从入口看springboot

前言

看很多springboot相关书籍，都是先讲框架，讲设计模式，讲模块，讲扩展功能，但是往往只能给读者形成一个大概的印象或者作为一本工具来用，或者作为一本面试准备书籍。所谓一知半解大概就是现在我的状态，能熟练使用，也能说出一些原理，但是没有串联起来，没法全局看问题，站在巨人的肩膀只能看到巨人的脚。

回想我工作中处理各种问题，也是从入口处，一步一步往下走，因此也准备从springboot启动main方法一步一步往下走，看springboot具体经历了什么 ，载入提炼整个springboot的框架结构。

最简单的springboot启动类

/**
 * springboot原理学习项目
 */
@SpringBootApplication
public class SpringLeanApplication {
    public static void main(String[] args) {
        /// springboot是提供启动入口
        SpringApplication.run(SpringLeanApplication.class, args);
    }
}

类SpringApplication备注

 * <ul>
 * <li>Create an appropriate {@link ApplicationContext} instance (depending on your
 * classpath)</li>
 * <li>Register a {@link CommandLinePropertySource} to expose command line arguments as
 * Spring properties</li>
 * <li>Refresh the application context, loading all singleton beans</li>
 * <li>Trigger any {@link CommandLineRunner} beans</li>
 * </ul>

1.  创建ApplicationContext实例
3.  刷新上下文，加载所有的单例bean对象
2.4暂时忽略 

写备注很重要，写来是看的，别只看代码，也要看备注啊

顺便说一句，作者很多，合作很重要

 * @author Phillip Webb
 * @author Dave Syer
 * @author Andy Wilkinson
 * @author Christian Dupuis
 * @author Stephane Nicoll
 * @author Jeremy Rickard
 * @author Craig Burke
 * @author Michael Simons
 * @author Madhura Bhave
 * @author Brian Clozel
 * @author Ethan Rubinson
 * @since 1.0.0

第一章 启动调用关系

// 方法1
 public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
    return run(new Class<?>[] { primarySource }, args);
}
// 方法2
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
    return new SpringApplication(primarySources).run(args); // run执行启动
}
// 方法3
public SpringApplication(Class<?>... primarySources) {
    this(null, primarySources);
}
// 方法4
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
    this.resourceLoader = resourceLoader;
    Assert.notNull(primarySources, "PrimarySources must not be null");
    this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        // 1)web启动类型 react/servlet/非web启动
    this.webApplicationType = WebApplicationType.deduceFromClasspath();
       // 2)设置初始化类
    setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
       // 3)设置监听
    setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
    this.mainApplicationClass = deduceMainApplicationClass();
}

SpringApplication做了3件事情

1. 设置web启动类型
2. 加载initializer

0 = "org.springframework.boot.devtools.restart.RestartScopeInitializer"
1 = "org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer"
2 = "org.springframework.boot.context.ContextIdApplicationContextInitializer"
3 = "org.springframework.boot.context.config.DelegatingApplicationContextInitializer"
4 = "org.springframework.boot.rsocket.context.RSocketPortInfoApplicationContextInitializer"
5 = "org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer"
6 = "org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer"
7 = "org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener"

3. 加载listener

0 = "org.springframework.boot.devtools.restart.RestartApplicationListener"
1 = "org.springframework.boot.devtools.logger.DevToolsLogFactory.Listener"
2 = "org.springframework.boot.ClearCachesApplicationListener"
3 = "org.springframework.boot.builder.ParentContextCloserApplicationListener"
4 = "org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor"
5 = "org.springframework.boot.context.FileEncodingApplicationListener"
6 = "org.springframework.boot.context.config.AnsiOutputApplicationListener"
7 = "org.springframework.boot.context.config.ConfigFileApplicationListener"
8 = "org.springframework.boot.context.config.DelegatingApplicationListener"
9 = "org.springframework.boot.context.logging.ClasspathLoggingApplicationListener"
10 = "org.springframework.boot.context.logging.LoggingApplicationListener"
11 = "org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener"
12 = "org.springframework.boot.autoconfigure.BackgroundPreinitializer"

第二章 SpringApplication.run()方法说明

run方法执行最终的启动过程

/**
    * Run the Spring application, creating and refreshing a new
     * {@link ApplicationContext}.
     * @param args the application arguments (usually passed from a Java main method)
     * @return a running {@link ApplicationContext}
     */
    public ConfigurableApplicationContext run(String... args) {
                // 秒表 统计多个任务执行时长
        StopWatch stopWatch = new StopWatch();
        stopWatch.start();
        ConfigurableApplicationContext context = null;
        Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
               // 后面有说明，很久以前生成验证码的时候遇到的一个问题记录了下
        configureHeadlessProperty();
               // 获取runlistener
        SpringApplicationRunListeners listeners = getRunListeners(args);
               // 推送ApplicationStartingEvent事件
        listeners.starting();
        try {
                        // 获取启动参数
            ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
                        // 方法2
            ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
            // 方法3
                        configureIgnoreBeanInfo(environment);
                       // 打印banner
            Banner printedBanner = printBanner(environment);
            context = createApplicationContext();
            exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
            prepareContext(context, environment, listeners, applicationArguments, printedBanner);
            refreshContext(context);
            afterRefresh(context, applicationArguments);
            stopWatch.stop();
            if (this.logStartupInfo) {
                new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
            }
            listeners.started(context);
            callRunners(context, applicationArguments);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, listeners);
            throw new IllegalStateException(ex);
        }

        try {
            listeners.running(context);
        }
        catch (Throwable ex) {
            handleRunFailure(context, ex, exceptionReporters, null);
            throw new IllegalStateException(ex);
        }
        return context;
    }

1. headless说明

截屏2020-04-08 下午9.00.23.png

2. getRunListeners说明

创建SpringApplicationRunListeners，包含以下listener

org.springframework.boot.context.event.EventPublishingRunListener

SpringApplicationRunListener内部包含ApplicationEventMulticaster，用于管理对多个ApplicationListener（参考SpringApplication初始化）推送SpringApplicationEvent事件

3. SpringApplicationRunListener

持续更新中。。。