SpringBoot通过main方法启动web项目实践

@springbootapplication
public class demoapplication {
    public static void main(string[] args) {
        springapplication.run(demoapplication.class, args);
    }
}

// springapplication 构造函数核心逻辑
public springapplication(resourceloader resourceloader, class<?>... primarysources) {
    // 1. 设置资源加载器
    this.resourceloader = resourceloader;
    // 2. 校验并保存主配置类（即 @springbootapplication 标注的类）
    this.primarysources = new linkedhashset<>(arrays.aslist(primarysources));
    // 3. 推断应用类型（reactive、servlet、none）
    this.webapplicationtype = webapplicationtype.deducefromclasspath();
    // 4. 加载并实例化 applicationcontextinitializer
    setinitializers((collection) getspringfactoriesinstances(applicationcontextinitializer.class));
    // 5. 加载并实例化 applicationlistener
    setlisteners((collection) getspringfactoriesinstances(applicationlistener.class));
    // 6. 推断 main 方法所在类
    this.mainapplicationclass = deducemainapplicationclass();
}

public configurableapplicationcontext run(string... args) {
    // 1. 计时和发布启动事件
    stopwatch stopwatch = new stopwatch();
    stopwatch.start();
    configurableapplicationcontext context = null;
    collection<springbootexceptionreporter> exceptionreporters = new arraylist<>();
    configureheadlessproperty();
    
    // 2. 获取并启动监听器
    springapplicationrunlisteners listeners = getrunlisteners(args);
    listeners.starting();
    
    try {
        // 3. 构建应用参数和环境配置
        applicationarguments applicationarguments = new defaultapplicationarguments(args);
        configurableenvironment environment = prepareenvironment(listeners, applicationarguments);
        
        // 4. 创建并配置 applicationcontext
        context = createapplicationcontext();
        exceptionreporters = getspringfactoriesinstances(springbootexceptionreporter.class,
                new class[] { configurableapplicationcontext.class }, context);
        
        // 5. 准备上下文（加载 bean 定义）
        preparecontext(context, environment, listeners, applicationarguments, printedbanner);
        // 6. 刷新上下文（核心启动逻辑）
        refreshcontext(context);
        // 7. 刷新后的回调处理
        afterrefresh(context, applicationarguments);
        // 8. 发布应用就绪事件
        listeners.started(context);
        // 9. 执行 runner（如 commandlinerunner）
        callrunners(context, applicationarguments);
    }
    catch (throwable ex) {
        handlerunfailure(context, ex, exceptionreporters, listeners);
        throw new illegalstateexception(ex);
    }
    
    stopwatch.stop();
    if (this.logstartupinfo) {
        new startupinfologger(this.mainapplicationclass).logstarted(getapplicationlog(), stopwatch);
    }
    // 10. 发布应用运行中事件
    listeners.running(context);
    return context;
}

private void refreshcontext(configurableapplicationcontext context) {
    refresh(context);
    if (this.registershutdownhook) {
        try {
            context.registershutdownhook();
        }
        catch (accesscontrolexception ex) {
            // not allowed in some environments.
        }
    }
}

protected void refresh(configurableapplicationcontext context) {
    // 调用 abstractapplicationcontext 的 refresh() 方法
    context.refresh();
}

// servletwebserverapplicationcontext 核心方法
@override
protected void onrefresh() {
    super.onrefresh();
    try {
        // 创建并启动嵌入式 web 服务器
        createwebserver();
    }
    catch (throwable ex) {
        throw new applicationcontextexception("unable to start web server", ex);
    }
}

private void createwebserver() {
    webserver webserver = this.webserver;
    servletcontext servletcontext = getservletcontext();
    
    if (webserver == null && servletcontext == null) {
        // 1. 获取 servletwebserverfactory（如 tomcatservletwebserverfactory）
        servletwebserverfactory factory = getwebserverfactory();
        // 2. 创建并配置 web 服务器
        this.webserver = factory.getwebserver(getselfinitializer());
    }
    else if (servletcontext != null) {
        try {
            getselfinitializer().onstartup(servletcontext);
        }
        catch (servletexception ex) {
            throw new applicationcontextexception("cannot initialize servlet context", ex);
        }
    }
    initpropertysources();
}

@override
public webserver getwebserver(servletcontextinitializer... initializers) {
    // 1. 创建 tomcat 实例
    tomcat tomcat = new tomcat();
    // 2. 配置服务器基本参数（端口、上下文路径等）
    file basedir = (this.basedirectory != null) ? this.basedirectory : createtempdir("tomcat");
    tomcat.setbasedir(basedir.getabsolutepath());
    connector connector = new connector(this.protocol);
    tomcat.getservice().addconnector(connector);
    customizeconnector(connector);
    tomcat.setconnector(connector);
    tomcat.gethost().setautodeploy(false);
    // 3. 配置 servletcontextinitializer（如 dispatcherservlet）
    preparecontext(tomcat.gethost(), initializers);
    // 4. 启动服务器
    return gettomcatwebserver(tomcat);
}

@bean
@primary
@conditionalonmissingbean(dispatcherservlet.class)
public dispatcherservlet dispatcherservlet(webmvcproperties properties) {
    dispatcherservlet dispatcherservlet = new dispatcherservlet();
    dispatcherservlet.setdispatchoptionsrequest(properties.isdispatchoptionsrequest());
    dispatcherservlet.setdispatchtracerequest(properties.isdispatchtracerequest());
    dispatcherservlet.setthrowexceptionifnohandlerfound(properties.isthrowexceptionifnohandlerfound());
    dispatcherservlet.setpublishevents(properties.ispublishrequesthandledevents());
    dispatcherservlet.setenableloggingrequestdetails(properties.islogrequestdetails());
    return dispatcherservlet;
}