springboot 之 tomact 启动
“先脉络后细节”
我们知道自servlet3.0开始已经支持@WebServlet 用于将一个类声明为 Servlet，该注解将会在部署时被容器处理，容器将根据具体的属性配置将相应的类部署为 Servlet。也就是说我们可以不像以前那样将servlet、listener配置在web.xml中，使用注解的方式提供了非常方便的扩展性。比如我们即将和后续研究的 springboot 启动tomact并加载servlet(DispatcherServlet)
话不多说，直奔主题~
springboot 项目启动后会通过 SpringApplication.run() 方法启动服务，我们从入口进入springboot 的源码。通过run 方法一层一层跟入（
中间废柴代码略~
）在SpringApplication找到了如下代码
- 创建SpringApplication对象
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
//创建SpringApplication对象，并调用run()
return new SpringApplication(primarySources).run(args);
}
- 自动装载（先不深究自动装载哪些类）
我们看一下通过有参构造创建SpringApplication都做了哪事情：
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
//设置classloader
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
this.webApplicationType = WebApplicationType.deduceFromClasspath();
//从META-INF/spring.factories 中获取 ApplicationContextInitializer,而且这个中涉及到了一个重要的类 SpringFactoriesLoader（为了不打断主流程，这个类后续单独介绍）
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
//从META-INF/spring.facotories 中获取 ApplicationContextLinister
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
通过上边的代码我们知道，在创建SpringApplication过程中自动装载了spring.factories 的相关，我们继续完后走
-
调用run方法
在步骤1中创建对象后调用run方法
public ConfigurableApplicationContext run(String... args) {
//StopWatch 用于启动计时
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
//获取SpringApplicationRunListeners，从类路径下的META-INF/spring.factories
SpringApplicationRunListeners listeners = getRunListeners(args);
//回调所有的获取SpringApplicationRunListener.starting()方法
listeners.starting();
try {
//封装命令行参数
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
//加载外部化配置的资源到environment，并触发ApplicationEnvironmentPreparedEvent事件
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
configureIgnoreBeanInfo(environment);
// 打印banner图
Banner printedBanner = printBanner(environment);
//创建ApplicationContext，并通过webApplicationType 决定返回ConfigurableApplicationContext的具体类型
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//ConfigurableApplicationContext 配置或处理
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
//刷新ConfigurableApplicationContext
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
//所有的SpringApplicationRunListener回调finished方法
listeners.started(context);
//处理回调
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
- 启动重点获取ConfigurableApplicationContext
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
//web 项目返回 AnnotationConfigServletWebServerApplicationContext
case SERVLET:
contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass",
ex);
}
}
//并初始化
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
AnnotationConfigServletWebServerApplicationContext 通过这个东东的名字我们大概就能猜出和web容器的加载、启动有关，我们看这哥们究竟是干什么的
-
create web server & start
我们看代码发现WebApplicationContextServletContextAwareProcessor 继承自 ServletContextAwareProcessor，我们继续看 ServletContextAwareProcessor 里都有什么
看图中的方法你是不是已经看到些端倪了，我们通过上面的 第4步 已经知道，createApplicationContext 如果是web项目会返回AnnotationConfigServletWebServerApplicationContext，而AnnotationConfigServletWebServerApplicationContex继承自ServletWebServerApplicationContext，在 第3步 中返回AnnotationConfigServletWebServerApplicationContext 后执行了 refreshContext(context);
springboot 之 tomact 启动 我们继续看refersh，发现代码 springboot 之 tomact 启动
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
//ApplicationContxt refresh
((AbstractApplicationContext) applicationContext).refresh();
}
refresh 方法中的context 即 AnnotationConfigServletWebServerApplicationContext ，所以AnnotationConfigServletWebServerApplicationContext.refresh()即调用了父类的refresh
- refresh()
public final void refresh() throws BeansException, IllegalStateException {
try {
super.refresh();
}
catch (RuntimeException ex) {
stopAndReleaseWebServer();
throw ex;
}
}
我勒个去这是个啥（有点儿绕 =_=!! ~），别急，继续看super.refresh()
开始有点儿柳暗花明了 _~
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();
}
}
}
上下两张图有木有~ 有木有~ 如果之前不清楚如何启动的你是否已经开始“哦~”
-
获取 TomactServletWebServerFactory 、WebServer
createWebServer() 方法就是tomact启动的关键入口，这里边有两个比较关键的步骤
1). getWebServerFactory()
2). getSelfInitializer().onStartup(servletContext);
我们先看getWebServerFactory()，在看这个方法之前我们先看一下这个方法的返回值
ServletWebServerFactory ，看接口的实现你应该大概看到你想要东东了
但Springboot 是如何知道实例化TomactServletWebServerFacotry的呢，我们看一下getWebServerFactory里做了什么 springboot 之 tomact 启动 protected ServletWebServerFactory getWebServerFactory() { // 通过beanFactory 获取ServletWebServerFactory 类型的bean，经过跟代码我们知道，实际上返回的是 tomcatServletWebServerFactory String[] beanNames = getBeanFactory().getBeanNamesForType(ServletWebServerFactory.class); if (beanNames.length == 0) { throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to missing " + "ServletWebServerFactory bean."); } if (beanNames.length > 1) { throw new ApplicationContextException("Unable to start ServletWebServerApplicationContext due to multiple " + "ServletWebServerFactory beans : " + StringUtils.arrayToCommaDelimitedString(beanNames)); } return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class); } springboot 之 tomact 启动 那 TomcatServletWebServerFactory 是如何（何时）被加载的呢？
根据我们的猜测一般提供多种实现方式，但最终使用哪种实现一般会根据什么congfig或满足什么条件来决定，我们通过查找代码发现了（当然可能有其他捷径） ServletWebServerFactoryConfiguration
springboot 之 tomact 启动 不用多说一看就明白~
获取TomactServlerWebServerFactory后，我们看类的getWebServer方法都做了什么
public WebServer getWebServer(ServletContextInitializer... initializers) {
//终于。。。终于。。。。
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);
//上边对tomact进行的封装，再通过调用getTomcatWebServer返回tomact，我们看一下这个方法
return getTomcatWebServer(tomcat);
}
......
protected TomcatWebServer getTomcatWebServer(Tomcat tomcat) {
//貌似没什么东西，我们再看一下构造方法里做了什么
return new TomcatWebServer(tomcat, getPort() >= 0);
}
......
public TomcatWebServer(Tomcat tomcat, boolean autoStart) {
Assert.notNull(tomcat, "Tomcat Server must not be null");
this.tomcat = tomcat;
this.autoStart = autoStart;
//重点来了
initialize();
}
private void initialize() throws WebServerException {
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())) {
// Remove service connectors so that protocol binding doesn't
// happen when the service is started.
removeServiceConnectors();
}
});
//画星星的地方 ！！！！
// Start the server to trigger initialization listeners
this.tomcat.start();
// We can re-throw failure exception directly in the main thread
rethrowDeferredStartupExceptions();
try {
ContextBindings.bindClassLoader(context, context.getNamingToken(), getClass().getClassLoader());
}
catch (NamingException ex) {
// Naming is not enabled. Continue
}
// Unlike Jetty, all Tomcat threads are daemon threads. We create a
// blocking non-daemon to stop immediate shutdown
startDaemonAwaitThread();
}
catch (Exception ex) {
stopSilently();
destroySilently();
throw new WebServerException("Unable to start embedded Tomcat", ex);
}
}
}
至此我们已经将tomact的启动流程介绍完了，当然后续还有还有其他的流程：tomact 的启动配置、servlet / filter 加载还有一些启动过程中的事件广播等不在本文中展开长篇大论，本文旨在梳理流程 ”先脉络后细节“，也是为了将自己日常的梳理进行一个记录~