spring boot中servlet啟動原理
启动过程及原理
1 spring boot 应用启动运行run方法
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
FailureAnalyzers analyzers = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting(); try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
Banner printedBanner = printBanner(environment); //创建一个ApplicationContext容器
context = createApplicationContext();
analyzers = new FailureAnalyzers(context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner); //刷新IOC容器 refreshContext(context);
afterRefresh(context, applicationArguments);
listeners.finished(context, null);
stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
} return context;
} catch (Throwable ex) {
handleRunFailure(context, listeners, analyzers, ex); throw new IllegalStateException(ex);
}
2 createApplicationContext():创建IOC容器,如果是web应用则创建AnnotationConfigEmbeddedWebApplacation的IOC容器,如果不是,则创建AnnotationConfigApplication的IOC容器
public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context."
+ "annotation.AnnotationConfigApplicationContext"; /**
* The class name of application context that will be used by default for web
* environments. */
public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework."
+ "boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext";protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass; if (contextClass == null) { try {
//根据应用环境,创建不同的IOC容器
contextClass = Class.forName(this.webEnvironment ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS);
} catch (ClassNotFoundException ex) { throw new IllegalStateException( "Unable create a default ApplicationContext, "
+ "please specify an ApplicationContextClass",
ex);
}
} return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass);
}
3 refreshContext(context) spring boot刷新IOC容器(创建容器对象,并初始化容器,创建容器每一个组件)
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context); if (this.registerShutdownHook) { try {
context.registerShutdownHook();
} catch (AccessControlException ex) { // Not allowed in some environments. }
}
}
4 refresh(context);刷新刚才创建的IOC容器
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}5 调用父类的refresh()的方法
public void refresh() throws BeansException, IllegalStateException {
Object var1 = this.startupShutdownMonitor;
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(); this.onRefresh(); this.registerListeners(); this.finishBeanFactoryInitialization(beanFactory); this.finishRefresh();
} catch (BeansException var9) { if (this.logger.isWarnEnabled()) { this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
} this.destroyBeans(); this.cancelRefresh(var9); throw var9;
} finally { this.resetCommonCaches();
}
}
}
6 抽象父类AbstractApplicationContext类的子类EmbeddedWebApplicationContext的onRefresh方法
@Override protected void onRefresh() {
super.onRefresh(); try {
createEmbeddedServletContainer();
} catch (Throwable ex) { throw new ApplicationContextException("Unable to start embedded container",
ex);
}
}
7 在createEmbeddedServletContainer放啊发中会获取嵌入式Servlet容器工厂,由容器工厂创建Servlet
private void createEmbeddedServletContainer() {
EmbeddedServletContainer localContainer = this.embeddedServletContainer;
ServletContext localServletContext = getServletContext(); if (localContainer == null && localServletContext == null) {
//获取嵌入式Servlet容器工厂
EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
//根据容器工厂获取对应嵌入式Servlet容器 this.embeddedServletContainer = containerFactory
.getEmbeddedServletContainer(getSelfInitializer());
} else if (localServletContext != null) { try {
getSelfInitializer().onStartup(localServletContext);
} catch (ServletException ex) { throw new ApplicationContextException("Cannot initialize servlet context",
ex);
}
}
initPropertySources();
}
8 从IOC容器中获取Servlet容器工厂
//EmbeddedWebApplicationContext#getEmbeddedServletContainerFactory protected EmbeddedServletContainerFactory getEmbeddedServletContainerFactory() {
// Use bean names so that we don't consider the hierarchy
String[] beanNames = getBeanFactory()
.getBeanNamesForType(EmbeddedServletContainerFactory.class);
if (beanNames.length == 0) {
throw new ApplicationContextException(
"Unable to start EmbeddedWebApplicationContext due to missing "
+ "EmbeddedServletContainerFactory bean.");
}
if (beanNames.length > 1) {
throw new ApplicationContextException(
"Unable to start EmbeddedWebApplicationContext due to multiple "
+ "EmbeddedServletContainerFactory beans : "
+ StringUtils.arrayToCommaDelimitedString(beanNames));
}
return getBeanFactory().getBean(beanNames[0],
EmbeddedServletContainerFactory.class);
}
9 使用Servlet容器工厂获取嵌入式Servlet容器,具体使用哪一个容器工厂看配置环境依赖
this.embeddedServletContainer = containerFactory .getEmbeddedServletContainer(getSelfInitializer());
10 上述创建过程 首先启动IOC容器,接着启动嵌入式Servlet容器,接着将IOC容器中剩下没有创建的对象获取出来,比如自己创建的controller
// Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory);
protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) { // Initialize conversion service for this context.
if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
beanFactory.setConversionService(
beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
} // Register a default embedded value resolver if no bean post-processor // (such as a PropertyPlaceholderConfigurer bean) registered any before: // at this point, primarily for resolution in annotation attribute values.
if (!beanFactory.hasEmbeddedValueResolver()) {
beanFactory.addEmbeddedValueResolver(new StringValueResolver() {
@Override public String resolveStringValue(String strVal) { return getEnvironment().resolvePlaceholders(strVal);
}
});
} // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false); for (String weaverAwareName : weaverAwareNames) {
getBean(weaverAwareName);
} // Stop using the temporary ClassLoader for type matching.
beanFactory.setTempClassLoader(null); // Allow for caching all bean definition metadata, not expecting further changes. beanFactory.freezeConfiguration(); // Instantiate all remaining (non-lazy-init) singletons. beanFactory.preInstantiateSingletons();
}
看看 preInstantiateSingletons方法
public void preInstantiateSingletons() throws BeansException { if (this.logger.isDebugEnabled()) { this.logger.debug("Pre-instantiating singletons in " + this);
}
List<String> beanNames = new ArrayList(this.beanDefinitionNames);
Iterator var2 = beanNames.iterator(); while(true) { while(true) {
String beanName;
RootBeanDefinition bd; do { do { do { if (!var2.hasNext()) {
var2 = beanNames.iterator(); while(var2.hasNext()) {
beanName = (String)var2.next();
Object singletonInstance = this.getSingleton(beanName); if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton)singletonInstance; if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() { public Object run() {
smartSingleton.afterSingletonsInstantiated(); return null;
}
}, this.getAccessControlContext());
} else {
smartSingleton.afterSingletonsInstantiated();
}
}
} return;
}
beanName = (String)var2.next();
bd = this.getMergedLocalBeanDefinition(beanName);
} while(bd.isAbstract());
} while(!bd.isSingleton());
} while(bd.isLazyInit()); if (this.isFactoryBean(beanName)) {
final FactoryBean<?> factory = (FactoryBean)this.getBean("&" + beanName);
boolean isEagerInit; if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
isEagerInit = ((Boolean)AccessController.doPrivileged(new PrivilegedAction<Boolean>() { public Boolean run() { return ((SmartFactoryBean)factory).isEagerInit();
}
}, this.getAccessControlContext())).booleanValue();
} else {
isEagerInit = factory instanceof SmartFactoryBean && ((SmartFactoryBean)factory).isEagerInit();
} if (isEagerInit) { this.getBean(beanName);
}
} else {
//注册bean this.getBean(beanName);
}
}
}
}
是使用getBean方法来通过反射将所有未创建的实例创建出来
使用嵌入式Servlet容器:
优点: 简单,便携
缺点: 默认不支持jsp,优化定制比较复杂
使用外置Servlet容器的步骤:
1 必须创建war项目,需要剑豪web项目的目录结构
2 嵌入式Tomcat依赖scope指定provided
3 编写SpringBootServletInitializer类子类,并重写configure方法
public class ServletInitializer extends SpringBootServletInitializer {
@Override
protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
return application.sources(SpringBoot04WebJspApplication.class);
}
}
4 启动服务器
jar包和war包启动区别
jar包:执行SpringBootApplication的run方法,启动IOC容器,然后创建嵌入式Servlet容器
war包: 先是启动Servlet服务器,服务器启动Springboot应用(springBootServletInitizer),然后启动IOC容器
Servlet 3.0+规则
1 服务器启动(web应用启动),会创建当前web应用里面所有jar包里面的ServletContainerlnitializer实例
2 ServletContainerInitializer的实现放在jar包的META-INF/services文件夹下
3 还可以使用@HandlesTypes注解，在应用启动的时候加载指定的类。
外部Tomcat流程以及原理
① 启动Tomcat
② 根据上述描述的Servlet3.0+规则，可以在Spring的web模块里面找到有个文件名为javax.servlet.ServletContainerInitializer的文件，而文件的内容为org.springframework.web.SpringServletContainerInitializer，用于加载SpringServletContainerInitializer类
③看看SpringServletContainerInitializer定义
@HandlesTypes(WebApplicationInitializer.class)public class SpringServletContainerInitializer implements ServletContainerInitializer { /**
* Delegate the {@code ServletContext} to any {@link WebApplicationInitializer}
* implementations present on the application classpath.
* <p>Because this class declares @{@code HandlesTypes(WebApplicationInitializer.class)},
* Servlet 3.0+ containers will automatically scan the classpath for implementations
* of Spring's {@code WebApplicationInitializer} interface and provide the set of all
* such types to the {@code webAppInitializerClasses} parameter of this method.
* <p>If no {@code WebApplicationInitializer} implementations are found on the classpath,
* this method is effectively a no-op. An INFO-level log message will be issued notifying
* the user that the {@code ServletContainerInitializer} has indeed been invoked but that
* no {@code WebApplicationInitializer} implementations were found.
* <p>Assuming that one or more {@code WebApplicationInitializer} types are detected,
* they will be instantiated (and <em>sorted</em> if the @{@link
* org.springframework.core.annotation.Order @Order} annotation is present or
* the {@link org.springframework.core.Ordered Ordered} interface has been
* implemented). Then the {@link WebApplicationInitializer#onStartup(ServletContext)}
* method will be invoked on each instance, delegating the {@code ServletContext} such
* that each instance may register and configure servlets such as Spring's
* {@code DispatcherServlet}, listeners such as Spring's {@code ContextLoaderListener},
* or any other Servlet API componentry such as filters.
* @param webAppInitializerClasses all implementations of
* {@link WebApplicationInitializer} found on the application classpath
* @param servletContext the servlet context to be initialized
* @see WebApplicationInitializer#onStartup(ServletContext)
* @see AnnotationAwareOrderComparator */
@Override public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
throws ServletException {
List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>(); if (webAppInitializerClasses != null) { for (Class<?> waiClass : webAppInitializerClasses) { // Be defensive: Some servlet containers provide us with invalid classes, // no matter what @HandlesTypes says...
if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
WebApplicationInitializer.class.isAssignableFrom(waiClass)) { try {
//为所有的WebApplicationInitializer类型创建实例,并加入集合中
initializers.add((WebApplicationInitializer) 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");
AnnotationAwareOrderComparator.sort(initializers);
//调用每一个WebApplicationInitializer实例的onstartup方法 for (WebApplicationInitializer initializer : initializers) {
initializer.onStartup(servletContext);
}
}
}
在上面一段长长的注释中可以看到，SpringServletContainerInitializer将@HandlesTypes(WebApplicationInitializer.class)标注的所有WebApplicationInitializer这个类型的类都传入到onStartup方法的Set参数中，并通过反射为这些WebApplicationInitializer类型的类创建实例；
④ 方法最后,每一个WebApplicationInitilizer实现调用自己onstartup方法
⑤ 而WebApplicationInitializer有个抽象实现类SpringBootServletInitializer（记住我们继承了该抽象类），则会调用每一个WebApplicationInitializer实例（包括SpringBootServletInitializer）的onStartup方法：
public abstract class SpringBootServletInitializer implements WebApplicationInitializer {
//other code...
@Override
public void onStartup(ServletContext servletContext) throws ServletException {
// Logger initialization is deferred in case a ordered
// LogServletContextInitializer is being used
this.logger = LogFactory.getLog(getClass());
//创建IOC容器
WebApplicationContext rootAppContext = createRootApplicationContext(
servletContext);
if (rootAppContext != null) {
servletContext.addListener(new ContextLoaderListener(rootAppContext) {
@Override
public void contextInitialized(ServletContextEvent event) {
// no-op because the application context is already initialized }
});
}
else {
this.logger.debug("No ContextLoaderListener registered, as "
+ "createRootApplicationContext() did not "
+ "return an application context");
}
}
protected WebApplicationContext createRootApplicationContext(
ServletContext servletContext) {
//创建Spring应用构建器，并进行相关属性设置
SpringApplicationBuilder builder = createSpringApplicationBuilder();
StandardServletEnvironment environment = new StandardServletEnvironment();
environment.initPropertySources(servletContext, null);
builder.environment(environment);
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(AnnotationConfigEmbeddedWebApplicationContext.class);
//调用configure方法，创建war类型的web项目后，由于编写SpringBootServletInitializer的子类重写configure方法，所以此处调用的是我们定义的子类重写的configure方法
builder = configure(builder);
//通过构建器构建了一个Spring应用
SpringApplication application = builder.build();
if (application.getSources().isEmpty() && AnnotationUtils
.findAnnotation(getClass(), Configuration.class) != null) {
application.getSources().add(getClass());
}
Assert.state(!application.getSources().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.getSources().add(ErrorPageFilterConfiguration.class);
}
//启动Spring应用
return run(application);
}
//Spring应用启动，创建并返回IOC容器
protected WebApplicationContext run(SpringApplication application) {
return (WebApplicationContext) application.run();
}
}
SpringBootServletInitializer实例执行onStartup方法的时候会通过createRootApplicationContext方法来执行run方法，接下来的过程就同以jar包形式启动的应用的run过程一样了，在内部会创建IOC容器并返回，只是以war包形式的应用在创建IOC容器过程中，不再创建Servlet容器了。
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