nohup java -jar -Xms128m -Xmx128m -Xss256k -XX:+PrintGCDetails -XX:+PrintHeapAtGC -Xloggc:/data/log/web-gc.log web.jar >/data/log/web.log &

#配置程序端口，默認(rèn)為8080
server.port= 8080
#用戶會(huì)話session過期時(shí)間，以秒為單位
server.session.timeout=
#配置默認(rèn)訪問路徑，默認(rèn)為/
server.context-path=

# 配置Tomcat編碼,默認(rèn)為UTF-8
server.tomcat.uri-encoding=UTF-8
# 配置最大線程數(shù)
server.tomcat.max-threads=1000

public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
    return run(new Class[]{primarySource}, args);
}
// 這里run方法返回的是ConfigurableApplicationContext
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
 	return (new SpringApplication(primarySources)).run(args);
}

public ConfigurableApplicationContext run(String... args) {
 ConfigurableApplicationContext context = null;
 Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
 this.configureHeadlessProperty();
 SpringApplicationRunListeners listeners = this.getRunListeners(args);
 listeners.starting();
 Collection exceptionReporters;
 try {
  ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
  ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
  this.configureIgnoreBeanInfo(environment);
  //打印banner，這里可以自己涂鴉一下，換成自己項(xiàng)目的logo
  Banner printedBanner = this.printBanner(environment);
  //創(chuàng)建應(yīng)用上下文
  context = this.createApplicationContext();
  exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
  //預(yù)處理上下文
  this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
  //刷新上下文
  this.refreshContext(context);
  //再刷新上下文
  this.afterRefresh(context, applicationArguments);
  listeners.started(context);
  this.callRunners(context, applicationArguments);
 } catch (Throwable var10) {
 }
 try {
  listeners.running(context);
  return context;
 } catch (Throwable var9) {
 }
}

//創(chuàng)建上下文
protected ConfigurableApplicationContext createApplicationContext() {
 Class<?> contextClass = this.applicationContextClass;
 if (contextClass == null) {
  try {
   switch(this.webApplicationType) {
    case SERVLET:
                    //創(chuàng)建AnnotationConfigServletWebServerApplicationContext
        contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
     break;
    case REACTIVE:
     contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
     break;
    default:
     contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
   }
  } catch (ClassNotFoundException var3) {
   throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
  }
 }
 return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
}

//SpringApplication.java
//刷新上下文
private void refreshContext(ConfigurableApplicationContext context) {
 this.refresh(context);
 if (this.registerShutdownHook) {
  try {
   context.registerShutdownHook();
  } catch (AccessControlException var3) {
  }
 }
}
//這里直接調(diào)用最終父類AbstractApplicationContext.refresh()方法
protected void refresh(ApplicationContext applicationContext) {
 ((AbstractApplicationContext)applicationContext).refresh();
}

//AbstractApplicationContext.java
public void refresh() throws BeansException, IllegalStateException {
 synchronized(this.startupShutdownMonitor) {
  this.prepareRefresh();
  ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
  this.prepareBeanFactory(beanFactory);
  try {
   this.postProcessBeanFactory(beanFactory);
   this.invokeBeanFactoryPostProcessors(beanFactory);
   this.registerBeanPostProcessors(beanFactory);
   this.initMessageSource();
   this.initApplicationEventMulticaster();
   //調(diào)用各個(gè)子類的onRefresh()方法，也就說這里要回到子類：ServletWebServerApplicationContext，調(diào)用該類的onRefresh()方法
   this.onRefresh();
   this.registerListeners();
   this.finishBeanFactoryInitialization(beanFactory);
   this.finishRefresh();
  } catch (BeansException var9) {
   this.destroyBeans();
   this.cancelRefresh(var9);
   throw var9;
  } finally {
   this.resetCommonCaches();
  }
 }
}

//ServletWebServerApplicationContext.java
//在這個(gè)方法里看到了熟悉的面孔，this.createWebServer，神秘的面紗就要揭開了。
protected void onRefresh() {
 super.onRefresh();
 try {
  this.createWebServer();
 } catch (Throwable var2) {
 }
}
//ServletWebServerApplicationContext.java
//這里是創(chuàng)建webServer，但是還沒有啟動(dòng)tomcat，這里是通過ServletWebServerFactory創(chuàng)建，那么接著看下ServletWebServerFactory
private void createWebServer() {
 WebServer webServer = this.webServer;
 ServletContext servletContext = this.getServletContext();
 if (webServer == null && servletContext == null) {
  ServletWebServerFactory factory = this.getWebServerFactory();
  this.webServer = factory.getWebServer(new ServletContextInitializer[]{this.getSelfInitializer()});
 } else if (servletContext != null) {
  try {
   this.getSelfInitializer().onStartup(servletContext);
  } catch (ServletException var4) {
  }
 }
 this.initPropertySources();
}
//接口
public interface ServletWebServerFactory {
    WebServer getWebServer(ServletContextInitializer... initializers);
}
//實(shí)現(xiàn)
AbstractServletWebServerFactory
JettyServletWebServerFactory
TomcatServletWebServerFactory
UndertowServletWebServerFactory

//TomcatServletWebServerFactory.java
//這里我們使用的tomcat，所以我們查看TomcatServletWebServerFactory。到這里總算是看到了tomcat的蹤跡。
@Override
public WebServer getWebServer(ServletContextInitializer... initializers) {
 Tomcat tomcat = new Tomcat();
 File baseDir = (this.baseDirectory != null) ? this.baseDirectory : createTempDir("tomcat");
 tomcat.setBaseDir(baseDir.getAbsolutePath());
    //創(chuàng)建Connector對(duì)象
 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);
}
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
 return new TomcatWebServer(tomcat, getPort() >= 0);
}
//Tomcat.java
//返回Engine容器，看到這里，如果熟悉tomcat源碼的話，對(duì)engine不會(huì)感到陌生。
public Engine getEngine() {
    Service service = getServer().findServices()[0];
    if (service.getContainer() != null) {
        return service.getContainer();
    }
    Engine engine = new StandardEngine();
    engine.setName( "Tomcat" );
    engine.setDefaultHost(hostname);
    engine.setRealm(createDefaultRealm());
    service.setContainer(engine);
    return engine;
}
//Engine是最高級(jí)別容器，Host是Engine的子容器，Context是Host的子容器，Wrapper是Context的子容器

//TomcatWebServer.java
//這里調(diào)用構(gòu)造函數(shù)實(shí)例化TomcatWebServer
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
 Assert.notNull(tomcat, "Tomcat Server must not be null");
 this.tomcat = tomcat;
 this.autoStart = autoStart;
 initialize();
}
private void initialize() throws WebServerException {
    //在控制臺(tái)會(huì)看到這句日志
 logger.info("Tomcat initialized with port(s): " + getPortsDescription(false));
 synchronized (this.monitor) {
  try {
   addInstanceIdToEngineName();
   Context context = findContext();
   context.addLifecycleListener((event) -> {
    if (context.equals(event.getSource()) && Lifecycle.START_EVENT.equals(event.getType())) {
     removeServiceConnectors();
    }
   });
   //===啟動(dòng)tomcat服務(wù)===
   this.tomcat.start();
   rethrowDeferredStartupExceptions();
   try {
    ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
   }
   catch (NamingException ex) {
   }
            //開啟阻塞非守護(hù)進(jìn)程
   startDaemonAwaitThread();
  }
  catch (Exception ex) {
   stopSilently();
   destroySilently();
   throw new WebServerException("Unable to start embedded Tomcat", ex);
  }
 }
}

//Tomcat.java
public void start() throws LifecycleException {
 getServer();
 server.start();
}
//這里server.start又會(huì)回到TomcatWebServer的
public void stop() throws LifecycleException {
 getServer();
 server.stop();
}

//TomcatWebServer.java
//啟動(dòng)tomcat服務(wù)
@Override
public void start() throws WebServerException {
 synchronized (this.monitor) {
  if (this.started) {
   return;
  }
  try {
   addPreviouslyRemovedConnectors();
   Connector connector = this.tomcat.getConnector();
   if (connector != null && this.autoStart) {
    performDeferredLoadOnStartup();
   }
   checkThatConnectorsHaveStarted();
   this.started = true;
   //在控制臺(tái)打印這句日志，如果在yml設(shè)置了上下文，這里會(huì)打印
   logger.info("Tomcat started on port(s): " + getPortsDescription(true) + " with context path '"
     + getContextPath() + "'");
  }
  catch (ConnectorStartFailedException ex) {
   stopSilently();
   throw ex;
  }
  catch (Exception ex) {
   throw new WebServerException("Unable to start embedded Tomcat server", ex);
  }
  finally {
   Context context = findContext();
   ContextBindings.unbindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
  }
 }
}
//關(guān)閉tomcat服務(wù)
@Override
public void stop() throws WebServerException {
 synchronized (this.monitor) {
  boolean wasStarted = this.started;
  try {
   this.started = false;
   try {
    stopTomcat();
    this.tomcat.destroy();
   }
   catch (LifecycleException ex) {
   }
  }
  catch (Exception ex) {
   throw new WebServerException("Unable to stop embedded Tomcat", ex);
  }
  finally {
   if (wasStarted) {
    containerCounter.decrementAndGet();
   }
  }
 }
}

@SpringBootApplication
public class SpringBootHelloWorldTomcatApplication extends SpringBootServletInitializer {
	@Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        return builder.sources(Application.class);
    }
}

public class ServletInitializer extends SpringBootServletInitializer {
    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
        //此處的Application.class為帶有@SpringBootApplication注解的啟動(dòng)類
        return builder.sources(Application.class);
    }
}

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>

<dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.0.1</version>
</dependency>

<build>
    <finalName>test</finalName>
</build>

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {

@Override
public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
      throws ServletException {
   List<WebApplicationInitializer> initializers = new LinkedList<>();
   if (webAppInitializerClasses != null) {
      for (Class<?> waiClass : webAppInitializerClasses) {
        // 如果不是接口 不是抽象 跟WebApplicationInitializer有關(guān)系  就會(huì)實(shí)例化
         if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
               WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
            try {
               initializers.add((WebApplicationInitializer)
                     ReflectionUtils.accessibleConstructor(waiClass).newInstance());
            }
            catch (Throwable ex) {
               throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
            }
         }
      }
   }
   if (initializers.isEmpty()) {
      servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
      return;
   }
   servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
   // 排序
   AnnotationAwareOrderComparator.sort(initializers);
   for (WebApplicationInitializer initializer : initializers) {
      initializer.onStartup(servletContext);
   }
}

@Override
public void onStartup(ServletContext servletContext) throws ServletException {
   // Logger initialization is deferred in case an ordered
   // LogServletContextInitializer is being used
   this.logger = LogFactory.getLog(getClass());
   WebApplicationContext rootApplicationContext = createRootApplicationContext(servletContext);
   if (rootApplicationContext != null) {
      servletContext.addListener(new SpringBootContextLoaderListener(rootApplicationContext, servletContext));
   }
   else {
      this.logger.debug("No ContextLoaderListener registered, as createRootApplicationContext() did not "
            + "return an application context");
   }
}

protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) {
   SpringApplicationBuilder builder = createSpringApplicationBuilder();
   builder.main(getClass());
   ApplicationContext parent = getExistingRootWebApplicationContext(servletContext);
   if (parent != null) {
      this.logger.info("Root context already created (using as parent).");
      servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null);
      builder.initializers(new ParentContextApplicationContextInitializer(parent));
   }
   builder.initializers(new ServletContextApplicationContextInitializer(servletContext));
   builder.contextClass(AnnotationConfigServletWebServerApplicationContext.class);
   // 調(diào)用configure
   builder = configure(builder); //①
   builder.listeners(new WebEnvironmentPropertySourceInitializer(servletContext));
   SpringApplication application = builder.build();//②
   if (application.getAllSources().isEmpty()
         && MergedAnnotations.from(getClass(), SearchStrategy.TYPE_HIERARCHY).isPresent(Configuration.class)) {
      application.addPrimarySources(Collections.singleton(getClass()));
   }
   Assert.state(!application.getAllSources().isEmpty(),
         "No SpringApplication sources have been defined. Either override the "
               + "configure method or add an @Configuration annotation");
   // Ensure error pages are registered
   if (this.registerErrorPageFilter) {
      application.addPrimarySources(Collections.singleton(ErrorPageFilterConfiguration.class));
   }
   application.setRegisterShutdownHook(false);
   return run(application);//③
}

@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder builder) {
    return builder.sources(Application.class);
}

public SpringApplication build(String... args) {
   configureAsChildIfNecessary(args);
   this.application.addPrimarySources(this.sources);
   return this.application;
}

protected WebApplicationContext run(SpringApplication application) {
   return (WebApplicationContext) application.run();
}

public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
}