他會調(diào)用 ((AbstractApplicationContext) applicationContext).refresh();方法，我們點進來看

public void refresh() throws BeansException, IllegalStateException {
   synchronized (this.startupShutdownMonitor) {
      // Prepare this context for refreshing.
      prepareRefresh();

      // Tell the subclass to refresh the internal bean factory.
      ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

      // Prepare the bean factory for use in this context.
      prepareBeanFactory(beanFactory);

      try {
         // Allows post-processing of the bean factory in context subclasses.
         postProcessBeanFactory(beanFactory);

         // Invoke factory processors registered as beans in the context.
         invokeBeanFactoryPostProcessors(beanFactory);

         // Register bean processors that intercept bean creation.
         registerBeanPostProcessors(beanFactory);

         // Initialize message source for this context.
         initMessageSource();

         // Initialize event multicaster for this context.
         initApplicationEventMulticaster();

         // Initialize other special beans in specific context subclasses.
         onRefresh();

         // Check for listener beans and register them.
         registerListeners();

         // Instantiate all remaining (non-lazy-init) singletons.
         finishBeanFactoryInitialization(beanFactory);

         // Last step: publish corresponding event.
         finishRefresh();
      }

      catch (BeansException ex) {
         if (logger.isWarnEnabled()) {
            logger.warn("Exception encountered during context initialization - " +
                  "cancelling refresh attempt: " + ex);
         }

         // Destroy already created singletons to avoid dangling resources.
         destroyBeans();

         // Reset 'active' flag.
         cancelRefresh(ex);

         // Propagate exception to caller.
         throw ex;
      }

      finally {
         // Reset common introspection caches in Spring's core, since we
         // might not ever need metadata for singleton beans anymore...
         resetCommonCaches();
      }
   }
}

這點代碼似曾相識啊 沒錯，就是一個spring的bean的加載過程我在，解析springIOC加載過程的時候介紹過這里面的方法，如果你看過Spring源碼的話 ，應該知道這些方法都是做什么的。現(xiàn)在我們不關(guān)心其他的，我們來看一個方法叫做 onRefresh();方法

protected void onRefresh() throws BeansException {
   // For subclasses: do nothing by default.
}

他在這里并沒有實現(xiàn)，但是我們找他的其他實現(xiàn)，我們來找

我們既然要找Tomcat那就肯定跟web有關(guān)，我們可以看到有個ServletWebServerApplicationContext

@Override
protected void onRefresh() {
   super.onRefresh();
   try {
      createWebServer();
   }
   catch (Throwable ex) {
      throw new ApplicationContextException("Unable to start web server", ex);
   }
}

我們可以看到有一個createWebServer();方法他是創(chuàng)建web容器的，而Tomcat不就是web容器，那他是怎么創(chuàng)建的呢，我們繼續(xù)看

private void createWebServer() {
   WebServer webServer = this.webServer;
   ServletContext servletContext = getServletContext();
   if (webServer == null && servletContext == null) {
      ServletWebServerFactory factory = getWebServerFactory();
      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();
}

factory.getWebServer(getSelfInitializer());他是通過工廠的方式創(chuàng)建的

public interface ServletWebServerFactory {

   WebServer getWebServer(ServletContextInitializer... initializers);

}

可以看到 它是一個接口，為什么會是接口。因為我們不止是Tomcat一種web容器。

我們看到還有Jetty，那我們來看TomcatServletWebServerFactory

@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
   Tomcat tomcat = new Tomcat();
   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);
   configureEngine(tomcat.getEngine());
   for (Connector additionalConnector : this.additionalTomcatConnectors) {
      tomcat.getService().addConnector(additionalConnector);
   }
   prepareContext(tomcat.getHost(), initializers);
   return getTomcatWebServer(tomcat);
}

那這塊代碼，就是我們要尋找的內(nèi)置Tomcat，在這個過程當中，我們可以看到創(chuàng)建Tomcat的一個流程。因為run方法里面加載的東西很多，所以今天就淺談到這里。如果不明白的話， 我們在用另一種方式來理解下，

大家要應該都知道stater舉點例子

<dependency>
    <groupId>org.springframework.boot<span class="hljs-name"groupId>
    <artifactId>spring-boot-starter-data-redis<span class="hljs-name"artifactId>
<span class="hljs-name"dependency>
<dependency>
    <groupId>org.springframework.boot<span class="hljs-name"groupId>
    <artifactId>spring-boot-starter-freemarker<span class="hljs-name"artifactId>
<span class="hljs-name"dependency>

所以我們不防不定義一個stater來理解下，我們做一個需求，就是定制化不同的人跟大家說你們好，我們來看

<parent>
    <groupId>org.springframework.boot<span class="hljs-name"groupId>
    <artifactId>spring-boot-starter-parent<span class="hljs-name"artifactId>
    <version>2.1.4.RELEASE<span class="hljs-name"version>
    <relativePath/>
<span class="hljs-name"parent>
<groupId>com.zgw<span class="hljs-name"groupId>
<artifactId>gw-spring-boot-srater<span class="hljs-name"artifactId>
<version>1.0-SNAPSHOT<span class="hljs-name"version>

<dependencies>
    <dependency>
        <groupId>org.springframework.boot<span class="hljs-name"groupId>
        <artifactId>spring-boot-autoconfigure<span class="hljs-name"artifactId>
    <span class="hljs-name"dependency>
<span class="hljs-name"dependencies>

我們先來看maven配置寫入版本號，如果自定義一個stater的話必須依賴spring-boot-autoconfigure這個包,我們先看下項目目錄

public class GwServiceImpl  implements GwService{
    @Autowired
    GwProperties properties;

    @Override
    public void Hello()
    {
        String name=properties.getName();
        System.out.println(name+"說:你們好啊");
    }
}

我們做的就是通過配置文件來定制name這個是具體實現(xiàn)

@Component
@ConfigurationProperties(prefix = "spring.gwname")
public class GwProperties {

    String name="zgw";

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

這個類可以通過@ConfigurationProperties讀取配置文件

@Configuration
@ConditionalOnClass(GwService.class)  //掃描類
@EnableConfigurationProperties(GwProperties.class) //讓配置類生效
public class GwAutoConfiguration {

    /**
    * 功能描述 托管給spring
    * @author zgw
    * @return
    */
    @Bean
    @ConditionalOnMissingBean
    public GwService gwService()
    {
        return new GwServiceImpl();
    }
}

這個為配置類，為什么這么寫因為，spring-boot的stater都是這么寫的，我們可以參照他仿寫stater，以達到自動配置的目的，然后我們在通過spring.factories也來進行配置

org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.gw.GwAutoConfiguration

然后這樣一個簡單的stater就完成了，然后可以進行maven的打包，在其他項目引入就可以使用，在這里列出代碼地址