厉害了！SpringBoot是如何动起来的！

程序入口

springapplication.run(beautyapplication.class, args);

 

执行此方法来加载整个springboot的环境。

1. 从哪儿开始？

springapplication.java

  /**
     * 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) {
        //...
  }

 

调用springapplication.java 中的 run 方法，目的是加载spring application，同时返回 applicationcontext。

2. 执行了什么？

2.1 计时

记录整个spring application的加载时间！

stopwatch stopwatch = new stopwatch();
stopwatch.start();
// ...
stopwatch.stop();
if (this.logstartupinfo) {
    new startupinfologger(this.mainapplicationclass)
            .logstarted(getapplicationlog(), stopwatch);
}

 

2.2 声明

// 声明 applicationcontext
configurableapplicationcontext context = null;
// 声明 一个异常报告集合
collection<springbootexceptionreporter> exceptionreporters = new arraylist<>();

 

2.3 指定程序运行模式

指定 java.awt.headless，默认是true 一般是在程序开始激活headless模式，告诉程序，现在你要工作在headless mode下，就不要指望硬件帮忙了，你得自力更生，依靠系统的计算能力模拟出这些特性来。

private void configureheadlessproperty() {
    system.setproperty(system_property_java_awt_headless, system.getproperty(
            system_property_java_awt_headless, boolean.tostring(this.headless)));
}

 

2.4 配置监听并发布应用启动事件

springapplicationrunlistener 负责加载 applicationlistener事件。

springapplicationrunlisteners listeners = getrunlisteners(args);
// 开始
listeners.starting();
// 处理所有 property sources 配置和 profiles 配置，准备环境，分为标准 servlet 环境和标准环境
configurableenvironment environment = prepareenvironment(listeners,applicationarguments);
// 准备应用上下文
preparecontext(context, environment, listeners, applicationarguments,printedbanner);
// 完成
listeners.started(context);
// 异常
handlerunfailure(context, ex, exceptionreporters, listeners);
// 执行
listeners.running(context);

 

getrunlisteners 中根据 type = springapplicationrunlistener.class 去拿到了所有的 listener 并根据优先级排序。

对应的就是 meta-inf/spring.factories 文件中的 org.springframework.boot.springapplicationrunlistener=org.springframework.boot.context.event.eventpublishingrunlistener

private <t> collection<t> getspringfactoriesinstances(class<t> type,
            class<?>[] parametertypes, object... args) {
        classloader classloader = thread.currentthread().getcontextclassloader();
        // use names and ensure unique to protect against duplicates
        set<string> names = new linkedhashset<>(
                springfactoriesloader.loadfactorynames(type, classloader));
        list<t> instances = createspringfactoriesinstances(type, parametertypes,
                classloader, args, names);
        annotationawareordercomparator.sort(instances);
        return instances;
    }

 

在 applicationlistener 中 , 可以针对任何一个阶段插入处理代码。

public interface springapplicationrunlistener {

    /**
     * called immediately when the run method has first started. can be used for very
     * early initialization.
     */
    void starting();

    /**
     * called once the environment has been prepared, but before the
     * {@link applicationcontext} has been created.
     * @param environment the environment
     */
    void environmentprepared(configurableenvironment environment);

    /**
     * called once the {@link applicationcontext} has been created and prepared, but
     * before sources have been loaded.
     * @param context the application context
     */
    void contextprepared(configurableapplicationcontext context);

    /**
     * called once the application context has been loaded but before it has been
     * refreshed.
     * @param context the application context
     */
    void contextloaded(configurableapplicationcontext context);

    /**
     * the context has been refreshed and the application has started but
     * {@link commandlinerunner commandlinerunners} and {@link applicationrunner
     * applicationrunners} have not been called.
     * @param context the application context.
     * @since 2.0.0
     */
    void started(configurableapplicationcontext context);

    /**
     * called immediately before the run method finishes, when the application context has
     * been refreshed and all {@link commandlinerunner commandlinerunners} and
     * {@link applicationrunner applicationrunners} have been called.
     * @param context the application context.
     * @since 2.0.0
     */
    void running(configurableapplicationcontext context);

    /**
     * called when a failure occurs when running the application.
     * @param context the application context or {@code null} if a failure occurred before
     * the context was created
     * @param exception the failure
     * @since 2.0.0
     */
    void failed(configurableapplicationcontext context, throwable exception);

}

 

3. 每个阶段执行的内容

3.1 listeners.starting();

在加载spring application之前执行，所有资源和环境未被加载。

3.2 prepareenvironment(listeners, applicationarguments);

创建 configurableenvironment；将配置的环境绑定到spring application中；

    private configurableenvironment prepareenvironment(
            springapplicationrunlisteners listeners,
            applicationarguments applicationarguments) {
        // create and configure the environment
        configurableenvironment environment = getorcreateenvironment();
        configureenvironment(environment, applicationarguments.getsourceargs());
        listeners.environmentprepared(environment);
        bindtospringapplication(environment);
        if (this.webapplicationtype == webapplicationtype.none) {
            environment = new environmentconverter(getclassloader())
                    .converttostandardenvironmentifnecessary(environment);
        }
        configurationpropertysources.attach(environment);
        return environment;
    }

 

3.3 preparecontext

配置忽略的bean；

 private void configureignorebeaninfo(configurableenvironment environment) {
        if (system.getproperty(
                cachedintrospectionresults.ignore_beaninfo_property_name) == null) {
            boolean ignore = environment.getproperty("spring.beaninfo.ignore",
                    boolean.class, boolean.true);
            system.setproperty(cachedintrospectionresults.ignore_beaninfo_property_name,
                    ignore.tostring());
        }
    }

 

打印日志-加载的资源

banner printedbanner = printbanner(environment);

 

根据不同的webapplicationtype创建context

context = createapplicationcontext();

 

3.4 refreshcontext

支持定制刷新

 /**
     * register a shutdown hook with the jvm runtime, closing this context
     * on jvm shutdown unless it has already been closed at that time.
     * <p>this method can be called multiple times. only one shutdown hook
     * (at max) will be registered for each context instance.
     * @see java.lang.runtime#addshutdownhook
     * @see #close()
     */
    void registershutdownhook();

 

3.5 afterrefresh

刷新后的实现方法暂未实现

 /**
     * called after the context has been refreshed.
     * @param context the application context
     * @param args the application arguments
     */
    protected void afterrefresh(configurableapplicationcontext context,
            applicationarguments args) {
    }

 

3.6 listeners.started(context);

到此为止， spring application的环境和资源都加载完毕了；发布应用上下文启动完成事件；执行所有 runner 运行器 - 执行所有 applicationrunner 和 commandlinerunner 这两种运行器。

// 启动
callrunners(context, applicationarguments);

 

3.7 listeners.running(context);

触发所有 springapplicationrunlistener 监听器的 running 事件方法

 

（完）

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