Spring的加載程序-組態檔加載程序（一）

1、原因

不知不覺已經從事java開發好幾年了，成了人們口中的老司機，但是一直都是恍恍惚惚過來，對于框架底層實作一直都沒有怎么了解過，只是在面試的時候背些面試題，慢慢地發現不能這樣，需要振作，笑~~~~，從這篇開始，記錄自己對于Spring加載程序的原始碼查看，

2、開始

1、在Spring加載bean并獲取bean定義的常用類是ClassPathXmlApplicationContext 以及AnnotationConfigApplicationContext，ClassPathXmlApplicationContext用來讀取并加載默認classpath 路徑下面的組態檔，AnnotationConfigApplicationContext是加載注解@Configuration標注的配置類，我現在關注于ClassPathXmlApplicationContext，

2、新建一個maven專案，并引入spring相關jar包，

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

spring-boot-starter-we會依賴引入spring-context包，定義介面以及實作類

public interface Person {

    void say();
}

@Log4j2
public class Teacher implements Person {

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

撰寫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" />
</beans>

開始撰寫測驗類用來測驗bean加載程序：

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

    }

第一行打上斷點，debug開始跟著走，就會來到：

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

    }        

點擊this.refresh()方法進入就來到了最核心的地方，這里弄懂了，bean加載就弄懂了：

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();
            }

        }
    }

之后會慢慢開始學習這里！，新建公眾號：隨風的java開發人生，歡迎互關互助，

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