spring boot 加载web容器tomcat流程源码分析
我本地的springboot版本是2.5.1，后面的分析都是基于这个版本
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.5.1</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
我们通过在pom文件中引入
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
来引入web容器，默认的web容器时tomcat。
本文章主要描述spring boot加载web容器 tomcat的部分，为了避免文章知识点过于分散，其他相关的如bean的加载，tomcat内部流程等不做深入讨论。
1、在springboot web工程中，全局上下文是AnnotationConfigServletWebApplicationContext
下面的部分，我们具体来看下
首先，我们的入口代码一般都是这样写的
public static void main(String[] args) {
SpringApplication.run(BootargsApplication.class,args);
}
跳转到run方法里面，依次会调用下面两个方法
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
return run(new Class<?>[] { primarySource }, args);
}
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}
首先会创建SpringApplication实例对象，跳转到SpringApplication的构造方法去看看，依次会调用如下方法
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
......
//本次不相关的代码全部省略掉，只保留相关代码
//这里的 this.webApplicationType=WebApplicationType.SERVLET， 我们来分析下这个代码的具体的执行赋值
this.webApplicationType = WebApplicationType.deduceFromClasspath();
......
}
继续跳转到WebApplicationType.deduceFromClasspath()去看看
//这个方法主要是在当前类路径下查找指定的class类是否存在，返回对饮枚举类型
static WebApplicationType deduceFromClasspath() {
// WEBMVC_INDICATOR_CLASS = "org.springframework.web.servlet.DispatcherServlet";
//我们通过pom文件引入spring-boot-starter-web，会简介引入spring-webmvc,上面这个类就在这个webmvc中，所以不会进入这个if分支
if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null) && !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
//SERVLET_INDICATOR_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" }
//javax.servlet.Servlet这个类存在于tomcat-embed-core中
//org.springframework.web.context.ConfigurableWebApplicationContext这个类存在于spring-web中
//这两个jar都是由spring-boot-starter-web间接引入的，所以也不会走这个分支
for (String className : SERVLET_INDICATOR_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
//所以会从这里返回
return WebApplicationType.SERVLET;
}
下面看下jar包的引入
回到new SpringApplication(primarySources).run(args)的调用来看run方法的代码
public ConfigurableApplicationContext run(String... args) {
.......
try {
......
//我们来看这个context的创建，context=new AnnotationConfigServletWebServerApplicationContext()下面来具体看这块的执行
context = createApplicationContext();
......
//后续几个部分会来说明这个方法
refreshContext(context);
......
}
catch (Throwable ex) {
......
}
try {
.......
}
catch (Throwable ex) {
.......
}
return context;
}
createApplicationContext()依次会调用如下方法
protected ConfigurableApplicationContext createApplicationContext() {
//这里的this.webApplicationType就是上面的WebApplicationType.SERVLET
return this.applicationContextFactory.create(this.webApplicationType);
}
//最终会调用到这个lambda表达式，入参就是上面的WebApplicationType.SERVLET
ApplicationContextFactory DEFAULT = (webApplicationType) -> {
try {
switch (webApplicationType) {
case SERVLET:
//会从这里返回
return new AnnotationConfigServletWebServerApplicationContext();
case REACTIVE:
return new AnnotationConfigReactiveWebServerApplicationContext();
default:
return new AnnotationConfigApplicationContext();
}
}
catch (Exception ex) {
throw new IllegalStateException("Unable create a default ApplicationContext instance, "
+ "you may need a custom ApplicationContextFactory", ex);
}
};
到这里，我们的上下文context就已经创建出来了，这块代码也比较简单。就不多说什么了
2、查找ServletWebServerFactory
再次回到new SpringApplication(primarySources).run(args)的调用来看run方法的代码
public ConfigurableApplicationContext run(String... args) {
.......
try {
......
//上面已经对context做过了讲解，context=new AnnotationConfigServletWebServerApplicationContext()
context = createApplicationContext();
......
//下面来看这个方法
refreshContext(context);
......
}
catch (Throwable ex) {
......
}
try {
.......
}
catch (Throwable ex) {
.......
}
return context;
}
点到refreshContext(context)
private void refreshContext(ConfigurableApplicationContext context) {
if (this.registerShutdownHook) {
shutdownHook.registerApplicationContext(context);
}
refresh(context);
}
继续点到refresh(context)
protected void refresh(ConfigurableApplicationContext applicationContext) {
//这里的applicationContext就是AnnotationConfigServletWebServerApplicationContext的对象，由于这个类没有refresh方法，会跳转到它的父类ServletWebServerApplicationContext的方法中去,我们继续点进去
applicationContext.refresh();
}
点到ServletWebServerApplicationContext的refresh方法
public final void refresh() throws BeansException, IllegalStateException {
try {
//继续跳转到父类AbstractApplicationContext方法
super.refresh();
}
catch (RuntimeException ex) {
WebServer webServer = this.webServer;
if (webServer != null) {
webServer.stop();
}
throw ex;
}
}
打开AbstractApplicationContext的refresh方法
//springboot 大部分的初始化工作是在这里完成的，不过这不是我们本地的重点，不相关的我们统统略过
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
......
try {
......
//继续点到这个方法，这里又会跳转到ServletWebServerApplicationContext这个类的方法
onRefresh();
.....
}
catch (BeansException ex) {
.....
}
finally {
.....
}
}
}
打开ServletWebServerApplicationContext的onRefresh方法
protected void onRefresh() {
super.onRefresh();
try {
//这里就是我们本次的重点，会在这里创建具体的web容器，我们点进去看看，还是ServletWebServerApplicationContext这个类的方法
createWebServer();
}
catch (Throwable ex) {
throw new ApplicationContextException("Unable to start web server", ex);
}
}
打开ServletWebServerApplicationContext的createWebServer方法
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
//第一次进来webServer servletContext都是null,会进到if分支里面
if (webServer == null && servletContext == null) {
//这里只是做个标记，不用关注，跳过
StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");
//这里就会来查找ServletWebServerFactory，也就是web容器的工厂,具体看下getWebServerFactory()方法，还是ServletWebServerApplicationContext这个类的方法
ServletWebServerFactory factory = getWebServerFactory();
createWebServer.tag("factory", factory.getClass().toString());
this.webServer = factory.getWebServer(getSelfInitializer());
createWebServer.end();
getBeanFactory().registerSingleton("webServerGracefulShutdown",
new WebServerGracefulShutdownLifecycle(this.webServer));
getBeanFactory().registerSingleton("webServerStartStop",
new WebServerStartStopLifecycle(this, this.webServer));
}
else if (servletContext != null) {
try {
getSelfInitializer().onStartup(servletContext);
}
catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context", ex);
}
}
initPropertySources();
}
打开ServletWebServerApplicationContext的getWebServerFactory方法
protected ServletWebServerFactory getWebServerFactory() {
// Use bean names so that we don't consider the hierarchy
//从beanFactory中查找ServletWebServerFactory类型的bean的定义，返回对应bean的名字
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));
}
//这里会从beanFactory中返回bean的名字为beanNames[0],类型为ServletWebServerFactory.class的bean对象，如果当前bean还未创建，则此时就会创建bean对象并返回
return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}
从上面的代码并看不出来实际的ServletWebServerFactory对象具体是什么？下面带着大家一起简单过下这部分的加载，这里具体就是springboot 加载bean的流程了，这部分的逻辑比较多，本次就不具体展开。关于springboot 加载bean的流程计划后续专门再写一篇。
springboot在启动过程中会在当前类路径下META-INF/spring.factories这个文件中，key=org.springframework.boot.autoconfigure.EnableAutoConfiguration的属性的作为bean的定义进行加载，在这过程中还会使用key=org.springframework.boot.autoconfigure.AutoConfigurationImportFilterfilter的属性作为过滤，配合META-INF/spring-autoconfigure-metadata.properties对这些类做一个过滤，剔除掉不符合的类(后续还会根据类上的注解判断是否要继续剔除)。
当前这些主要在spring-boot-autoconfigure-2.5.1.jar这个文件中
下面截取上面说的两部分,可以看到这里的过滤器就3个，具体不展开讨论了，自动导入的类就是下面的再加过滤去掉的
# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
......
#下面这个会在创建servelt中使用，下部分我们再关注它
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
#下面这个就是我们需要用到的
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
......
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
......
我们看下上面的org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration这个类，这个类在web 场景下，不会被剔除。会被加载。我们看看这个类，我们只看头部就可以了
这里我们看到类上有Import注解，会继续导入这几个类，
ServletWebServerFactoryConfiguration.EmbeddedTomcat.class,
ServletWebServerFactoryConfiguration.EmbeddedJetty.class,
ServletWebServerFactoryConfiguration.EmbeddedUndertow.class
这三个都是本次相关的，它们都是ServletWebServerFactoryConfiguration的内部类，我们进去看看，类的结构都是一样的，我们就看下ServletWebServerFactoryConfiguration.EmbeddedTomcat类吧
可以看到EmbeddedTomcat上面有ConditionalOnClass，ConditionalOnMissingBean这两个注解，
简单说下，ConditionalOnClass是表示当前类路径下存在对应类是加载
ConditionalOnMissingBean是表示当前beanFactory中没有对应类型bean定义的话加载
多个条件都是and的关系，有一个条件不成立，就不会去进行后续处理。
在这里EmbeddedTomcat类这两个条件是成立的，这时就会继续遍历当前类的所有方法，找到@Bean注解的方法，加载到beanFactory中去
而EmbeddedJetty，EmbeddedUndertow两个类条件是不成立的，就不会进行后续执行，剔除掉了
这里就会把EmbeddedTomcat.tomcatServletWebServerFactory这个方法进行加载，返回值是TomcatServletWebServerFactory类型，我们看下TomcatServletWebServerFactory类的继承图,可以看到它正好是继承了ServletWebServerFactory接口。
再次打开ServletWebServerApplicationContext的getWebServerFactory方法
protected ServletWebServerFactory getWebServerFactory() {
.......
//所以这里的逻辑实际上会执行ServletWebServerFactoryConfiguration.EmbeddedTomcat类的tomcatServletWebServerFactory方法，返回TomcatServletWebServerFactory对象,相关的属性注入等等这里就不讲述了
return getBeanFactory().getBean(beanNames[0], ServletWebServerFactory.class);
}
到这里，整个ServletWebServerFactory的查找就完成了
3、创建DispatcherServletRegistrationBean，DispatcherServlet
再看看上面的META-INF/spring.factories文件
# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
......
#现在我们重点来看这个类
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
......
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
......
我们打开org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration这个类看看
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
//我们当前只关注这ConditionalOnWebApplication、ConditionalOnClass注解
//ConditionalOnWebApplication是根据type来判断指定类是否存在
//当前的type是 Type.SERVLET，是来查找org.springframework.web.context.support.GenericWebApplicationContext类是否存在，这个类存在于spring-web中，所以这个条件是true
@ConditionalOnWebApplication(type = Type.SERVLET)
//这个注解上面说过了 ，就是查找指定的类是否存在，这个是查找DispatcherServlet.class是否存在，这里也会返回true
@ConditionalOnClass(DispatcherServlet.class)
//上面两个条件都成立，就会执行后续的操作，去遍历内部类和方法
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {
/**
* The bean name for a DispatcherServlet that will be mapped to the root URL "/".
*/
public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
/**
* The bean name for a ServletRegistrationBean for the DispatcherServlet "/".
*/
public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";
@Configuration(proxyBeanMethods = false)
//这里还是个条件，通过实现Condition接口，通过matches方法来判断
//DefaultDispatcherServletCondition这个类就在当前这个文件里，matches判断的结果也是true
@Conditional(DefaultDispatcherServletCondition.class)
//ServletRegistration.class这个类存在于tomcat-embed-core里面，这个结果也是true
@ConditionalOnClass(ServletRegistration.class)
//上面两个条件成立，就会执行后续的操作，去遍历内部类和方法
@EnableConfigurationProperties(WebMvcProperties.class)
protected static class DispatcherServletConfiguration {
//beanFactory会创建这个DispatcherServletbean的定义，bean的名字就是dispatcherServlet
@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet(WebMvcProperties webMvcProperties) {
DispatcherServlet dispatcherServlet = new DispatcherServlet();
dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
dispatcherServlet.setEnableLoggingRequestDetails(webMvcProperties.isLogRequestDetails());
return dispatcherServlet;
}
@Bean
@ConditionalOnBean(MultipartResolver.class)
@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
public MultipartResolver multipartResolver(MultipartResolver resolver) {
// Detect if the user has created a MultipartResolver but named it incorrectly
return resolver;
}
}
@Configuration(proxyBeanMethods = false)
//和上面的一样，不说了
@Conditional(DispatcherServletRegistrationCondition.class)
//和上面的一样，不说了
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
//这里会要在查找DispatcherServletConfiguration.class，并执行加载bean定义的流程，这就是上面的类了
@Import(DispatcherServletConfiguration.class)
protected static class DispatcherServletRegistrationConfiguration {
@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
//ConditionalOnBean查找是否存在指定bean的定义，这个方法要注入参数，需要这个类，当前这里就是上面的dispatcherServlet方法定义的，这里也是存在的
@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
//DispatcherServlet dispatcherServlet这个就是dispatcherServlet这个方法定义的bean，在创建DispatcherServletRegistrationBean这个bean的时候，就会去查找dispatcherServlet是否存在，如果不存在，先创建dispatcherServlet这个bean,再创建DispatcherServletRegistrationBean
public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
webMvcProperties.getServlet().getPath());
registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
multipartConfig.ifAvailable(registration::setMultipartConfig);
return registration;
}
}
......
}
上面就是创建DispatcherServlet，DispatcherServletRegistrationBean的过程了
4、创建tomcat，加载Servlet.class,filter.class，监听器
再次回到ServletWebServerApplicationContext的createWebServer方法
private void createWebServer() {
WebServer webServer = this.webServer;
ServletContext servletContext = getServletContext();
if (webServer == null && servletContext == null) {
StartupStep createWebServer = this.getApplicationStartup().start("spring.boot.webserver.create");
//上面我们已经看到了这里，factory是TomcatServletWebServerFactory类的一个实例对象
ServletWebServerFactory factory = getWebServerFactory();
//这里还是做个标记，不用关注
createWebServer.tag("factory", factory.getClass().toString());
//这里就是具体创建tomcat了，这里的入参getSelfInitializer()是个lambda表达式，这个后续很重要
this.webServer = factory.getWebServer(getSelfInitializer());
createWebServer.end();
getBeanFactory().registerSingleton("webServerGracefulShutdown",
new WebServerGracefulShutdownLifecycle(this.webServer));
getBeanFactory().registerSingleton("webServerStartStop",
new WebServerStartStopLifecycle(this, this.webServer));
}
else if (servletContext != null) {
try {
getSelfInitializer().onStartup(servletContext);
}
catch (ServletException ex) {
throw new ApplicationContextException("Cannot initialize servlet context", ex);
}
}
initPropertySources();
}
private org.springframework.boot.web.servlet.ServletContextInitializer getSelfInitializer() {
return this::selfInitialize;
}
//是创建webServer的参数
private void selfInitialize(ServletContext servletContext) throws ServletException {
prepareWebApplicationContext(servletContext);
registerApplicationScope(servletContext);
WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
factory.getWebServer(getSelfInitializer())会调用到TomcatServletWebServerFactory的getWebServer的方法
public WebServer getWebServer(ServletContextInitializer... initializers) {
.......
//上面的入参会在这里传下去
prepareContext(tomcat.getHost(), initializers);
return getTomcatWebServer(tomcat);
}
点进prepareContext(tomcat.getHost(), initializers)去看看
protected void prepareContext(Host host, ServletContextInitializer[] initializers) {
......
ServletContextInitializer[] initializersToUse = mergeInitializers(initializers);
host.addChild(context);
//继续传下去
configureContext(context, initializersToUse);
postProcessContext(context);
}
再点到configureContext(context, initializersToUse)这个调用去看看
protected void configureContext(Context context, ServletContextInitializer[] initializers) {
//会传递给TomcatStarter，作为构造参数，下面我们去这里看看
TomcatStarter starter = new TomcatStarter(initializers);
......
}
下面我们去看看TomcatStarter这个类是怎么使用这个initializers这个构造参数的。
这个类不长
class TomcatStarter implements ServletContainerInitializer {
......
TomcatStarter(ServletContextInitializer[] initializers) {
//入参会作为它的成员属性
this.initializers = initializers;
}
@Override
public void onStartup(Set<Class<?>> classes, ServletContext servletContext) throws ServletException {
try {
for (ServletContextInitializer initializer : this.initializers) {
//会在这里调用onStartup方法，这里的入参就是ApplicationContextFacade的对象，里面包装了ApplicationContext，里面再包装了TomcatEmbeddedContext，这要就和tomcat联系起来了，下面的截图就是servletContext的对象结构
initializer.onStartup(servletContext);
}
}
catch (Exception ex) {
......
}
上面的initializer.onStartup(servletContext)会调用到ServletWebServerApplicationContext的selfInitialize方法
private void selfInitialize(ServletContext servletContext) throws ServletException {
//这里是将ApplicationContextFacade设置到当前的servletContext上
prepareWebApplicationContext(servletContext);
//这里是在beanFactory中注册application的scope
registerApplicationScope(servletContext);
//这里还是注册上下文相关的bean
WebApplicationContextUtils.registerEnvironmentBeans(getBeanFactory(), servletContext);
//我们重点来看这里getServletContextInitializerBeans()是定义个一个ServletContextInitializerBeans对象，我们点进去看看
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
beans.onStartup(servletContext);
}
}
protected Collection<ServletContextInitializer> getServletContextInitializerBeans() {
//这里的getBeanFactory()就是全局的beanFactory
return new ServletContextInitializerBeans(getBeanFactory());
}
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class<? extends ServletContextInitializer>... initializerTypes) {
this.initializers = new LinkedMultiValueMap<>();
//由于我们没有传initializerTypes这个参数，所以this.initializerTypes里面就只有ServletContextInitializer.class这个类
this.initializerTypes = (initializerTypes.length != 0) ? Arrays.asList(initializerTypes)
: Collections.singletonList(ServletContextInitializer.class);
//这里主要是从beanFactory中查找this.initializerTypes类型，我们进去看看，就是下面这个方法了
addServletContextInitializerBeans(beanFactory);
addAdaptableBeans(beanFactory);
List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
.flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
.collect(Collectors.toList());
this.sortedList = Collections.unmodifiableList(sortedInitializers);
logMappings(this.initializers);
}
private void addServletContextInitializerBeans(ListableBeanFactory beanFactory) {
for (Class<? extends ServletContextInitializer> initializerType : this.initializerTypes) {
//默认情况下这里找到就只有上面第3部分的DispatcherServletRegistrationBean对应的bean
for (Entry<String, ? extends ServletContextInitializer> initializerBean : getOrderedBeansOfType(beanFactory,
initializerType)) {
//这里的key是bean的名字,value就是bean对象，在进去看看，就是下面这个方法
addServletContextInitializerBean(initializerBean.getKey(), initializerBean.getValue(), beanFactory);
}
}
}
private void addServletContextInitializerBean(String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory) {
//会走到这个分支
if (initializer instanceof ServletRegistrationBean) {
//这里返回的servlet也还是第3部分DispatcherServlet对应的bean
Servlet source = ((ServletRegistrationBean<?>) initializer).getServlet();
//再点进去
addServletContextInitializerBean(Servlet.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof FilterRegistrationBean) {
Filter source = ((FilterRegistrationBean<?>) initializer).getFilter();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof DelegatingFilterProxyRegistrationBean) {
String source = ((DelegatingFilterProxyRegistrationBean) initializer).getTargetBeanName();
addServletContextInitializerBean(Filter.class, beanName, initializer, beanFactory, source);
}
else if (initializer instanceof ServletListenerRegistrationBean) {
EventListener source = ((ServletListenerRegistrationBean<?>) initializer).getListener();
addServletContextInitializerBean(EventListener.class, beanName, initializer, beanFactory, source);
}
else {
addServletContextInitializerBean(ServletContextInitializer.class, beanName, initializer, beanFactory,
initializer);
}
}
private void addServletContextInitializerBean(Class<?> type, String beanName, ServletContextInitializer initializer,
ListableBeanFactory beanFactory, Object source) {
//这里的initializers是个map,按照类型，bean对象进行加载，这里的type是javax.servlet.Servlet.class,value是上面的DispatcherServletRegistrationBean
this.initializers.add(type, initializer);
if (source != null) {
// Mark the underlying source as seen in case it wraps an existing bean
//将DispatcherServlet对应的bean加到这里
this.seen.add(source);
}
if (logger.isTraceEnabled()) {
String resourceDescription = getResourceDescription(beanName, beanFactory);
int order = getOrder(initializer);
logger.trace("Added existing " + type.getSimpleName() + " initializer bean '" + beanName + "'; order="
+ order + ", resource=" + resourceDescription);
}
}
再回到ServletContextInitializerBeans的构造方法,接着看后面的
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class<? extends ServletContextInitializer>... initializerTypes) {
...... //这里的内容上面已经看过了，我们现在看下面这句，点进去
addAdaptableBeans(beanFactory);
List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
.flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
.collect(Collectors.toList());
this.sortedList = Collections.unmodifiableList(sortedInitializers);
logMappings(this.initializers);
}
protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
//这句不用关注
MultipartConfigElement multipartConfig = getMultipartConfig(beanFactory);
//这句不用关注
addAsRegistrationBean(beanFactory, Servlet.class, new ServletRegistrationBeanAdapter(multipartConfig));
//点到这里去看看
addAsRegistrationBean(beanFactory, Filter.class, new FilterRegistrationBeanAdapter());
for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,
new ServletListenerRegistrationBeanAdapter());
}
}
private <T, B extends T> void addAsRegistrationBean(ListableBeanFactory beanFactory, Class<T> type,
Class<B> beanType, RegistrationBeanAdapter<T> adapter) {
//这里的beanType是 Filter.class,下面这句就是从beanFactory中获取所有类型为Filter.class的bean
List<Map.Entry<String, B>> entries = getOrderedBeansOfType(beanFactory, beanType, this.seen);
for (Entry<String, B> entry : entries) {
String beanName = entry.getKey();
B bean = entry.getValue();
//将bean放置到this.seen里面
if (this.seen.add(bean)) {
// One that we haven't already seen
//包装成RegistrationBean对象
RegistrationBean registration = adapter.createRegistrationBean(beanName, bean, entries.size());
int order = getOrder(bean);
registration.setOrder(order);
//同样放置到this.initializers里面
this.initializers.add(type, registration);
if (logger.isTraceEnabled()) {
logger.trace("Created " + type.getSimpleName() + " initializer for bean '" + beanName + "'; order="
+ order + ", resource=" + getResourceDescription(beanName, beanFactory));
}
}
}
}
再回到上面的addAdaptableBeans方法，看后面的
protected void addAdaptableBeans(ListableBeanFactory beanFactory) {
......//这里刚才说过了
//下面这部分不说了，这里基本和上面一样，不过处理的类型变成了ServletContextAttributeListener.class、ServletRequestListener.class、ServletRequestAttributeListener.class、HttpSessionAttributeListener.class、HttpSessionIdListener.class、HttpSessionListener.class、ServletContextListener.class这些类型
for (Class<?> listenerType : ServletListenerRegistrationBean.getSupportedTypes()) {
addAsRegistrationBean(beanFactory, EventListener.class, (Class<EventListener>) listenerType,
new ServletListenerRegistrationBeanAdapter());
}
}
再回到ServletContextInitializerBeans的构造方法,接着看后面的
public ServletContextInitializerBeans(ListableBeanFactory beanFactory,
Class<? extends ServletContextInitializer>... initializerTypes) {
......//这里刚才都说过了，看下面
//这里就是把上面所有获取到的相关的bean放置到this.sortedList中，下面我是我本地this.sortedList的截图
List<ServletContextInitializer> sortedInitializers = this.initializers.values().stream()
.flatMap((value) -> value.stream().sorted(AnnotationAwareOrderComparator.INSTANCE))
.collect(Collectors.toList());
this.sortedList = Collections.unmodifiableList(sortedInitializers);
logMappings(this.initializers);
}
这里ServletContextInitializerBeans的构造方法就完成了，再回过头去看看这个类的定义
public class ServletContextInitializerBeans extends AbstractCollection<ServletContextInitializer>
这个类继承了AbstractCollection类，那它就需要实现下面这个抽象方法
public abstract Iterator<E> iterator();
我们看看ServletContextInitializerBeans的iterator的方法
@Override
public Iterator<ServletContextInitializer> iterator() {
return this.sortedList.iterator();
}
看到了吧，这就是返回上面的this.sortedList.iterator()
我们再次回到ServletWebServerApplicationContext的selfInitialize方法
private void selfInitialize(ServletContext servletContext) throws ServletException {
......//这里上面都说过了
//getServletContextInitializerBeans()这个方法就是构造了ServletContextInitializerBeans
//这里的for循环也是调用了ServletContextInitializerBeans的iterator的方法，实际上遍历的也就是上面的this.sortedList
for (ServletContextInitializer beans : getServletContextInitializerBeans()) {
//这里就是把在beanFactory中查找到的Servlet.class,filter.class，监听器等等添加到tomcat容器中,我们就只进到servlet里面去看看
//进到DispatcherServletRegistrationBean里面去看看
beans.onStartup(servletContext);
}
}
//这个方法在DispatcherServletRegistrationBean的父类RegistrationBean中
//所有的Servlet.class,filter.class，监听器都会走到这里
public final void onStartup(ServletContext servletContext) throws ServletException {
//这里是返回的表述，不关注
String description = getDescription();
if (!isEnabled()) {
logger.info(StringUtils.capitalize(description) + " was not registered (disabled)");
return;
}
//这里由不同的子类去实现，DispatcherServletRegistrationBean会调用到ServletRegistrationBean中
register(description, servletContext);
}
//这个方法是在ServletRegistrationBean这个类中
@Override
protected ServletRegistration.Dynamic addRegistration(String description, ServletContext servletContext) {
String name = getServletName();
//这里的servletContext上面的ApplicationContextFacade的对象，这里就会将DispatcherServlet的bean对象加载到TomcatEmbeddedContext中，后续所有的http请求最后都会流转到DispatcherServlet去进行具体的分发
return servletContext.addServlet(name, this.servlet);
}
到这里Servlet.class,filter.class，监听器就全部加载到tomcat中去
5、创建RequestMappingHandlerMapping
再看看上面的META-INF/spring.factories文件
# Auto Configuration Import Filters
org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
org.springframework.boot.autoconfigure.condition.OnClassCondition,\
org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
......
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
......
#现在我们重点来看这个类
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
......
具体的加载和上面部分都类似，就不展开了，直接看我们需要的
//这里会创建RequestMappingHandlerMapping的bean
@Bean
@Primary
@Override
public RequestMappingHandlerMapping requestMappingHandlerMapping(
@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
@Qualifier("mvcConversionService") FormattingConversionService conversionService,
@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {
// Must be @Primary for MvcUriComponentsBuilder to work
return super.requestMappingHandlerMapping(contentNegotiationManager, conversionService,
resourceUrlProvider);
看下这个类的继承图
RequestMappingHandlerMapping实现了InitializingBean接口，会在bean对象创建后的invokeInitMethods方法中调用afterPropertiesSet方法,最终会调用的AbstractHandlerMethodMapping的afterPropertiesSet方法中
@Override
public void afterPropertiesSet() {
initHandlerMethods();
}
/**
* Scan beans in the ApplicationContext, detect and register handler methods.
* @see #getCandidateBeanNames()
* @see #processCandidateBean
* @see #handlerMethodsInitialized
*/
protected void initHandlerMethods() {
//这里查找beanFactory中的所有bean进行遍历
for (String beanName : getCandidateBeanNames()) {
if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
//点到这里去看看
processCandidateBean(beanName);
}
}
handlerMethodsInitialized(getHandlerMethods());
}
protected void processCandidateBean(String beanName) {
Class<?> beanType = null;
try {
//根据beanName获取对应bean的Class对象
beanType = obtainApplicationContext().getType(beanName);
}
catch (Throwable ex) {
// An unresolvable bean type, probably from a lazy bean - let's ignore it.
if (logger.isTraceEnabled()) {
logger.trace("Could not resolve type for bean '" + beanName + "'", ex);
}
}
//判断类上是否有Controller.class，RequestMapping.class注解
if (beanType != null && isHandler(beanType)) {
//这里就会解析beanName上的所有方法进行遍历，查找有 RequestMapping.class注解的方法，创建RequestMappingInfo对象，放置到registry属性中(在AbstractHandlerMethodMapping)中，这样我们所有定义的controller中的http请求就会全部被扫描到
detectHandlerMethods(beanName);
}
}
6、加载RequestMappingHandlerMapping到DispatcherServlet中
在我们第一次请求的时候，会执行到DispatcherServlet的initStrategies方法，这个方法只会执行一次
protected void initStrategies(ApplicationContext context) {
......
这就会加载之前查找到的RequestMappingHandlerMapping中的我们定义的controller
initHandlerMappings(context);
......
}
会调用到这里
private void initHandlerMappings(ApplicationContext context) {
this.handlerMappings = null;
if (this.detectAllHandlerMappings) {
// Find all HandlerMappings in the ApplicationContext, including ancestor contexts.
//这里会在beanFactory中查找所有HandlerMapping.class的bean,其中就包含我们第5部分的RequestMappingHandlerMapping
Map<String, HandlerMapping> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(context, HandlerMapping.class, true, false);
if (!matchingBeans.isEmpty()) {
//将所有查找到的放置到handlerMappings中
this.handlerMappings = new ArrayList<>(matchingBeans.values());
// We keep HandlerMappings in sorted order.
AnnotationAwareOrderComparator.sort(this.handlerMappings);
}
}
......
}
当我们浏览器请求的时候，最终会走到DispatcherServlet的doDispatch的方法，处理我们的请求并返回,简单看看
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
......
try {
ModelAndView mv = null;
Exception dispatchException = null;
try {
processedRequest = checkMultipart(request);
multipartRequestParsed = (processedRequest != request);
// Determine handler for the current request.
//在这里，就会请求request的请求路径去查找实际要执行的controller的方法，点进去看看
mappedHandler = getHandler(processedRequest);
......
}
@Nullable
protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
if (this.handlerMappings != null) {
//这其实就是根据遍历，查找对应的路径，这个this.handlerMappings就是就是在initHandlerMappings方法中赋值的
for (HandlerMapping mapping : this.handlerMappings) {
HandlerExecutionChain handler = mapping.getHandler(request);
if (handler != null) {
return handler;
}
}
}
return null;
}
到这里，springboot 加载web容器的整个流程基本就算完成了，这块涉及的东西比较多，所以说的可能比较粗，大家见谅。