors(beanFactory);
                this.registerBeanPostProcessors(beanFactory);
                beanPostProcess.end();
                this.initMessageSource();
                this.initApplicationEventMulticaster();
                this.onRefresh();
                this.registerListeners();
                this.finishBeanFactoryInitialization(beanFactory);
                this.finishRefresh();
            } catch (BeansException var10) {
                if (this.logger.isWarnEnabled()) {
                    this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var10);
                }

                this.destroyBeans();
                this.cancelRefresh(var10);
                throw var10;
            } finally {
                this.resetCommonCaches();
                contextRefresh.end();
            }

        }
    }

之后会慢慢开始学习这里！，新建公众号：随风的java开发人生，欢迎互关互助。