Springboot詳解底層啟動過程

更新時間：2022年07月11日 11:47:44 作者：PnJg?

這篇文章主要介紹了SpringBoot啟動過程的實現(xiàn)，文中通過示例代碼介紹的非常詳細，對大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

SpringApplication構(gòu)造分析

1、記錄 BeanDefinition 源

spring容器剛開始是空的，要去各個源找到beanDefinition，這些源可能是配置類，可能是xml文件。在構(gòu)造方法里會獲取一個主源，也就是引導(dǎo)類，根據(jù)引導(dǎo)類去獲取beanDefinition。

2、推斷應(yīng)用類型

根據(jù)jar包去判斷是什么引用類型

3、記錄 ApplicationContext 初始化器

對ApplicationContext做擴展

4、記錄監(jiān)聽器

監(jiān)聽重要事件

5、推斷主啟動類

記錄運行的主類。

SpringApplication run分析

1、得到 SpringApplicationRunListeners，名字取得不好，實際是事件發(fā)布器

發(fā)布 application starting 事件，在程序啟動的重要節(jié)點發(fā)布事件

    public static void main(String[] args) throws Exception{
        // 添加 app 監(jiān)聽器
        SpringApplication app = new SpringApplication();
        app.addListeners(e -> System.out.println(e.getClass()));
        // 獲取事件發(fā)送器實現(xiàn)類名
        List<String> names = SpringFactoriesLoader.loadFactoryNames(SpringApplicationRunListener.class, A39_2.class.getClassLoader());
        for (String name : names) {
            System.out.println(name);
            Class<?> clazz = Class.forName(name);
            Constructor<?> constructor = clazz.getConstructor(SpringApplication.class, String[].class);
            SpringApplicationRunListener publisher = (SpringApplicationRunListener) constructor.newInstance(app, args);
            // 發(fā)布事件
            DefaultBootstrapContext bootstrapContext = new DefaultBootstrapContext();
            publisher.starting(bootstrapContext); // spring boot 開始啟動
            publisher.environmentPrepared(bootstrapContext, new StandardEnvironment()); // 環(huán)境信息準備完畢
            GenericApplicationContext context = new GenericApplicationContext();
            publisher.contextPrepared(context); // 在 spring 容器創(chuàng)建，并調(diào)用初始化器之后，發(fā)送此事件
            publisher.contextLoaded(context); // 所有 bean definition 加載完畢
            context.refresh();
            publisher.started(context); // spring 容器初始化完成(refresh 方法調(diào)用完畢)
            publisher.running(context); // spring boot 啟動完畢
            publisher.failed(context, new Exception("出錯了")); // spring boot 啟動出錯
        }

2、封裝啟動 args

3、準備 Environment 添加命令行參數(shù)（*）

public static void main(String[] args) throws IOException {
        ApplicationEnvironment env = new ApplicationEnvironment(); // 系統(tǒng)環(huán)境變量, properties, yaml
        env.getPropertySources().addLast(new ResourcePropertySource(new ClassPathResource("step3.properties")));
        env.getPropertySources().addFirst(new SimpleCommandLinePropertySource(args));
        for (PropertySource<?> ps : env.getPropertySources()) {
            System.out.println(ps);
        }
//        System.out.println(env.getProperty("JAVA_HOME"));
        System.out.println(env.getProperty("server.port"));
    }

4、ConfigurationPropertySources 處理（*）

發(fā)布 application environment 已準備事件

    public static void main(String[] args) throws IOException, NoSuchFieldException {
        ApplicationEnvironment env = new ApplicationEnvironment();
        env.getPropertySources().addLast(
                new ResourcePropertySource("step4", new ClassPathResource("step4.properties"))
        );
        ConfigurationPropertySources.attach(env);
        for (PropertySource<?> ps : env.getPropertySources()) {
            System.out.println(ps);
        }
        System.out.println(env.getProperty("user.first-name"));
        System.out.println(env.getProperty("user.middle-name"));
        System.out.println(env.getProperty("user.last-name"));
    }
}

5、通過 EnvironmentPostProcessorApplicationListener 進行 env 后處理（*）

application.properties，由 StandardConfigDataLocationResolver 解析

spring.application.json

public class Step5 {
    public static void main(String[] args) {
        SpringApplication app = new SpringApplication();
        app.addListeners(new EnvironmentPostProcessorApplicationListener());
        /*List<String> names = SpringFactoriesLoader.loadFactoryNames(EnvironmentPostProcessor.class, Step5.class.getClassLoader());
        for (String name : names) {
            System.out.println(name);
        }*/
        EventPublishingRunListener publisher = new EventPublishingRunListener(app, args);
        ApplicationEnvironment env = new ApplicationEnvironment();
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>> 增強前");
        for (PropertySource<?> ps : env.getPropertySources()) {
            System.out.println(ps);
        }
        publisher.environmentPrepared(new DefaultBootstrapContext(), env);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>> 增強后");
        for (PropertySource<?> ps : env.getPropertySources()) {
            System.out.println(ps);
        }
    }
    private static void test1() {
        SpringApplication app = new SpringApplication();
        ApplicationEnvironment env = new ApplicationEnvironment();
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>> 增強前");
        for (PropertySource<?> ps : env.getPropertySources()) {
            System.out.println(ps);
        }
        ConfigDataEnvironmentPostProcessor postProcessor1 = new ConfigDataEnvironmentPostProcessor(new DeferredLogs(), new DefaultBootstrapContext());
        postProcessor1.postProcessEnvironment(env, app);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>> 增強后");
        for (PropertySource<?> ps : env.getPropertySources()) {
            System.out.println(ps);
        }
        RandomValuePropertySourceEnvironmentPostProcessor postProcessor2 = new RandomValuePropertySourceEnvironmentPostProcessor(new DeferredLog());
        postProcessor2.postProcessEnvironment(env, app);
        System.out.println(">>>>>>>>>>>>>>>>>>>>>>>>> 增強后");
        for (PropertySource<?> ps : env.getPropertySources()) {
            System.out.println(ps);
        }
        System.out.println(env.getProperty("server.port"));
        System.out.println(env.getProperty("random.int"));
        System.out.println(env.getProperty("random.int"));
        System.out.println(env.getProperty("random.int"));
        System.out.println(env.getProperty("random.uuid"));
        System.out.println(env.getProperty("random.uuid"));
        System.out.println(env.getProperty("random.uuid"));
    }
}

6、綁定 spring.main 到 SpringApplication 對象（*）

把配置文件中的值賦給SpringApplication的默認屬性值

public class Step6 {
    // 綁定 spring.main 前綴的 key value 至 SpringApplication, 請通過 debug 查看
    public static void main(String[] args) throws IOException {
        SpringApplication application = new SpringApplication();
        ApplicationEnvironment env = new ApplicationEnvironment();
        env.getPropertySources().addLast(new ResourcePropertySource("step6", new ClassPathResource("step6.properties")));
        System.out.println(application);
        Binder.get(env).bind("spring.main", Bindable.ofInstance(application));
        System.out.println(application);
    }

7、打印 banner（*）

public class Step7 {
    public static void main(String[] args) {
        ApplicationEnvironment env = new ApplicationEnvironment();
        SpringApplicationBannerPrinter printer = new SpringApplicationBannerPrinter(
                new DefaultResourceLoader(),
                new SpringBootBanner()
        );
        // 測試文字 banner
//        env.getPropertySources().addLast(new MapPropertySource("custom", Map.of("spring.banner.location","banner1.txt")));
        // 測試圖片 banner
//        env.getPropertySources().addLast(new MapPropertySource("custom", Map.of("spring.banner.image.location","banner2.png")));
        // 版本號的獲取
        System.out.println(SpringBootVersion.getVersion());
        printer.print(env, Step7.class, System.out);
    }
}

8、創(chuàng)建容器

    private static GenericApplicationContext createApplicationContext(WebApplicationType type) {
        GenericApplicationContext context = null;
        switch (type) {
            case SERVLET -> context = new AnnotationConfigServletWebServerApplicationContext();
            case REACTIVE -> context = new AnnotationConfigReactiveWebServerApplicationContext();
            case NONE -> context = new AnnotationConfigApplicationContext();
        }
        return context;
    }

9、準備容器發(fā)布

application context 已初始化事件

10、加載 bean 定義

發(fā)布 application prepared 事件

        DefaultListableBeanFactory beanFactory = context.getDefaultListableBeanFactory();
        AnnotatedBeanDefinitionReader reader1 = new AnnotatedBeanDefinitionReader(beanFactory);
        XmlBeanDefinitionReader reader2 = new XmlBeanDefinitionReader(beanFactory);
        ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(beanFactory);
        reader1.register(Config.class);
        reader2.loadBeanDefinitions(new ClassPathResource("b03.xml"));
        scanner.scan("com.itheima.a39.sub");

11、refresh 容器

發(fā)布 application started 事件

12、執(zhí)行 runner